1999 AAPG Eastern Section Meeting Abstracts

Use of Polyelectrolyte-micelle Coacervates for In-situ Trapping of Organic Plumes

BANZIGER, J., Dept. of Geology, P. DUBIN, Dept. of Chemistry and Center for Earth and Environmental Science, and G. FILIPPELLI, Dept. of Geology and Center for Earth and Environmental Science, IUPUI, Indianapolis, IN

            A promising new methodology for treating sub-surface contaminant plumes involves the coacervation of polyelectrolyte-micelles. Polyelectrolytic surfactants can form micelles, bipolar organic molecules, which can adsorb onto solid surfaces through coacervation. In this state, they act as filters, with the ability to bind organic molecules. Furthermore, their charge characteristics can be altered after organic trapping, allowing for a re-solubilization of the organic molecules. In this way, this chemical technology could be used to emplace a reversible geochemical fence downstream of polluting organic plumes.

            We performed the first test of this technology with geologic materials to assess the potential of the theoretical possibilities mentioned above. Using sand and a model organic solvent with well-known chemical characteristics (Orange OT dye in an ethanol matrix), we attempted to first coat sand with polyelectrolyte-micelle coacervate, then to adsorb the model organic onto the sand. Our tests were successful. Little of the model organic adsorbed on to the plain sand, and little adsorbed when the coarcervate had previously been formed. Maximum adsorption occurred when the polyelectrolyte micelles were titrated to the point of coacervation in the presence of sand, followed by treatment with the model organic solution. This indicates that a polyectrolyte-micelle solution could be introduced into a subsurface system, then driven to coacervation via ionic strength changes. Questions to address through experiments and field work include testing this technique on a range of organic pollutants, examining permeability loss with increased organic trapping, and assessing the feasibility of adjusting ionic strengths and pH in the subsurface.

Where are all those darn reefs? An appraisal of the potential for more Silurian reef discoveries in the Illinois basin.

CLUFF, ROBERT M. and CATHERINE M. MURPHY, The Discovery Group, Inc., 1560 Broadway, Ste 1470, Denver, CO 80202-5150 bobcluff@discovery-group.com

            Intensive subsurface and seismic exploration in southern Illinois has resulted in at least 26 known reef discoveries over a 90 year period. Many other small oil fields in Illinois are possibly reef-related, but have not been proven by drilling or seismic to be underlain by Silurian reefs. The last significant reef discoveries were made in 1973-74 after an intensive 2-D CDP seismic effort by several major oil companies. These data have subsequently been re-sold and re-interpreted numerous times, but no additional large reefs have been found.

            The average recovery from Silurian reef fields is ~5800 bbls/ac or 116 MBO per 20-ac location, which is substantially above the typical well recovery in this state. The compelling economics of reef production draws many new players to the reef play. With a steady stream of new explorers and new ideas, it begs the question: “Where are all those darn reefs, and why aren’t we finding new reefs all the time?”

            Consideration of the 2-D seismic density over the reef trend suggests most if not all reefs over 160 acres in size have been discovered, and the remaining target size is < 80 acres. This is based on: 1) average shooting density on 2 x 2 mile CDP grid; 2) reefs are roughly circular in shape; 3) reefs are randomly distributed with respect to the seismic grid; 4) 1970 vintage 2-D data would detect a reef if it crossed the reef. From simple geometric analysis, this exploration effort should have found 100% of the reefs >640 ac in size, 80% of the 320 ac reefs, 60% of the 160 ac reefs, and 40% of the 80 ac reefs. In fact the 1970’s efforts found three fields: Nashville (~620 ac), Brubaker (70 ac) and Lillyville North (50 ac). Reefs become increasing difficult to identify on noisy seismic data as they get smaller, so the probability of detection goes down and assumption #4 is violated. In our opinion the industry is and has always been finding reefs, but they are mostly very small fields. The exploratory effort associated with defining such tiny reef targets is an economic problem.

Sequential Disconformities in the Devonian Succession of Southern Indiana and Northwestern Kentucky

CONKIN, JAMES E., Dept. of Geography & Geosciences, Univ. of Louisville, Louisville, KY; BARBARA CONKIN, Louisville, KY; and M. R. DASARI, Air Pollution Board, Cincinnati, OH

            In southern Indiana and northwestern Kentucky, 18 paracontinuous disconformities separate 17 sedimentary packages within the Middle-Upper Devonian, while paracontinuity 19 marks the Upper Devonian-Lower Mississippian boundary and paracontinuity 20 marks the Kinderhookian-Osagean boundary. At the base of the Devonian sequence, the contact is a paraconformable disconformity between the Middle Silurian Louisville Limestone and the Early? (Emsian)-Middle (Eifelian) Devonian Jeffersonville Limestone, with an estimated time gap of 25-30 million years along the unconformity.

            Nineteen fish bone beds are associated with and immediately overlie paracontinuities 2-20, while the first paracontinuity (between the underlying Amphipora ramosa Zone and the overlying Brevispirifer gregarius Zone of the Jeffersonville Limestone) is not associated with a bonebed.

            The 17 sedimentary packages are of various stratigraphic taxa, as members, formations, groups, and series and are discriminated not only by the widespread disconformities at their bases, but also by fossil zones. Further, these sedimentary packages are enclosed in a framework bracketed by distinct and separately recognizable metabentonites: the Kawkawlin, Onondaga Indian Nation, and Tioga in the Middle Devonian, and the Belpre, Center Hill, and Howardstown in the Upper Devonian. There are at least 33 less important metabentonites, but some of marker significance, as the Lake Chelan Metabentonite, associated with bone bed 4 at the base of the Upper Paraspirifer acuminatus -Spirifer duodenarius Zone of the Jeffersonville.

Interpretation of Precambrian Geology along the Structurally Restored Ohio Consortium for Continental Reflection Profiling (COCORP) Seismic Lines

DEAN, STUART L., University of Toledo, OH; MARK T. BARANOSKI, Ohio Division of Geological Survey, Columbus, OH; and JOHN L. WICKS, Red Bird Producing, Wooster, OH

            A structural restoration of reprocessed Ohio COCORP seismic lines has clarified the configuration and chronological development of the Fort Wayne rift (an arm of the East Continent Rift Basin) and a series of sediment-filled Precambrian foreland basins east of the previously accepted Grenville Front. Total shortening at the top of the Grenville sequence is about 13% across Ohio from the West Virginia border to the western boundary of the Grenville tectonic zone in west-central Ohio. Shortening appears to culminate within the tectonic zone at about 16.5%.

    Grenville foreland basins are defined by (1) marked impedance contrasts between essentially horizontal basin fill and underlying Grenville metamorphic rocks, and (2) abnormally low interval velocities in basin strata. Structural restoration of fault displacements at the basin fill/Grenville metamorphic rock unconformity reveals a geometry suggestive of three large foreland basins that were later progressively partitioned as Grenville thrusting advanced from east to west.

    Thrusting occurred west of the Grenville Province and well into Indiana, involving fill strata of the East Continent Rift Basin, as well as underlying rocks of the Central Granite-Rhyolite Province. However, shortening decreases significantly westward; and fill strata show a maximum of 10% shortening at the eastern border of the East Continent Rift Basin and approximately 2% at the western end.

Evaluating Long-term Stratigraphic Organization of Peritidal Carbonate Sequences

DRUMMOND, CARL N., and ALEX O. JAMES, Dept. of Geosciences, Indiana Univ. Purdue Univ. Fort Wayne

            The long-term organization exhibited by peritidal sections occurs on a scale of 10’s to 100’s of meters; yet, the question persists, what specific stratigraphic characteristics are responsible for these changes? Two end-member hypotheses present themselves. First, thickness variation within peritidal sections could occur across all facies types, wherein regions of a stratigraphic section are generally thicker or thinner bedded than the long-term average. Such cross-lithologic thickness variation could be driven by gradual changes in long-term rates of accommodation space creation. Alternatively, a second hypothesis suggests that there exist thickness-frequency relationships unique to specific lithologies. Vertical variation in the abundance of these different facies would then result in variation about the average bed thickness. Long-term variation in bed-thickness as driven by lithology-specific thickness relationships could be the result of shifting facies mosaics across the depositional surface, or to more strictly allogenic changes in facies abundance in an up-dip or down-dip direction driven by eustasy or tectonism. Preliminary analysis of the Ordovician Kindblade and West Spring Creek Formations of southern Oklahoma supports the hypothesis of lithology-specific thickness variation. Algal boundstone facies average 0.78 m while mud and grain-rich particulate carbonate beds while more abundant, average only 0.25 m in thickness. Stratigraphic distribution of boundstone within the sequence strongly correlates with the shape of the Fischer plot constructed for this sequence. Elementary forward models of carbonate deposition tend to support the notion of lithology-specific thickness variation as being the dominant factor in controlling large-scale stratal architecture within peritidal sequences.

Evidence of Intrinsic Remediation at a Crude Oil Release Site

GATES, MICHAEL M., ARCADIS Geraghty & Miller, Inc., 5100 East Skelly Drive, Ste. 1000, Tulsa, OK 74135; TOM CROSSMAN, Tampa, FL; and DAVID S. LILES, Raleigh, NC

            The presence and fate of residual crude oil in soil and groundwater at a release site was investigated to determine the significance of natural attenuation processes. A biotreatability analysis of the soils and a biochemical analysis of the groundwater was completed to demonstrate and quantify intrinsic remediation of the residual hydrocarbons. The site soils were found to contain metabolically active microorganisms whose metabolic needs for oxygen characterizes them as either aerobic or facultatively anaerobic. Biochemical analysis of site groundwater provides evidence of active intrinsic remediation and the stabilization of the plume over a relatively short distance from the release area. Site data suggest that biodegradation of residual crude oil is occurring through both aerobic and anaerobic processes with aerobic respiration, sulfanogenesis, and methanogenesis all being important degradation mechanisms. Sulfanogenesis was found to be largely responsible for the total assimilative capacity of the aquifer to degrade hydrocarbons. The results of this study demonstrate that intrinsic bioremedation can provide a remediation alternative that is as efficient as actively engineered processes such as pump and treat.

Manufactured Gas Plant: Process, Practice and Environmental Consequences

GHOSH, SWAPAN S., Indiana Gas Company, Indianapolis, IN

            Gas manufacturing by coal carbonization and carbureted water gas process was a significant industry in Indiana between ca 1850 and 1940. Polishing and purification of the initial product yielded several byproducts such as coke, tar and ammonia, and waste such as purifier waste, clinker and waste water. Unused tar and other process wastes were left on-site in holders, containers or as fill materials. Chemical components of the byproducts and wastes, which are of environmental concern, consist of BTEX, PAHs, phenolics, inorganic nitrogen compounds and some metals. However, assessment of groundwater and soil contamination in several MGP sites indicates that benzene and a few carcinogen PAHs essentially control the environmental risk associated with the MGP sites.

            Investigation and prediction of fate and transport of the MGP waste varies from being elemental: as in identifying purifier waste (cobalt blue, pumice-like materials and naphthalene odor) to elaborate as in the analysis of impact of tar in the environment (three phases - LNAPL, DNAPL and dissolved constituents). Experience from several MGP sites indicates that a site specific investigation should be conducted to assess the risks to the environment for selection of appropriate technology/remedy for cleanup

Mining Geology of Western Kentucky Coals

GREB, STEPHEN F., and DAVID A. WILLIAMS, Kentucky Geological Survey, University of Kentucky, Lexington, KY

            Regional analysis of mined coal beds, mine visits, and discussions with mine inspectors and engineers are used to summarize critical mining geology factors in western Kentucky underground coal mines. Although mines are susceptible to roof falls caused by facies changes in mine roofs, the lateral continuity of coal seams and surrounding strata in western Kentucky causes most of these facies-change obstacles to be very localized, especially when compared to those in the Eastern Kentucky Coal Field. The widespread continuity leads to specific geologic conditions for each seam, rather than similar conditions for all seams, a factor that should be recognized in geologic modeling.

             The most common roof problems in Springfield (W. Ky. No. 9) coal mines are "slips" or slickensided fractures, which appear to be more developed in the hard, black shale above this coal than in shales above other coals. Locally, Springfield coal mines also encounter floor heaving related to thick, relatively moist underclays. Similar heaving is noted in the Herrin coal, but Herrin mine roofs have problems related to a weak, calcareous claystone, which degrades rapidly on exposure, rather than roof slips. The Baker coal (W. Ky. No. 13) also has a claystone roof, but it is a seat earth, and roof problems in it are related to the height of rider coals, which are not common above other mined coals. In contrast to these three coals, mines in the W. Ky. No. 4 coal more commonly encounter geologic obstacles related to narrow paleochannels, stackrock, and undulating floor elevations associated with syndepositional faulting, not commonly observed in the other coals. Superimposed on all of these features, in each of the coals, are regional faulting, north–south oriented regional stress fractures, and fractures below areas of low cover. Fractures and faulting may also act as conduits for water and sulfate-bearing fluids, both locally affect the mining geology of western Kentucky coals.

Pound Gap-The first Distinguished Geologic Site in Kentucky

GREB, STEPHEN F., DONALD R. CHESNUT, JR., GARLAND R. DEVER, JR., DAVID HARRIS, FRANK R. ETTENSOHN, JR., CHARLES MASON, WILLIAM M. ANDREWS, PAUL HOWELL, CORTLAND F. EBLE, MICHAEL R. CAUDILL, KAREN HOUCK, and W. JOHN NELSON, Kentucky Society of Professional Geologists, Lexington, KY

            New roadcuts on U.S. Highway 23 through Pound Gap on Pine Mountain in eastern Kentucky have exposed a nearly complete, 600-m-thick (2000-ft-thick) section of Upper Devonian through Lower Pennsylvanian strata. The section occurs on the leading edge of the Pine Mountain thrust fault, and strata are exposed in mostly undeformed, moderately dipping beds. Several sequences and associated boundaries are exposed in the outcrops, which is important because equivalent beds occur at depths of more than 600 m (2,000 ft) in front of the thrust. Because of its significance, the Pound Gap roadcut was designated as the first official Distinguished Geologic Site in Kentucky by the Kentucky Society of Professional Geologists.

            The base of the section occurs in the Huron Member of the Ohio Shale, and more than 81 m (270 ft) of the Upper Devonian is exposed. Mississippian strata consist of 33 m (110 ft) of the Sunbury Shale, overlain by 90 m (300 ft) of turbidite-dominated siliciclastics of the Grainger Formation, overlain by 167 m (556 ft) of shallow-water ramp carbonates and shales of the Newman Limestone and 279 m (930 ft) of mixed carbonates, tidally influenced clastics, red and green paleosols, and other clastics of the Pennington Formation. The Pennington is disconformably overlain by more than 30 m (100 ft) of Lower Pennsylvanian, fluvial, crossbedded, quartz-pebble conglomerates assigned to the undifferentiated Warren Point-Sewannee sandstones.

POGO — What It Is and What You Can Do with It

GRUBAUGH, WILLIAM A., MICHELLE L. BARUTH, CGAS Exploration, Inc., JOSEPH G. WELLS and LAWRENCE H. WICKSTROM, Ohio Division of Geological Survey, Columbus, OH

            The Production of Oil and Gas in Ohio (POGO) database contains production data gathered directly from petroleum companies and individuals plus all production data submitted to the state since 1983. Overall, the database contains more than 500,000 yearly records for more than 58,000 unique wells. The yearly records include some data as old as 1921 and extend through 1997. The database also contains over 84,000 monthly production records.

            Using this statewide production data, one can quickly create production histories, decline curves, and calculations such as estimated ultimate recoveries (EUR) for wells around the state from many different producing formations. Simple EUR’s have been calculated for all applicable records and imported to an exploration-mapping environment, posted to a statewide base map, and contoured.

            The statewide EUR contour map provides a powerful tool for the explorationist. Analysis of areas of high, low, and intermediate ultimate recovery values may challenge some long-held beliefs of “good” or “bad” areas. This analysis method also offers the ability to analyze potential depletion in established production trends by comparing wells drilled before 1980 versus wells drilled in the 1980’s and 1990’s.

            Overlaying the EUR contours on structure contour maps (top of “Big Lime”, Top of “Packer Shell”, and Knox unconformity surface) statewide illustrates large-scale structural controls on production.

            As development, editing, and updating of POGO continues, more accurate and reliable studies will be possible using individual producing formations. This information should prove useful in the decision-making process of evaluating uneconomic wells (for uphole or downhole potential) before they are plugged.

Compartmentalized Sandstone Ridges in the Cypress Formation (Mississippian) of the Illinois Basin

GRUBE, JOHN P., grube@isgs.uiuc.edu, and BEVERLY SEYLER, Illinois State Geological Survey, 615 East Peabody Drive, Champaign, IL 61820

            The Mississippian Cypress Formation is the most prolific producing horizon in the Illinois Basin. Nearly one billion barrels of oil have been produced from the shallow sandstone reservoirs in the Cypress.

            Vertically stacked, lenticular, ridge forming sandstones are a common sandbody configuration in the middle and upper part of the Cypress Formation The sandstones that make up the primary reservoirs vary from 1 to 2 miles in length, up to a 1/2 of a mile in width and may be greater than 40 feet in thickness. Sandstones of this thickness are an accumulation of vertically stacked lenses that are commonly less than 10 feet thick. The ridges are typically arranged in a group with a subparallel alignment and trend in a northeast-southwest to north-south orientation. Examples of these ridges can be found at Lawrence, Parkersburg, Richview and Tamaroa fields in Illinois. At Lawrence Field, the middle Cypress sandstone is made up of a stacked complex of ridges that are embedded in thin, elongate sheet sandstones that are aligned with the ridges. Ridge sandstones at Richview and Tamaroa fields occur in the upper Cypress and change facies laterally to shale with no sheet extensions.

            Discrete reservoir compartments are created within the fields by shale beds or shaly sandstones that separate the vertically stacked sandstone lenses. Spontaneous potential and gamma-ray log character, as well as core data, show that shales, ranging in thickness from 10 feet to less than 1 foot, separate the sandstones in the upper Cypress. Middle Cypress sandstone lenses may be separated by shaly, more impermeable sandstone beds. Lenses may also coalesce locally forming a single compartment. Combined stratigraphic/structural trapping occurs where stacked, compartmentalized sandstone lenses lap onto and drape over a structure. Stratigraphy and geometry indicate that these sandstones were deposited in tidally influenced, shallow marine environments.

            Optimal petroleum recovery requires a knowledge of the architecture of these reservoir compartments. Banked and bypassed oil may remain in these compartments due to the drill pattern of production and injection wells. Also, waterflood success requires that production and injection wells penetrate laterally continuous compartments. Correlation of individual compartments is therefore critical.

Shallow Geophysics for Investigation of a Creosote Contaminated Site in Central Ohio

GUY, ERICH D., DANIELS, JEFFREY J., and RADZEVICIUS, STANLEY J., Department of Geological Sciences, The Ohio State University, Columbus, OH

            Electromagnetic (EM) and Ground penetrating radar (GPR) surveys were conducted at an industrial site that formerly operated as a creosote wood treating facility in order to accomplish two objectives: 1) to delineate the extent of creosote contamination at the site, and 2) to locate buried pipes, tanks or other subsurface features that could lead to further contamination if ruptured during remediation. Data interpretations were confirmed by exploratory trenching and soil sampling subsequent to the completion of this study. EM data were useful for mapping the extent of creosote within surficial soils. The GPR data proved successful in locating back-filled trenches and pipes at the site, as well as vaults and a pit filled with pure creosote product. Both parallel dipole (co-pole) and crossed dipole (cross-pole) data were collected during the GPR survey. Cross-pole data were more useful for site characterization at this location, as images produced using co-pole data had a poor signal to noise ratio due to site conditions.

Non-glacial Origin on Glacial-like Deposits

HALL, ROBERT D., Dept. of Geology, IUPUI, Indianapolis, IN

            New radiocarbon ages from diamictons and associated sediments in Indiana and Ohio average about 40,000 RCYBP. These deposits may reflect climatic warming that lasted only a few millennia but triggered melting of permafrost that induced extensive viscous flows. These diamictons were originally assumed to be glacial (i.e. till) and commonly assigned to a middle Wisconsinan glaciation, in some cases on the basis of radiocarbon dating. However, as advocacy of middle Wisconsinan glaciation became climatically problematic, the diamictons were commonly reassigned to either the Illinoian or the late Wisconsinan glaciations. However, reassignment requires rejection of middle Wisconsinan radiocarbon ages. A nonglacial viscous-flow origin fits better with growing global evidence for middle Wisconsinan climatic warming.

Advanced Characterization of Fractured Reservoirs in Carbonate Rocks: The Michigan Basin

HARRISON, WILLIAM B.,III, Dept. Geosciences, Western Michigan University, Kalamazoo, MI and JAMES R. WOOD, Michigan Tech. Univ., Houghton, MI

            An industry-university consortium has been formed to develop a comprehensive model for fractured carbonate reservoirs in the Michigan basin. This three-year project, co-sponsored by the U.S. Department of Energy, will combine traditional historical data and modern logging tools in a novel way to produce a new methodology for characterizing fractured reservoirs in carbonate rocks. Advanced visualization software will be used to fuse the data and to image it on a variety of scales, ranging from basin-scale to well-scale. Regional and field-scale mapping will use traditional geologic data sets, while well-scale data will come from core analyses and new, high resolution borehole imaging logs.

            Fractures play many roles in carbonate reservoirs. They may serve as principal storage in very tight matrix rocks, or greatly enhance permeability in conventional intergranular or intercrystalline reservoirs. Fractures may also be instrumental in the creation of reservoirs by providing fluid conduits for diagenetic processes. Several significant Michigan carbonate reservoirs have been formed by fracturing and dolomitization of very tight limestones. These fields occur in Ordovician through Devonian age rocks and have produced in excess of 150 million barrels of oil.

            Better understanding of the origin, development and distribution of fracture systems in carbonate rocks will allow for more efficient exploitation of these type of reservoirs and provide an exploration paradigm for future development of new reservoirs in presently undeveloped areas.

A New GIS Compilation of “Final Report GRI92-0391/Illinois Basin Studies 2: Gas Potential of New Albany Shale (Devonian and Mississippian) in Illinois Basin”

HASENMUELLER, NANCY R., JOHN B. COMER, PAUL N. IRWIN, KIMBERLY SOWDER, CHARLES W. ZUPPANN, and JEANNE CARPENTER, Indiana Geological Survey, Bloomington, IN; DAVID MORSE, Illinois State Geological Survey, Champaign, IL; BRANDON C. NUTTALL, Kentucky Geological Survey, Lexington, KY; and DAVID G. HILL, Gas Research Institute, Chicago, IL

            Information from the 1994 Gas Research Institute/Illinois Basin Consortium report on the gas potential of the New Albany Shale (Devonian and Mississippian) in the Illinois Basin is now available in an entirely digital format. The text, figures, tables, and references from the out-of-print original report are available in an Adobe Acrobat file. Records of the wells (>5,000) used to produce this report are available in a Microsoft Access database which includes UTM X, UTM Y, well permit number information (identification number), New Albany Shale top (elevation), and New Albany Shale thickness. Map plates (scale of compilation: 1:1,000,000), originally in AutoCAD format, are now available as GIS coverages. The GIS coverages include the following layers: (1) elevation of the top of the New Albany Shale; (2) thickness of the New Albany Shale; (3) average initial potential (IP) for the New Albany Shale gas fields; (4) mean random vitrinite reflectance (o) for the New Albany Shale; and (5) locations of cores of the New Albany Shale. Stratigraphic cross sections illustrating the distribution of the New Albany Shale members in the three-state area are included as a TIF raster image.

            Digital data for nonconfidential New Albany wells obtained from 1991 through 1997 are also included in the new compilation. Data for New Albany Shale cores obtained from 1991 through 1997 are included in a GIS database. A list of New Albany Shale articles published since 1991 is included as an Acrobat PDF file. The complete electronic files/coverages with metadata are available on CD-ROMs from the Illinois State Geological Survey, Indiana Geological Survey, Kentucky Geological Survey, and Gas Research Institute.

An Integrated Geological and Engineering Study of St Peter Sandstone Gas Storage Reservoir at the Hillsboro Field

HUFF, BRYAN G., Illinois State Geological Survey, 615 E. Peabody Drive, Champaign, IL 61280

            This study investigated the geology of the Hillsboro Gas Storage field and incorporated the information in an integrated computerized reservoir model. Petrophysical analyses reveal four distinct flow units in six cored wells. These flow units corresponded to four lithologies. Distributions of petrophysically-derived flow units show considerable vertical variability but lateral continuity. This explains why it has been easier to develop the gas bubble laterally than vertically.

            A three-dimensional reservoir model was used to understand the past behavior of the Hillsboro Gas Storage Field and to investigate the field's performance under various development scenarios. Key issues examined after successful history matches of the past gas storage performance included (1) the maximum possible total gas-in-place volume without gas loss and (2) the optimum base load volume that permits the achievement of the peak-day rate requirements.

            The results from simulated development strategies suggest that increasing the field's total gas-in-place volume would cause gas to migrate beyond the east, north and west observation wells. They also suggest that storage enlargement through gas injection into the lower layers may not prevent gas migration. Simulated gas deliverability results suggest that a peak day rate of 150 Mmscf/D can be achieved with up to 80% of the working gas produced before the peak day and that the peak day rate would fall below 125 Mmscf/D when 85% or more of the working gas is produced before the peak day. The addition of strategically located new wells would boost the simulated gas deliverability.

Late-Middle Eocene Healing Phase Deposition in the Gulf Coastal Plain

HURLEY, JOHN V. and RICHARD FLUEGEMAN, Geology Department, Ball State University, Muncie, IN 47306

            A Healing Phase Unit is recognized and the stratigraphic position of the time-stratigraphic condensed section is identified, through a refinement of the sequence stratigraphy, of the Mossy Grove Core’s late middle Eocene biostratigraphic interval Planktonic Foraminiferan Zone P14. P14 in this western Mississippi core, restrained to the core depth interval from 512 to 408 feet, is represented by the Moody’s Branch Formation and the overlying lower portion of the Yazoo Clay, two classical and eustatically significant Gulf Coastal Plain units. The refined sequence stratigraphy is such that the 12 feet of Moody’s Branch are Progradational Transgressive deposits, the lowest 78 feet of Yazoo Clay is a Healing Phase Unit, and the remaining 14 feet of P14 Yazoo Clay are Highstand Regressive deposits. The condensed section separating the underlying Transgressive Systems Tract from the overlying Regressive deposits occurs at the core depth of 422 feet.

            Ratios of planktic to benthic foraminifera, a relative paleobathymetric proxy, were determined from samples collected every two feet. A higher ratio would be implicit of relatively deeper water as planktics would be correlatively more prevalent under such conditions. The overall larger trend of the data collected from this exercise is a cycle which increases from zero to a maximum of 0.21 at the core depth of 422 feet and then decreases throughout the remainder of the section. The occurrence of the maximum planktic : benthic ratio, at 422 feet, was used to identify the stratigraphic position of the condensed section, the sequence stratigraphic unit representative of maximum sea level within a transgression-regression cycle.

            Identification of the condensed section at 422 feet places the lower 78 feet of Yazoo Clay within the Transgressive Systems Tract. This assertion, which is not corroborated by literature references to the condensed section in the Moody’s Branch Formation, is reconciled by the identification of this lower 78 feet of Yazoo Clay as a Healing Phase Unit. The argument that this unit is from a Healing Phase is supported by its existence within the Transgressive Systems Tract, its occurrence above coarser grained progradational deposits, the paleoecological setting in which it was deposited, as implied by its Uvigerina-Bulimina benthic foram assemblage, and the existence of a Type I Sequence Boundary below the entire sequence, suggestive of a prior regression that would have produced a basin conducive to Healing Phase development.

Managing for Oil and Overcup Oaks

JACQUART, ELLEN M., The Nature Conservancy, Indianapolis, IN

            The Nature Conservancy has purchased a number of tracts in southwest Indiana which feature oil wells in addition to high quality natural communities and rare species. Saunders Woods in Gibson County and Twin Swamps in Posey County are examples of lands with significant ecological features purchased by The Nature Conservancy which are underlain by oil, and have mineral rights owned by another party.

            Sanders Woods is an 880-acre tract containing the largest wet-mesic old growth forest left along the lower Wabash River; it also contains nine producing oil wells. Twin Swamps is a 600-acre preserve initially purchased by The Nature Conservancy and transferred to the Department of Natural Resources - Division of Nature Preserves, who now owns and manages it. Twin Swamps is named for its two wetland communities: an overcup oak slough and a bald cypress slough. This preserve also had several producing oil wells, but a cooperative project with the oil well operators resulted in closing the wells. The challenges and opportunities involved in managing these old growth forests and cypress sloughs in harmony with oil extraction operations will be discussed.

Depositional Systems Analysis – Key Element in Affordable Assessment of Groundwater Availability and Pollution Potential in the Glaciated Appalachian Region of Eastern New York State

JOHNSON, KENNETH G., Dept. of Geology, Skidmore College, Saratoga Springs, NY

            Development associated with expansion at the northeast margin of the New York State Capital District is significantly impacting groundwater aquifers of small communities which rely entirely on shallow, individual-dwelling wells, most of which produce from facies of the Hoosic Delta, a small late Pleistocene system that prograded into glacial Lake Albany. Ironically, those qualities which make these facies such good aquifers are also qualities which make them very susceptible to contamination by landfill leachate, leaking underground storage tanks, agricultural fertilizer infiltration and malfunction of poorly designed and located septic systems. These rural townships and villages are experiencing a high percentage increase in housing starts, have very low tax bases and are hard pressed to find the money required to cope with the rapid transition from rural to suburban mode. They need geoscience information and appropriate technology not unlike that needed by developing nations around the world. As an example of low cost applied sedimentology in support of planning efforts, this paper outlines the results of facies analysis of the Hoosic Delta depositional system and how this information can be used by planners who are concerned about groundwater availability and pollution potential. It is worthy of note that this kind of depositional systems modeling originated in the petroleum industry and now has, or should have, wide application in the environmental geosciences.

Preliminary Conodont Biostratigraphy of the Salina Group (Silurian) of the Northern Indiana Subsurface and Recognition of the Wenlock/Ludlow Boundary

KLEFFNER, MARK A., Dept. of Geological Sciences, The Ohio State University at Lima, Lima, OH; and CARL B. REXROAD,

Indiana Geological Survey, Bloomington, IN

            Previous attempts to determine a conodont biostratigraphy for the Salina Group in the northern Indiana subsurface have been hampered either by a paucity of conodonts, scarce representation of diagnostic conodonts, or a lack of a reasonably high-resolution Silurian conodont biostratigraphy to correlate with. Restudy of hundreds of conodont samples processed from Salina Group cores from northern Indiana during the 1960's and early 1970's

indicates that although diagnostic conodonts are scarce, they do provide enough data for at least a preliminary, somewhat generalized biostratigraphy and correlation with high-resolution Silurian conodont biostratigraphies recently developed. Kockelella variabilis is first represented in most cores near the middle of the Louisville Member of the Pleasant Mills Formation,

likely indicating that the Wenlock/Ludlow boundary is within the Louisville. This is the same level at which the first representatives of that species also occur in the Lego Member (= Louisville) of the Wayne Formation of central Tennessee. The first representatives of Ozarkodina remscheidensis eosteinhornensis occur in the Wabash Formation, indicating that the formation is within the upper part of the Ludlow to Pridoli. Distribution of diagnostic conodonts in the Salina Group may provide enough data for graphic correlation of several of the core sections with a recently revised conodont- and graptolite-based Silurian chronostratigraphy, resulting in an even more precise correlation for those strata than is possible at present.

Geology of the Council Run Gas Field, North Central Pennsylvania: Implications for Energy Resource Development in the Eastern Plateaus Province of the Central Appalachian Basin

LAUGHREY, C. D., Pennsylvania Geological Survey, Pittsburgh, PA; D. A. BILLMAN, Consultant, Mars, PA; and M. R. CANICH, Statoil, Alexandria, VA

            Council Run field in north central Pennsylvania is enigmatic because it lies near the eastern edge of the Appalachian Plateau where many potential reservoir rocks have low porosities and permeabilities. Source rocks are postmature. Reservoir sandstones at Council Run, however, have porosities as high as 16%, gas saturations up to 83%, and EUR's exceeding 1.0 bcf in some wells. δ¹³C and δD of the produced gases indicate an oil-associated accumulation.

            The principal reservoirs at Council Run are Upper Devonian in age. They occur within a fourth-order type 1 stratigraphic sequence. Sandstone stacking patterns define lowstand, transgressive, and highstand systems tracts. Productive sandstones are lithic to highly feldspathic with hybrid pore textures comprised of reduced primary intergranular voids and secondary oversized fabric-selective voids. Early petroleum emplacement helped to preserve primary pores.

            The Burket Member of the Harrell Formation and the Marcellus Formation are probable sources of the gases. The generative potential of these rocks is exhausted, but geochemical data suggest that these black shales originally contained oil-prone kerogens that generated liquid hydrocarbons in the past. The isotope chemistry of gases produced at Council Run implies that they are mixtures of 1) hydrocarbons generated by primary cracking of kerogens while the source rocks resided within the oil window and 2) gases generated by secondary cracking of oil during deeper burial of the Devonian strata. Modeling of burial and petroleum migration history in the subsurface rocks of the region helps to constrain the timing of petroleum accumulation in the field.

Trials, Tribulations, and Potential of Using 3-D Geologic Visualization for Subsurface Reservoir Characterization

Leetaru, Hannes E., Illinois State Geological Survey, Champaign, IL.

            Three-dimensional digital modeling can substantially improve reservoir characterization. The 3-D workstation is the only effective way of observing the spatial relationships of all of the reservoir attributes, from geologic facies to porosity and permeability. No other technology allows a researcher to visualize potential fluid pathways by delineating the lateral and vertical continuity of higher permeability beds. This same 3-D model can be used by a geologist to determine which wells have penetrated high permeability beds and whether these beds have been perforated in the well.

            The modeling software cannot be used as a black box into which data are dumped and from which the relationship of different reservoir attributes such as facies and porosity become readily apparent. A critical step is normalizing the data. Wireline logs such as gamma ray and spontaneous potential curves do not have an absolute scale and must be normalized to each other. Calibration errors in the density and neutron logs should be corrected. Incorrect wireline logs or core data typically show up as stripes or hot spots in a 3-D model.

            The stratigraphic framework must be well understood before modeling can begin. With contour mapping of reservoir attributes in two dimensions, errors such as the crossing of stratigraphic horizons are not always obvious; but in three dimensions interpretation errors produce an impossible geologic model of the subsurface. With 3-D visualization, the geologist is forced to use an iterative approach to mapping, whereby errors are found and corrected. Two-dimensional mapping by itself is no longer adequate for characterizing a subsurface reservoir.

Coalbed Methane Production of the Buck Knob Anticline Field, Wise County, Virginia

LEWIS, RICHARD T., Equitable Production Company, Kingsport, TN

            The Buck Knob anticline of Wise County represents the southwestern extent of coalbed methane production in Virginia. The anticline at depth is a ramp structure developed as a result of overthrusting of the Devonian Shale during the Alleghanian orogeny. Approximately 400 feet of structural closure is expressed at the Pennsylvanian level.

            Numerous temperature anomalies and natural gas shows (5-620 MCFPD) were encountered while drilling and logging through the coal section. Reservoirs belong to the Norton and Lee Formations (Morrowan) and range from 650-2450 feet in depth. The coals are of high volatile A to medium volatile bituminous rank. Gas contents range from 60-150 scf/ton. A typical completion contains 6 coal seams with an aggregate thickness of 120 inches. Stimulation is achieved through single stage limited entry fracture treatment.

            Average open flow is 50 MCFPD. Average peak rate is 95 MCFPD and is reached within 9-12 months. Exceptional wells have production rates above 200 MCFPD. Current field rate exceeds 1500 MCFPD. Estimated ultimate recoveries are 425 MMCF per well based on 80 acre spacing. Total field recoveries are expected to reach 25-30 BCF.

            The field serves as an analog for low rank/low gas content coals producing at economic rates due to enhancement of permeability by natural fractures.

Relationship of Subsurface Distribution and Thickness Patterns of Carboniferous Rock Units to the Structure of the La Salle Anticlinorium, Lawrence County, Illinois

LUMM, D. K., Kentucky Revenue Cabinet, Frankfort, KY

            Distribution and thickness patterns of an interval of Carboniferous rock units from the Beech Creek ("Barlow") Limestone of the Pope Group (Mississippian) to the Springfield Coal Member of the Carbondale Formation (Pennsylvanian) in Lawrence County, Illinois were mapped in order to determine the effect of structural control of the southern part of the north-northwest trending La Salle anticlinorium, Illinois basin, during deposition of these units. Data from 720 geophysical logs from a 170mi² (350 km²) area were used to produce a network of cross sections and distribution and thickness maps. Abrupt westward thickness increase of "sandstone B", an informally named unit of the Caseyville Formation, west of the hinge line of the anticlinorium suggests a depositional response to uplift of the La Salle anticlinorium or basinal subsidence. A significant thinning of "sandstone C", an informally named unit of the upper part of the Caseyville Formation across the axis of the Bridgeport anticline suggests antiform development during the latter part of Caseyville deposition. The abrupt thickness changes, discordant dips, and linearity of these sandstone units, as well as the juxtaposition of erosional valleys that truncate Pope Group units suggests the presence of small offset (less than 10 feet or 3 m) faults that outline an ancestral structural block which is coincident with the Bridgeport anticline. An enigmatic problem is the apparent lateral continuity of the Tar Springs Sandstone (Pope Group) and "sandstone A", the basal unit of the Caseyville Formation in part of the study area. The uncertain correlation of "sandstone A" precludes the exact placement of the Mississippian-Pennsylvanian unconformity and the timing of corresponding structural events.

Solving Environmental Problems With Petroleum Geology Principles- A Kentucky Case Study

MAY, MICHAEL T., Dept. of Geography and Geology, Western Kentucky University, Bowling Green, KY

            An important aspect of site characterization at any site with negatively impacted groundwater, soil or rock is understanding regional geology. More specifically, understanding structural position, facies changes, sequence stratigraphic framework, petrophysical variation and source rock characterization of hydrocarbons in the vicinity of a petroleum contaminated site is a requisite. Many large sites (several hundred acres), as are typical of military installations, have petroleum contaminated groundwater and earth materials. Furthermore, some of these sites are located within or immediately adjacent to oil-producing basins possessing relatively shallow producing horizons. Differentiating between anthropogenic and natural sources for benzene, toluene, ethyl benzene and xylene at such sites may be difficult if thorough site characterization is not conducted. The Lexington-Bluegrass Army Depot, located near the crest of the Cincinnati Arch in Kentucky, is a good example of inherent difficulties associated with identification of contaminant sources. At this site, the Ordovician Lexington Limestone contains aquifers that are punctuated by multiple marine flooding surfaces and a sequence boundary. The Lexington penetrated by drilling at the site can be divided into the Millersburg, Tanglewood (Upper and Lower Tongues), and Grier members. The Grier is further separated by flooding surfaces which, are mainly shale-rich beds. Primary aquifers at the site can be mapped as physically separated and chemically partitioned into high salinity and low salinity hydrostratigraphic units with quite different contaminant constituents.

Outcrop and Subsurface Evaluation of Chesterian and Basal Pennsylvanian Sequences in Western Kentucky

MAY, MICHAEL T., Dept. of Geography and Geology, Western Kentucky University, Bowling Green, KY

            The Brownsville paleovalley in Edmonson County, Kentucky and the Evansville paleovalley in southwestern Indiana are but two examples of major valley systems associated with development of the Kaskaskia-Absaroka Sequence Boundary in the Illinois Basin region. Other workers have produced subcrop maps of the Mississippian-Pennsylvanian unconformity surface in Illinois, Indiana and Kentucky. Little regional work elucidating the detailed nature of tributary valley systems however, has been completed in Kentucky. Correlation of the outcrop with mostly electrical logs from the outcrop belt along the Brownsville paleovalley and into the subsurface of Butler, Edmonson, Grayson, Ohio and Warren counties shows the dissected nature of the pre-Pennsylvanian surface. Local relief mapped along this sequence boundary commonly exceeds 30 meters, particularly in the lower reaches of tributary valleys proximal to trunk systems. Preliminary petrographic work on rocks in this area has revealed feldspar and fine-grained sedimentary rock fragments to be more abundant in Chesterian siliciclastics versus basal Pennsylvanian siliciclastics. Outcrop investigation of Pennsylvanian and Chesterian sandstones suggests several depositional environments ranging from fine-grained tidally influenced channel deposits to coarse-grained, bedload dominated fluvial systems. Future work will entail establishing petrofacies characteristics versus environments of deposition and well-log signature to better aid in differentiating Chesterian and basal Pennsylvanian sandstones in problematic areas.

Precambrian "Seismic Stratigraphy" Beneath the Illinois Basin

McBRIDE, JOHN H., Illinois State Geological Survey, University of Illinois, at Urbana-Champaign, 615 East Peabody Drive, Champaign, IL 61820

            Reprocessing of regional seismic reflection profiles reveals multiple Precambrian "stratigraphic" sequences beneath the Paleozoic Illinois Basin. Three-dimensional mapping of this reflectivity using an open network of profiles indicates a broad basinal sequence ("Centralia sequence") that reaches a maximum depth of about 10 km and a thickness of 6 km (from generalized traveltime-to-depth conversion). The internal structure of this sequence is marked by dipping and offset reflectors, and widespread apparent unconformities. The regional structure of the sequence is well developed with discrete western and southern boundaries along which the sequence pinches out beneath the base of the Paleozoic section. Two additional Precambrian sequences are present beneath the Centralia sequence and both appear to be areally more restricted. The upper poorly reflective sequence (maximum depth, about 17 km) is underscored by an extremely bright reflection; a second reflective package, structurally beneath the former, is marked by abrupt offsets that may be related to an ancient syn-rift sequence. At this stage of our understanding, more than one hypothesis is possible for the origin of the Precambrian reflectivity, including basaltic flows or sills interlayered with clastic sediments and/or emplaced within the basement granite-rhyolite terrane. These sequences may represent older Keweenawan-type rift-related volcanism and sedimentation, which cut through the northern Midwest and Lake Superior.

Availability of The Upper Freeport (No. 7) Coal in Eastern Ohio

McDONALD, JAMES; and MARK E. WOLFE, Ohio Division of Geological Survey, Columbus, OH

            The Ohio Division of Geological Survey, in cooperation with the U.S. Geological Survey, has completed a GIS-based investigation on the availability of the Upper Freeport (No. 7) coal in Ohio. Previous coal availability investigators in Ohio conducted detailed computer-based studies of all mineable coals at the 7.5-minute-quadrangle scale. This investigation is the first attempt to determine the amount of coal from a single bed available for mining statewide.

            Two types of data were compiled and computerized: (1) line and area data from maps, such as coal croplines and mined-out areas, and (2) point data, such as drill-hole descriptions and measured sections. Digital maps of coal structure, thickness, abandoned surface and underground coal mines, cropline, and overburden were generated. Digital maps of land-use activities which may restrict mining (urban areas, highways, state parks, etc.) were modified from Ohio Department of Transportation digital files. A personal-computer-based geographic information system was used to perform the resource calculations.

            The accuracy of GIS-derived values for original coal-resources was verified by comparing the results to earlier coal-resource investigations in Ohio and to an ongoing coal-assessment study by the U.S. Geological Survey. The methodology will be applied to other significant coal beds in Ohio so that an accurate estimate of the total available coal statewide can be made. It is hoped this information will enhance future land-use decisions.

Using Building Stones As A Teaching Tool

MIRSKY, ARTHUR, Dept. of Geology, Indiana University-Purdue University Indianapolis, Indianapolis, IN

            The Department of Geology at IUPUI has developed a self-directed walking field trip that uses building materials in downtown Indianapolis as a substitute for seeing geologic features in the natural field setting. A surprisingly large number of varied geologic features can be seen in these building materials. Among igneous rocks, one can see anorthosite, basalt, diorite, gabbro, granite, granodiorite, larvikite, monzonite, obsidian, pumice, and scoria. Among sedimentary rocks are breccia, chert, dolostone, limestone, sandstone, and travertine. Among metamorphic rocks are gneiss, marble, quartzite, and schist. Recognizable minerals include biotite, calcite, hematite, hornblende, jasper, limonite, olivine, orthoclase, plagioclase, quartz, and serpentine. Human-made building materials include aluminum, brass, brick, bronze, cement, concrete, glass, pebble aggregate, and tile. Igneous textures range from glassy, fine- to coarse-grained to porphyritic; igneous structures include segregation zones, dikes, flows, and inclusions. All sedimentary textures are present except natural conglomerate; sedimentary structures include parallel bedding, several types of cross-bedding, laminations, graded bedding, stylolites, flagstone, and trace fossils. Fossil fragments are abundant as fossil hash, and recognizable fossils include several types of bryozoans, crinoid stems, brachiopods, and snails. Metamorphic textures include both foliated and massive; metamorphic structures include schistose, flow, and gneissose. Both physical (mechanical) and chemical weathering are abundantly represented. This Indianapolis field trip guide includes all of the buildings in the selected blocks on the street, unlike guides for other metropolitan areas that emphasize particular prominent buildings. The main shortcoming of this building-material field trip is that some aspects of introductory geology are not represented (such as landscape development, glaciation, mountain building). Also, of course, no one should take a hammer on the walking tour and attempt to collect samples.

Low Altitude Airborne Multispectral Microfracture Analysis in the Control of Oil and Gas Production, Coalbed Methane and Site Location of Directional Drilling.

MOORE, BRUCE R., Dept of Geology, Univ of KY, Lexington, KY; and PETER R. MOORE, Geo-Flite Pty Ltd, Melbourne, Australia.

            Detection of high resolution microfracture or rock jointing is achieved by the generation and advanced computer analysis of low altitude airborne multispectral image data to plot joint patterns through soil and vegetation cover and determine high density targets. The microfracture and joint systems have been shown to control the migration of fluids and gases in the rocks and their location is vital to establishing economic primary and secondary production. The same data enables the efficient dewatering of coalbed methane prior to production and the successful location of directional drilling to intersect maximum fracture porosity, both in exploration and also development drilling. The method is unique in the world and has been very successful in exploration in the USA, Canada and Australia.

Fluvial-deltaic Architecture of the Mississippian Tar Springs Sandstone, Illinois Basin

MORSE, DAVID G., Illinois State Geological Survey, Champaign, IL

            The Mississippian Tar Springs Sandstone, a cratonic fluvial-deltaic sequence, was deposited from north to south as one cycle in a rhythmic carbonate/siliciclastic package that is typical of the Chesterian in the Illinois Basin. Formation and net sand isopach maps and detailed cross-sections indicate a regional architecture consisting of distributary channels which form composite sand bodies up to 125 feet thick, 1 to 2 miles wide and interfluves of shaley fine sand and silt. The channel bases cut downward into older Tar Springs, delta fringe fine sands and shales, and the underlying Glen Dean Limestone. These stacked channel sands are concentrated regionally in sinuous, north-south oriented paleovalley-fills or fluvial channel systems 6 or 8 miles wide and can be correlated north-southward for up to 100 miles. Tidal rhythmites have been observed in fine sands and silts in Indiana. Other tidal indicators have been observed at the southern most extent of the Tar Springs, along sandstone outcrops near Alto Pass, Illinois. Above the stacked sandstones are intertidal to supratidal, interbedded fine sands and silts, and then shales with local coaly stringers, which are capped by the thin, widespread, shallow marine, Vienna Limestone.

            The Tar Springs was deposited as a southward prograding deltaic sedimentary package. Tidal processes are believed to have reworked the fluvial channel deposits found near the mouth of the delta. The heterogeneous nature of the formation contributed to the formation of stratigraphic hydrocarbon traps in the Illinois Basin. Knowledge of Tar Springs sand body architecture will thus improve the search for new fields and lead to a better understanding of existing ones.

Naturally-Occurring Petroleum Hydrocarbons in Indiana Glacial Till

MUNDELL, JOHN A., Mundell & Associates, Indianapolis, IN; ANDREW GREMOS, Keramida Environmental, Inc., Indianapolis, IN; JOSEPH ARNOLD, Indianapolis Department of Public Works, Indianapolis, IN

            This presentation documents the finding of detectable levels of naturally-occurring petroleum hydrocarbons in Indiana glacial till during the investigation of a site impacted with other organic chemicals. Significant excavation and removal of soils off-site necessitated the evaluation of the soils for waste disposal options. Initial testing of fill and glacial till at the site indicated widespread detectable total petroleum hydrocarbon (TPH). Additional investigation using microscopic observations and downhole geophysical logging indicated that the TPH in the glacial till was the result of the presence of New Albany shale fragments within the till matrix. Analytical testing of the soil using GC/FID by U.S. EPA Method 88015 (Modified) indicated a chromatographic signature that was different between impacted soils and naturally-impacted soils. A statistical methodology was used to determine the grouping of the samples into two distinct populations. Using these techniques, soil with naturally-occurring TPH as a result of the New Albany shale was able to be differentiated from other soils impacted by past dumping on the site. Substantial disposal cost saving will be realized as a result of this study.

Natural Attenuation of Petroleum Hydrocarbons in a Prolific Outwash Sand and Gravel Aquifer

MUNDELL, JOHN A., Mundell & Associates, Indianapolis, IN; JAMES A. BERNDT, Mundell & Associates, Indianapolis, IN; JOSEPH ARNOLD, Indianapolis Department of Public Works, Indianapolis, IN

            The Indianapolis Department of Transportation’s West Street Maintenance Facility is located within 400 ft of the White River near downtown Indianapolis. Beneath the facility, extensive sand and gravel outwash deposits are present which allow rapid groundwater movement and subsequent discharge to the River. Detection of a release of petroleum hydrocarbons from five underground storage tanks in 1990 prompted a multiphase investigation of the release and documentation of the full extent of the groundwater plume with a comprehensive monitoring well network. Since the detection of the release, eight years of groundwater monitoring data have shown the extent of the plume has stabilized and never reached the river despite significant groundwater velocities. In addition, plume concentrations of benzene, toluene, ethylbenzene and xylene have decreased over time without active remediation occurring other than the initial storage tank and associated soil removal, and limited free-product removal from monitoring well bailing activity. As part of a Corrective Action Plan (CAP) submittal to the Indiana Department of Environmental Management, a comprehensive area groundwater flow model coupled with two-dimensional chemical transport modeling were used to evaluate chemical degradation rates and to predict the expected concentration declines as a result of the original source removal and biodegradation. The modeling results suggested that an additional 2 to 3 years of monitoring data would confirm that natural attenuation was stabilizing and reducing the plume size. This evaluation supported a “no action/monitoring only” corrective action plan that continues to document the effectiveness of natural attenuation as the remediation alternative of choice.

Common Sources of Errors in Coalbed Gas Resource and Reservoir Gas-In-Place Values

NELSON, CHARLES R., Gas Research Institute

Coalbed reservoirs in the U.S. contain an estimated 695 trillion cubic feet (TCF) of natural gas resources, hold 14% (146 TCF) of the total recoverable U.S. natural gas resources, and currently account for 5% (1.0 TCF) of total annual U.S. natural gas production. Accurately determining the initial gas-in-place volume is a crucial element of coalbed gas resource and reservoir evaluation. However, different reservoir property analysis method often yield very different gas-in-place values. This paper present results from evaluations of the accuracy of commonly used reservoir property analysis methods. Quantitative data for five commonly encountered sources of error will be presented. These errors are: (1) using a too low maximum density limit when using density log data to determine the gross reservoir thickness, (2) using a too low value for the average reservoir rock density, (3) basing the in-situ gas content on gas desorption data collected at ambient surface temperature conditions, (4) basing the in-situ gas content on gas desorption data collected from drill cuttings, and (5) basing the in-situ gas content on the assumption that the residual gas volume value is negligible. These commonly used analysis practices can result in large (50% or greater) underestimation error in the gas-in-place value and, in turn, the cumulative gas recovery predicted by reservoir simulation methods. Because these reservoir property analysis practices have been so widely used in the past, significant potential may exist for large gas resource and recoverable reserve estimate gains in many existing coalbed gas fields.

GPR for Environmental Site Investigations: The Importance of Polarization

RADZEVICIUS, STANLEY, J., DANIELS, JEFFREY, J., GUY, ERICH, D.

Department of Geological Sciences, The Ohio State University, Columbus, Ohio 43210

            Ground penetrating radar (GPR) is a geophysical technique that uses electromagnetic waves in the radio frequency range to investigate geologic, engineering and hydrogeologic features. Radar waves are produced by a transmit antenna, scattered from interfaces between media having contrasting intrinsic impedances, and recorded by a receive antenna. Electromagnetic waves can be described by the orientation of their electric and magnetic fields, and the direction of propagation. Polarization refers to the magnitude and orientation of the electric field as a function of time and space.

            The polarization of the measured GPR signal is a function of the transmit antenna and the depolarization properties of scattering targets in the subsurface. The reflection coefficients of buried objects and stratigraphy are a function of the incident polarization and this makes polarization useful for defining the size, shape, orientation, and material properties of buried objects. Polarization knowledge is important for survey design, imaging, interpretation of data, and reduction of clutter.

            Co-pole antennas are useful for measuring energy scattered from both non-depolarizing and depolarizing objects while crossed dipole antennas are useful for imaging depolarizing targets, as well as targets which scatter cross-polarized components that were present in the incident field. Co-pole and cross-pole configurations can be used to discriminate between the back scattered fields from flat planes that are not depolarized and those of long circular cylinders that are strongly depolarized. The best choice of antennas and polarizations for use in a particular survey depends on the targets of interest and the field conditions

Conodont Paleontology of the Lead Creek Limestone Member of the Mansfield Formation (Pennsylvanian) in Indiana

REXROAD, CARL B., Indiana Geological Survey, Bloomington, IN; LEWIS M. BROWN, Lake Superior State University, Sault Ste. Marie, MI, and NATHAN A. WILKE, Kansas Geological Survey, Lawrence, KS

            The study of the Lead Creek Limestone Member (of the Mansfield Formation), herein recognized as Atokan, was designed to test for geographic continuity of deposition, possible time transgression, and paleoenvironmental variation as well as for age determination. Compilation of a conodont zonation for the Pennsylvanian rocks of the Illinois Basin will be an important reference for comparison with other areas of the world.

            The Lead Creek is readily recognizable on outcrop in Hancock County, Kentucky, and in Spencer, Perry, and Dubois Counties in southern Indiana and in the immediately adjacent subsurface area to the west and north. It consists of two named dominantly limestones beds, the Fulda Bed below and the Ferdinand Bed above, and a shaley interval between, except that to the north generally only a single ledge of limestone is present in the Lead Creek position. The Fulda commonly is a dark, dense, argillaceous and shaley limestone, and the Ferdinand a light colored, fine-grained, cherty limestone. The shale and siltstone unit between them contains thin coal and paleosol in places. We interpret the environment of deposition as shallow, but open sea for the limestone and shoal to nonmarine conditions for the middle unit.

            The Lead Creek conodont fauna is of low diversity and is dominated by Idiognathodus and Idiognathoides. Hindeodus, Neognathodus, and Diplognathodus are minor elements. The presence of Idiognathoides and Neognathodus atokaensis distinguishes the fauna from that of the next overlying named carbonate unit, the Desmoinesian Perth Limestone Member of the Staunton Formation. At present it is not possible to correlate the Lead Creek with any of the minor marine intervals in its approximate position in Illinois.

Proof of Natural Attenuation: Comparison of Evaluation Criteria

REYNOLDS, ROBERT K., Quality Environmental Professionals, Inc., Bloomington, IN; BERNARD A. LAUCTES, Quality Environmental Professionals, Inc., Indianapolis, IN

            Natural attenuation is the reduction of contaminant concentration or toxicity resulting from dispersion, dilution, biodegradation, volatilization, sorption, and other processes that occur naturally in the subsurface. The concept and use of natural attenuation is gaining in popularity in this new era of evaluation and remediation based on the risks posed by contaminants to human health and the environment.

            State and federal program documents and other non-regulatory guidance documents recommend the evaluation of various chemical and biological parameters in soil and groundwater to indicate the occurrence of natural attenuation of petroleum hydrocarbons. The US Environmental Protection Agency, the American Society for Testing and Materials’ Risk-Based Corrective Action standard, the Air Force Center for Environmental Excellence and the state programs all recommend common parameters, such as dissolved oxygen, nitrate, sulfate, and fraction of organic carbon, to indicate the presence of aerobic and anaerobic conditions in the subsurface.

            Each guidance document identifies other evaluation criteria that may be useful based on that program’s attenuation model. This presentation will provide a brief overview of the natural attenuation process, identify the evaluation criteria from each program, and recommend a basic list of evaluation that should be appropriate for most sites.

Regional Middle Run Formation Thickness Distribution as Determined by Potential Field Analysis: A Foreland Basin to the Grenville Front?

RUPP, JOHN A., Indiana Geological Survey, Bloomington, IN; VLADIMIR P. RYBAKOV, Geological Sciences Department, Indiana University, Bloomington, IN; ALEX R. ZLOTIN, Indiana Geological Survey, Bloomington, IN

            The regional distribution pattern for the pre-Mount Simon Sandstone (late Cambrian) sedimentary rock sequence, here referred to as the Middle Run Formation, in an area centered about Indiana is interpreted to represent a series of linked sub-basins that formed immediately proximal to the Grenville orogen. Potential field analysis, utilizing relationships of signal intensity to sediment thickness, yields a complex pattern of small localized accumulations of thick sediment interpreted to be depocenters controlled predominantly by preexisting and syndepositional basement faulting. Distribution patterns were primarily derived from the observed linear relationship between gravitational and magnetic intensity and thickness established in a series of structural cross sections that depict sediment thickness as constrained by seismic data. The correlation coefficient in the observed relationship approached 0.7. Assumed density values for these sediments used in the cross sections are consistent with densities for these rocks as measured in boreholes using density geophysical logging.

            Calculated thicknesses were found to exceed 15,000 feet in some localities while rapidly decreasing to near zero over basement highs. The overall regional pattern in both thickness and areal extent is supportive of a complex basin history that may have initiated as a dominantly tensional system of linked grabens and half-grabens, and evolved to become a fragmented foreland basin system where individual sediment accumulations were controlled by transtensional or oblique slip faults associated with the closing phases of the compressive Grenville collisional tectonism.

Kentucky Geological Survey—A Resource for Teachers

RUTHVEN, CAROL L. and STEPHEN F. GREB*, Kentucky Geological Survey, University of Kentucky, Lexington, KY

            Public outreach and technology transfer are essential to the mission of the Kentucky Geological Survey (KGS). Of significant import is our multifaceted educational outreach program. KGS provides numerous publications and data sets concerning geology in Kentucky that are useful for teaching K–12 core concepts. KGS participates in national and state science-teacher conferences, state and district science-teacher workshops, collaborates with other organizations to provide information for their science-teacher workshops, hosts regional field trips in conjunction with the Kentucky Society of Professional Geologists, provides tours for school groups at KGS, visits more than 100 classrooms annually, and provides volunteer judges for local, regional, and state science fairs.

            Much of our educational outreach has been achieved by continuously expanding and updating the resources on our award-winning Web site at www.uky.edu/KGS/home.htm. The Earth Science Education Network is part of this site. Much of the success of the network is due to the interaction between KGS staff and educators in Kentucky. The network provides: (1) annotated links to other sites that provide information for teaching K–12 core concepts, (2) an earth-science-educator listserv to help earth-science teachers communicate with each other and professionals, (3) classroom activities created by KGS staff, educators in Kentucky, and links to classroom activities offered elsewhere on the Internet, (4) fact sheets and interesting stories about Kentucky geology, (5) lists of earth-science volunteers and places to visit in the State, (6) a calendar of earth-science events, and (7) a summary of the geology of Kentucky. Sections on the fossils and rocks and minerals of the State are also very popular.

Recent Discoveries Renew Interest in the Prolific Geneva Dolomite (Middle Devonian), West-Central Illinois Basin

SEYLER, BEVERLY, and JOHN P. GRUBE, Illinois State Geological Survey, Champaign, IL

            The Geneva Dolomite, a basal member of the Middle Devonian Grand Tower Formation in the Illinois portion of the Illinois Basin, is an exploration target that has recently generated much interest. Wells from fields discovered in the 1990s have initial production rates exceeding 300 barrels of oil per day from depths of 3000 to 4000 feet. Cumulative production from some of these wells is greater than 100,000 barrels in approximately two years. A study in Marion, Fayette and Effingham counties, Illinois, shows that pronounced closure, fracturing, and development of secondary porosity, including dolomitization and solution enhanced moldic porosity, are needed for reservoir development and entrapment of petroleum from the Geneva Dolomite.

            Draping of younger, Middle Devonian strata over Silurian reefs has resulted in approximately 100 feet of structural closure on the Geneva carbonates at Sandoval and Raccoon Lake fields. Miletus Field shows 60 feet of structural closure, possibly reef related. St. James Field is an example of a Geneva reservoir located over a structural fold with no apparent reef influence. Regional mapping shows that thinning of the Middle Devonian carbonate interval overlying the Geneva Dolomite reservoirs is common.

            Examination of Geneva rock in Indiana quarries and core from central Illinois petroleum reservoirs shows similar characteristics. The dark brown, sucrosic, Geneva Dolomite with well developed moldic porosity is strikingly similar in both the quarries and the core. Dolomitization and porosity development is widespread and appears to be facies related. The greatest porosity development is correlated with facies that were originally composed of bioclastic packstones and wackestones.

            To account for the widespread and uniform dolomitic character of the Geneva, we suggest a regional mixing-zone model of dolomitization. The model would require that the Geneva carbonates were subaerially exposed, subjecting the sediments to an influx of meteoric waters. The influx of these waters through the Geneva carbonates would establish a mechanism for dolomitization, the associated enhanced porosity and permeability and the solution and brecciation observed in the Geneva. Widespread subaerial exposure of the Geneva carbonates prior to deposition of the overlying sediment would establish the top of the Geneva as a sequence or parasequence boundary.

Facies and Conodont Content of a Condensed Interval: Mississippian (Chesterian) Bangor Limestone, Central Tennessee and North Alabama

STAPOR, FRANK W., JR., Dept. of Earth Sciences, Box 5062, Tenn. Tech. Univ., Cookeville, TN 38505; and DANIEL L. NORTH, Illinois State Geological Survey, 615 E. Peabody Dr., Champaign, IL 61820

            A distinctive argillaceous wacke-packstone unit is present within the repetitious sequence of essentially identical sub-tidal to supratidal facies units that comprise the m- to 10's of m-thick Bangor Limestone parasequences. In northcentral Tennessee this unit is a 2.5 m-thick, very thickly bedded to “massive”, burrowed to bioturbated, argillaceous wacke- and packstone. In southcentral Tennessee and northcentral Alabama it thickens to 9 meters and consists of decimeter-thick, argillaceous, silty, wacke- and packstone interbedded with centimeter-thick, calcareous, silty, claystone. At its southernmost occurrence in northcentral Alabama, it is a 3.5 m-thick sequence of interbedded, decimeter-thick, skeletal grainstone tempestites and extremely fossiliferous, silty shale. It has a higher conodont content, 33-125 elements/kg, than that of the repetitious facies units, <15 elements/kg. This content decreases from 125 elements/kg at the southernmost occurrence to 33 elements/kg at the northernmost.

            The facies and conodont content of this unique Bangor unit strongly suggest that it is indeed a condensed interval with the amount of stratigraphic condensation increasing to the south. Because this unit is not present in northernmost Tennessee, this transgression terminated in southern Kentucky. It can be used to divide the Bangor Limestone into a lower transgressive systems tract, that thins to the north, and an upper highstand. The high-stand Bangor has a progradational facies relationship with the Pennington Shale of central Tennessee and northeast Alabama.

The English Graben: a Seismic Study of the Relationship Between a Proterozoic Rift Segment and Subsequent Paleozoic Structure and Strata

STARK, T. JOSHUA, Tulsa, OK; STEPHEN H. ROWLEY, Emet Consulting, Plano, TX; CARL K. STEFFENSEN, Vastar Resources Inc., Houston, TX; JAMES A. DRAHOVZAL, Kentucky Geological Survey, Lexington, KY; and LOUIS E. SCHULTZ, Williams Gas Pipelines Texas Gas, Owensboro, KY; GLENN W. BEAR, Exxon, Houston, TX; STEVE BERGMAN, ARCO EPT, Plano, TX

            The English Graben is interpreted as a polyphase rift, underlain by Mesoproterozoic strata and filled with Neoproterozoic / Cambrian sediments, forming a portion of the East Continent Rift Complex in areas of Kentucky and Indiana. The western margin of the graben is presently expressed by shallow faults offsetting Paleozoic strata, interpreted to be related to the remobilization of deep-seated Proterozoic faults. The eastern margin is defined by the Louisville Accommodation Structure (LAS), a high-relief fault-bounded basement feature expressed in pre-Mount Simon strata by a series of shallow fault systems. The northern extension of this bounding feature is the Mt. Carmel Accommodation Structure (MCAS). Seismic data is interpreted to exhibit flanking pre-Mount Simon basins and complex extensional faulting associated with the MCAS.

            Evidence from potential field data indicates deformation of the graben, with several kilometers of transcurrent displacement apparent along the margins of the rift segment. Earthquake epicenters recorded in the area may be localized along these transcurrent systems, responding to current east-west horizontal maximum principle compressive stress. Hydrocarbon fields occur along the margins of the graben, and appear to be associated with structural remobilization of bounding fault systems.

            Both proprietary and published seismic sections demonstrate the existence of a complex structural depocenter with multiple stages of deformation and a depth to crystalline basement exceeding 6100 m. Four borehole penetrations of the pre-Mount Simon sequence in the area of the graben suggest that the depocenter is filled with Neoproterozoic and/or Cambrian strata and underlain by the Mesoproterozoic Middle Run Formation/Centralia Sequence. Variations in stratigraphic thickness and lithology are noted in association with the graben margins, and it is suggested that the epeirogenic remobilization of the rift margins has controlled the Paleozoic structural and stratigraphic development of the area.

The Historic Trenton Broad Ripple Fields: A Quaint Story or a Unique Reservoir Study?

STRUNK, KEVIN LEE, Wabash Resources & Consulting, Indianapolis

            Detailed accounts of the discovery, development and demise of the Broad Ripple Field are contained within the Annual Reports of the State Geologist from 1896 to 1908, the 1922 Indiana Handbook, and records of the Ohio (Standard) Oil Company, with 1939-40 newspaper accounts and completion reports available for the Broad Ripple South Field. Broad Ripple is a scenic old farming community cum trendy entertainment and residential district in north-central Indianapolis. Development patterns near the White River give some field areas a semi-rural character, with many drilling locations and one plugged well casing identifiable. The Broad Ripple Field was discovered in 1888 when local farmers began drilling domestic-use gas wells. Oil shows led to a local "boom" from 1896-1906 (and 1918-19?) culminating in the completion of at least 68 oil and gas wells (1500 MCF IP reported) in a 2200+ acre area. Gas was piped downtown and into Broad Ripple. Initial oil production rates up to 150 BOD attracted the interest of Standard Oil who drilled a 300 BOD well, and many smaller wells. Total field production was at least 235,000 BO with a peak of 102,087 BO in 1898. Many of the wells or leases have gas-oil-water contacts, production decline curve and other reservoir data, and portions of the field interior have closely spaced structural data. Residential subdivision platting and declining production led to all wells being plugged by 1908, apparently without the field having been fully delineated. A dry step out drilled in 1940 was the finale. The smaller South Field may have been wildcatted as early as 1918. Five wells were drilled 1939-40, and 1950, apparently being non-commercial. Structure mapping shows that the fields are related to a southwest plunging anticlinal structure and regional faulting, with local closure, dolomite porosity, and fracturing on the extreme southwest flank of the giant Trenton Field. An aero-magnetic low overlies the productive area, along with a bedrock high.

Aquifer Heterogeneity, Anthropogenic Effects and a RCRA Facility Investigation Case Study

SVITANA, KEVIN, P.G., URS Greiner Woodward Clyde, Columbus, OH 43215

            The importance of understanding anthropogenic effects and aquifer heterogeneity when assessing plume migration is discussed in this paper. The discussions are based on a RCRA Facility Investigation (RFI) completed at a 13-acre solvent recycling center in Central Ohio. The RFI was in response to a waste solvent release that occurred over a decade ago.

            The data collected during the RFI indicated a shallow unconfined aquifer with a potentiometric surface sloping towards the northwest. Water sample analyses from monitoring wells indicated the highest concentration of solvents were northeast of the release point; no solvents were down gradient of the release. To understand why contaminants were not migrating in the direction of groundwater flow, additional assessment and investigation of site development history was completed.

            Slug and pumping test data suggested that near surface sand layers were not laterally continuous. Slug tests indicated hydraulic conductivity’s ranging from 1x10^-3 to 1x10^-6 centimeters/second, indicating heterogeneity of the subsurface soils.

            The construction contractor who built the facility revealed that undocumented dewatering trenches were dug between foundations, tank cavities and storm sewers. Subsequent investigations conducted in the vicinity of the dewatering trenches revealed soil and groundwater had the highest concentrations of the released solvents. Hydraulic testing indicated that manmade conduits were the primary pathways of migration.

            To prevent off site discharge of solvents, corrective measures to control ground water flow were developed that include a cut off wall and sumps, recovery wells, and a dual phase recovery system. Evaluation of the on-going remediation will be presented.

The State of Indiana’s Policy on Natural Attenuation of Petroleum Hydrocarbons as a Site Remediation Alternative

THOMPSON, ROD; JEFF MOODY; and MICHAEL ANDERSON, Indiana Department of Environmental Management, Indianapolis, IN

            The proposed Indiana Department of Environmental Management’s policy on natural attenuation of petroleum hydrocarbons will be discussed. The policy is included in the IDEM Risk Integrated System of Closure (RISC) document, which outlines the approach for site remediation and the use of natural attenuation as one alternative. Examples of the new policy implementation will be provided in the presentation.

First Results of Remediation with BIOx

TROY, PAUL, BILL LUNDY, KURT BYANSKI, VENKAT REO, ATC Associates, Inc., Indianapolis

            Remediation of soil and groundwater contaminated with chlorinated solvents at a former underground storage tank site is attempted using BIOx, a jettable slurry of calcium hydroxide and hydrogen peroxide. A 5-10% BIOx slurry is jetted into the subsurface using a high-pressure wand which advances its boring by liquefication of the soil in front of it. The speed and ease of jetting allowed borings to be placed approximately 1.5 feet apart, to a depth of approximately 15 feet. Comparison of groundwater sample results collected before and 4 weeks after treatment indicate that regulated dissolved chlorinated compound concentrations have declined approximately 50%. The mechanism of affect is expected to continue to reduce concentrations for several weeks.

Coalbed Methane Potential, Core and Pilot Program, Illinois Basin

WHEAT, RUSTY, W., MCMI Consulting Geologist, Brownsburg, IN

            Mid-Continent Methane Incorporated (MCMI) has recently completed an extensive assessment of the potential coalbed methane resources across a 40,000-acre lease located in Saline and Williamson Counties of Illinois. The study area is located along the Cottage Grove Fault System.

            The 1,000 feet of Pennsylvanian stratigraphy contain an average of 35 feet of total coal in an average of 7 different coal seams. The gas content of the coal was measured from six (6) complete cores (over 100 coal samples) ranging in depths from 300 to 1,000 feet. A total of ten (10) isotherms on individual seams were performed. Diffusivity tests were conducted and measured in the laboratory using xenon gas and core re-equilibration. Cleat density and spacing were measured in the laboratory using CT imaging. Bureau of Mines lost gas estimates were compared to core re-equilibration measurements. Over 20 gas quality samples were obtained from coal canister and production tests.

            Twelve pilot wells have been completed. Production tests include single coal seam tests, slug tests and interference tests. Pilot tests were used to forecast well spacing. Water quality measurements indicate potential for discharge to surface waters.

            The results of the core program indicate significant volumes of gas in place. The results of the pilot program indicate several geological factors may have control over field orientation and production rates. The pilot program was successful in determining the geological factors that will ultimately place the Illinois Basin into coalbed methane commercial production.

Basement Control on Structures in the Deforming Alleghanian Wedge, Southern-Central Appalachians

WHISNER, J. B.¹, R. D. HATCHER, Jr.^1,2, P. D. LEMISZKI³, C. MONTES^{1 1}Department of Geological Sciences, University of Tennessee, Knoxville, TN, ²Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, ³Tennessee Division of Geology, 2700 Middlebrook Pike, Knoxville, TN

            Important constraints on the growth of a fold-thrust belt (FTB) include the shape and depth of basement beneath the deforming sedimentary wedge. Our first step in developing a three-dimensional model of the southern Appalachian FTB involved compiling all available industry, academic, and U.S./state geological survey well and seismic reflection data on basement elevation. We have combined our compilation of the basement surface in the southern Appalachians with Shumaker’s 1996 map of the central Appalachians to develop a contour map of the basement surface for the Appalachian orogen from Alabama to New York. In the Tennessee embayment (GA to VA), the basement surface dips gently to the SE and contains several NE-striking down to the southeast normal faults related to Late Proterozoic-earliest Cambrian rifting events along the Laurentian margin. These basement structures likely influence structures in the FTB. Down-dropped basement blocks may have permitted deposition of a thicker stratigraphic sequence. For instance, major thickness changes in the Cambrian rifted-margin deposits of the Rome Fm. and Conasauga Group may be the stratigraphic expression of basement features. Normal faults in the basement may also localize detachment folds or ramps, limit thrust displacement, and influence the spacing of thrust faults in the FTB. Areas in which basement appears to affect FTB structure include the Valley and Ridge province in Alabama and Georgia and the Pine Mountain thrust sheet. In addition, fault spacing in the Appalachians increases towards the foreland, whereas in the Canadian Cordillera, fault spacing increases towards the hinterland.

Sub-Ravencliff Unconformity and Associated Ravencliff Incised Valley System, Upper Mississippian Mauch Chunk Group, West Virginia

YANG, CHAOQING, Berry Energy Consultants & Mgr's, Inc., Clarksburg, WV

            Detailed subsurface well-log correlation and mapping revealed a regional unconformity (the sub-Ravencliff) and associated incised valleys at the base of the Ravencliff Formation of the Upper Mississippian Mauch Chunk Group in central and southern West Virginia. The sub-Ravencliff unconformity, a type-1 sequence boundary, forms the lower bounding surface of the Ravencliff–Pocahontas sequence that is bounded above by the sub-New River unconformity.

            Although tectonic control is evident as is indicated by the southeasterly tilted sub-Ravencliff strata, the extensive regional truncation and channel incision at the sub-Ravencliff time may also have been influenced by a eustatic sea-level fall. In response to the fall of relative sea level, the shoreline retreated southward over 100 miles from the Avis to Ravencliff time. Consequently, incised valleys carved into the exposed shelf as deep as 160 feet with width ranging from 10 to 30 miles.

            The incised valleys were filled during the subsequent rise in relative sea level with fluvial quartzose sands (the Ravencliff sandstone), derived primarily from the northern cratonic source. As relative sea-level rise continued, the incised valleys were turned into estuaries, filled with mud-dominated deposits of tidally-influenced environments. Maximum marine flooding represented by the highly radioactive Pride Shale of the Bluestone Formation was followed by the northwestward progradation of the Bluestone-Pocahontas clastic wedge. Regional uplift and coeval eustatic sea-level drop during latest Mississippian and Early Pennsylvanian emerged most of the central Appalachians and ended the Ravencliff-Pocahontas sequence.

Three-Dimensional Modeling of the Mississippian Ste. Genevieve Limestone Shoal Complex at Owensboro North Consolidated Field, Gibson County, Indiana

ZUPPANN, CHARLES W. and MICHAEL O'NEAL, Indiana Geological Survey, Bloomington, IN

            Intervals of porous and permeable limestone that occur within less porous carbonate strata commonly have been used to infer the depositional geometry of oolite “bars” in the Ste. Genevieve Limestone (Mississippian) in the Illinois Basin subsurface. Understanding the distribution and geometry of these “porosity bodies” is economically significant because they represent some of the more productive hydrocarbon reservoirs in the basin. However, Ste. Genevieve porosity bodies are notoriously difficult to correlate because typically they exhibit thin, lens-shaped geometries that are locally distributed and develop in multiple stratigraphic positions. Furthermore, the geophysical log signatures of the porous zones become indistinct on the margins of the porosity bodies.

            More than 400 wells were used in an interactive computer model developed at the Indiana Geological Survey to visualize the three-dimensional geometries of the “shoal” facies at Owensville North Consolidated Field. Our initial correlation step was to group all apparent shoal-related facies together (porous and nonporous grainstones and packstones), and to model the geometry of this composite group. The porous intervals were then correlated and interpreted relative to their position within in the shoal body. The Ste. Genevieve does not appear to represent a collection of isolated bars, but rather a large shoal complex on which sites of oolite deposition shifted, expanded, and contracted over time. Oolitic porosity bodies only formed in local parts of the bigger shoal, especially where the shoal is relatively thick. Porosity may have developed in these areas as a result of vadose diagenesis that developed as the shoal built up sufficiently to be influenced by meteoric water.