TITLE PAGE Creating a Geologic Play Book for Trenton-Black River Appalachian Basin Exploration Semi-Annual Report Reporting Period Start Date: April 1, 2005 Reporting Period End Date: September 30, 2005 Principal Authors: Douglas G. Patchen, Taury Smith, Ron Riley, Mark Baranoski, David Harris, John Hickman, John Bocan and Michael Hohn October 2005 DOE Award Number: DE-FC26-03NT41856 West Virginia University Research Corporation P.O. Box 6845, Morgantown, WV 26506-6845 University of Kentucky Research Foundation 109 Kinkead Hall, Lexington, KY 40506-0057 New York State Museum Institute Room 3140 CEC, Albany, NY 12230 Ohio Division of Geological Survey 4383 Fountain Square, Columbus, OH 43224 Pennsylvania Geological & Topographic Survey 400 Waterfront Drive, Pittsburgh, PA 15222-4745 West Virginia Geological & Economic Survey 1 Mont Chateau Road, Morgantown, WV 26508-8079 DISCLAIMER “This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.” ii ABSTRACT Preliminary isopach and facies maps, combined with a literature review, were used to develop a sequence of basin geometry, architecture and facies development during Cambrian and Ordovician time. The main architectural features – basins, sub- basins and platforms – were identified and mapped as their positions shifted with time. This is significant because a better understanding of the control of basin geometry and architecture on the distribution of key facies and on subsequent reservoir development in Ordovician carbonates within the Trenton and Black River is essential for future exploration planning. Good exploration potential is thought to exist along the entire platform margin, where clean grainstones were deposited in skeletal shoals from Indiana thorough Ohio and Ontario into Pennsylvania. The best reservoir facies for the development of hydrothermal dolomites appears to be these clean carbonates. This conclusion is supported by observations taken in existing fields in Indiana, Ontario, Ohio and New York. In contrast, Trenton-Black River production in Kentucky and West Virginia has been from fractured, but non-dolomitized, limestone reservoirs. Facies maps indicate that these limestones were deposited under conditions that led to a higher argillaceous content than the cleaner limestones deposited in higher-energy environments along platform margins. However, even in the broad area of argillaceous limestones, clean limestone buildups have been observed in eastern outcrops and, if present and dolomitized in the subsurface, may provide additional exploration targets. Structure and isopach maps developed as part of the structural and seismic study supported the basin architecture and geometry conclusions, and from them some structural control on the location of architectural features may be inferred. This portion of the study eventually will lead to a determination of the timing relative to fracturing, dolomitization and hydrocarbon charging of reservoirs in the Trenton and Black River carbonates. The focus of this effort will shift in the next few months from regional to more detailed structural analyses. This new effort will include topics such as the determination of the source of the hot, dolomitizing fluids that created hydrothermal dolomite reservoirs in the Black River, and the probable migration paths of these fluids. Faults of suitable age, orientation and location to be relevant for hydrothermal dolomite creation in the Trenton-Black River play will be isolated and mapped, and potential fairways delineated. A detailed study of hydrothermal alteration of carbonate reservoirs was completed and is discussed at length in this report. New ideas that were developed from this research were combined with a literature review and existing concepts to develop a model for the development of hydrothermal dolomite reservoirs in the study area. Fault- related hydrothermal alteration is a key component of this model. Hydrothermal alteration produces a spectrum of features in reservoirs, ranging from leached limestone and microporosity to matrix dolomite, saddle dolomite-lined breccias, zebra fabrics and fractures. Mineralization probably occurred during the pressure drop associated with the rise of fluids up the fault system, and is due to the mixing of hydrothermal fluids with cooler, in situ fluids. Once they began to cool themselves, the hydrothermal fluids, which had a lower pH and higher salinity than formation fluids, were capable of leaching the iii host limestones. Microporosity is common in leached limestones, and it is likely that it was formed, in some cases, during hydrothermal alteration. Dolomite leaching occurs near the end of the paragenetic sequence, and may significantly enhance porosity. However, leaching of dolomite typically is followed by the precipitation of calcite or anhydrite, which reduces porosity. A final conclusion is that hydrothermal alteration may be more common than previously thought, and some features previously attributed to other processes may be in fact be hydrothermal in origin. Production data are being collected from all project partners. These data will be used to predict ultimate production from existing fields for which a complete production history is known, and for remaining reserves in fields for which the complete production history is unavailable. A plan to estimate the gas resource in the entire play area is being developed. Enhancement of the project database, GIS and website was emphasized during the report period. The website, like the database, remains a work in progress, and can only grow when the database grows. Recent improvements to the website included how we serve well log files. An effort is being made to add all logs - approximately 1800 - that have been scanned in Tiff format, and another 500 logs that have been converted to vector (LAS) format, to the database and website. Tables for production data, log data, core data and cross sections, all linked to the well header information, were created. iv TABLE OF CONTENTS Page Title page i Disclaimer ii Abstract iii Table of Contents v Executive Summary 1 Results and Discussion 3 Regional Stratigraphy of the Trenton-Black River Interval 3 Geologic Structure and Seismic Analysis 41 Hydrothermal Alteration of Carbonate Reservoirs 45 Analysis of Production Data 84 Database, GIS and Website Management 85 Conclusions 90 References 91 Page Title Page i Disclaimer ii Abstract iii Table of Contents v Executive Summary 1 Results and Discussion 3 Conclusions References 99 List of Acronyms and Abbreviations Appendix v EXECUTIVE SUMMARY The Trenton-Black River Appalachian Basin Research Consortium is rapidly approaching their goal of producing a geologic play book for the Trenton-Black River gas play. The final product will include a resource assessment model of Trenton-Black River reservoirs; possible fairways within which to concentrate further studies and seismic programs; and a model for the origin of Trenton-Black River hydrothermal dolomite reservoirs. Fairways are being identified, based on the structural, stratigraphic, petrographic, geochemical and production studies, and a final model for the origin of hydrothermal dolomites in the Trenton-Black River interval is nearly complete. The petrographic study was completed during the reporting period. This effort of the Appalachian Oil and Natural Gas Research Consortium (AONGRC) is being conducted by a Trenton-Black River Research Team consisting of recognized experts employed by the state geological surveys in Kentucky, Ohio, Pennsylvania and West Virginia, and the New York State Museum Institute. The AONGRC organized this team and recruited seventeen gas production and exploration companies to form an industry-government-academic partnership, the “Trenton-Black River Appalachian Basin Exploration Consortium,” that agreed to co-fund and conduct the research effort. During this reporting period, geologists on the Stratigraphy Task Team finalized the regional cross section network, completed the interpretation of geophysical logs for regional mapping, generated preliminary regional isopach maps for selected intervals, and constructed generalized facies maps for the Black River and Trenton/Point Pleasant intervals. These geophysical log data were integrated with core and sample descriptions and published outcrop and subsurface studies of the Middle and Upper Ordovician. A network of 19 regional cross sections was generated to illustrate the regional stratigraphy of this interval. All logs for the 222 wells used in these cross sections were converted to LAS (Log ASCII Standard) format. Approximately 1800 geophysical logs that were used in constructing the various isopach and facies maps were scanned (Tiff format) and 500 of these also were converted to vector (LAS) format. These maps were used to develop a better understanding of the basin architecture and facies distribution during Middle and Upper Ordovician time. Core descriptions and detailed log analysis defined clean carbonate intervals within this basin architecture and facies distribution pattern that have good potential for hydrothermal dolomite (HTD) reservoir development. The facies distribution patterns also may explain why HTD reservoirs were not developed in other areas. Data acquisition for the Seismic and Structural Geology task has been completed. Digitized geophysical well logs for 402 wells and stratigraphic tops from 1797 wells were used for seismic correlation and structural analysis. All raw data have been loaded into software packages: digital seismic data (SEGY files) into Seismic-Micro Technology’s Kingdom Suite software, and raster images (Tiff files) into the PetraSeis module of Geoplus Petra software; and digital geophysical log data into Petra and Kingdom Suite software. Sonic logs for 114 wells were used to create synthetic seismograms and velocity models, which were then used to transform known well top depths in feet subsea to depths in time for seismic correlations. In addition, fault trend mapping is nearing completion. Once complete, this mapping effort will 1 identify structural fairways that may be more prone to the development of fault-related hydrothermal dolomites. Seismic and structural data, combined with stratigraphic and facies data, and petrographic and geochemical analyses, were used to develop the model of HTD reservoir development. This report contains an extensive discussion of the hydrothermal alteration of carbonate reservoirs based on current research results and a literature search of previous studies that are applicable to this effort. First-order controls on hydrothermal alteration include the composition, thickness, porosity and permeability of the limestone host rock; the pressure, temperature and chemistry of the hydrothermal fluid; the effectiveness of an overlying sealing unit; the distance between the basement and basal sandstone aquifer up to the host limestone; and the type and timing of faulting. Structural settings where hydrothermally-altered carbonates commonly are found include margin-bounding faults, newly-rifted basement and active normal faults, fault intersections, and around wrench faults that are activated during mountain building events. Fault-related hydrothermal alteration occurs when high-pressure, high-temperature fluids flow up active faults and then move laterally into permeable formations when upward movement is restricted by an overlying seal, such as an impermeable shale, argillaceous limestone or evaporate unit. Alteration of the original limestone host rock proceeds due to the episodic influx of fluid up a fault, the mixing of the deeper fluids with fluid in the host rock, and subsequent equilibration with formation conditions. These hydrothermal fluids not only create dolomite, but as they cool they also have the capacity to leach limestone and, in some cases, dolomite that had been created when the fluids were warmer. Microporosity is common in these leached limestones, and leached dolomites also may significantly enhance porosity. Production data are still being collected from the various state agencies in the play area. As up-to-date-as-possible data are necessary to achieve the maximum results, so this data collection effort will continue for the next several months. These data will be used to predict the estimate ultimate recovery of existing Trenton-Black River fields for which a complete production history can be collected; remaining production from fields for which the early production history is unknown; and for estimating gas resources in the entire play area. A plan is being prepared to estimate gas resources. The decision has been made to work with outside industry and government experts to accomplish this task. The project website continues to be a work in progress. In its current configuration, growth is limited by the amount of information in the database. Efforts were made to increase the amount of project data that are now considered to be final and, therefore, appropriate to be included in the database and on the website. As an example, progress was made on the number of LAS and Tiff files for well logs that were added to the database and website. During the recent meeting of research team members with company consortium members, the industry representatives requested access to all header information and expressed satisfaction with the format and contents of the database and website. This technical report does not contain a section on results of the petrology task. However, a separate topical report that summarizes the final results of this task will be submitted as a companion to this semi-annual technical report. 2 RESULTS AND DISCUSSION Regional Stratigraphy of the Trenton-Black River Interval The primary focus of the stratigraphy task is to define Trenton, Black River, Utica and equivalent lithostratigraphic units within a regional framework; model the depositional environment and basin architecture; and integrate these results with the results from other project tasks to delineate potential areas of exploration interest. The stratigraphic framework will establish regionally-consistent formation/interval boundaries and nomenclature, which will be used in structure, isopach and facies mapping. A regionally-consistent stratigraphic framework also will provide a better understanding of the complexly interwoven geologic parameters controlling Trenton-Black River reservoirs. Once a consistent framework is developed one can map and isolate lateral facies changes that may have been tectonically influenced during deposition and possibly later during reservoir development. The ultimate goal of the stratigraphy task is to develop the regional stratigraphic framework, which then will be integrated with results from other tasks to develop a stratigraphic-structural-diagenetic model for the origin of Trenton- Black River reservoirs and delineation of potential areas of exploration interest. Methods During the past semiannual report period, geologists in the Stratigraphy Group finalized the regional stratigraphic cross section network, completed the interpretation of geophysical logs for regional mapping, generated preliminary regional isopach maps for selected intervals of the Cambrian-Ordovician section, and constructed preliminary, generalized facies maps for the Black River and Trenton/Point Pleasant intervals. Geophysical log data were integrated with core and sample descriptions and published work on Middle and Upper Ordovician outcrop and subsurface studies. Core data are located primarily in the western portion of the Appalachian basin in western Ohio and central Kentucky and are sparse in the deeper portion of the basin in New York, West Virginia and Pennsylvania. Geographix software was used for constructing the cross sections and maps. A network of 19 cross sections has been generated across the Appalachian basin to illustrate the regional stratigraphy of the Middle and Upper Ordovician succession of strata (Figure 1). All logs for the 222 wells used in constructing these cross sections have been converted to LAS (Log ASCII Standard) format for construction of the final cross sections. Throughout the basin, approximately 1,800 geophysical logs for unique wells containing the Trenton-Black River interval have been scanned (Tiff format) and approximately 500 well logs have been converted to vector (LAS) format. A depositional-strike direction of approximately northeast-southwest for the Trenton interval was established using a preliminary isopach map and other published maps. It generally is assumed that parallel isopach contour lines showing thick to thin areas define a regional deposition strike direction. Seven cross section lines were oriented parallel (strike) and 12 cross section lines were oriented perpendicular (dip) to the depositional strike. Wells were prioritized for use in cross sections that contained continuous Trenton/Black River cores or Precambrian penetrations. Formation picks on logs used in these cross sections were correlated to described 3 cores and digital photographs to refine the lithostratigraphic correlations. Dolomitized zones from geophysical logs and cores also are being noted and mapped to help delineate potential areas of fault trends, the assumption being that the dolomites are fault related. The Stratigraphy Group completed the interpretation of geophysical logs and picked tops for all wells that will be used in the regional isopach maps. Units that were interpreted on geophysical logs (using Ohio and Kentucky nomenclature) include the top of the Knox Dolomite, Wells Creek Formation, “Gull River,” Black River Limestone, Lexington Limestone (with its Curdsville Member, Logana Member and Lexington Undifferentiated Member), Trenton Limestone, Point Pleasant Formation, Utica Shale, Kope Formation, and top of the Ordovician. Equivalent units and nomenclature for the entire Appalachian basin can be seen in the regional stratigraphic correlation chart (Figure 2). As with the wells used in the cross sections, geophysical log tops were correlated to cores and sample descriptions to better refine the stratigraphic interpretation. Preliminary thickness maps of the Precambrian to base of Knox, base of Knox to top of Knox, Knox to Black River, Black River to Trenton, Trenton to Kope, and Kope to top of Ordovician intervals were generated based on formation tops interpreted from approximately 1000 well logs, cores, and sample descriptions. Digital locations of Trenton–Black River oil and gas fields were obtained from Appalachian, Illinois and Michigan Basin states (including Ontario, Canada) and a Trenton-Black River oil and gas fields map was generated to assist in relating stratigraphy to producing trends (Figure 3). Preliminary facies maps illustrating late Black River time and late Trenton-Point Pleasant time were constructed to develop a better understanding of the paleogeography and facies distribution of these units. Preliminary maps illustrating the regional distribution of the Logana Member of the Lexington Limestone, the Point Pleasant Formation and the Utica Shale also were constructed. These maps were all generated using the regional cross sections, core and sample descriptions, and published references. Regional facies maps will be refined for the final report as data from all states are further integrated into the regional stratigraphic picture. Stratigraphic Nomenclature Again, the focus for this study is to develop a regionally-consistent stratigraphic framework for the Trenton/Black River-Utica interval and coeval units. Numerous stratigraphic names have been applied to the Ordovician succession of rocks across the Appalachian basin. To simplify the use of stratigraphic nomenclature in this report, Ohio and Kentucky nomenclature will be used in the stratigraphy discussion. Stratigraphic equivalents of these units across the basin can be seen in the regional stratigraphic correlation chart (Figure 2). A correlation chart based on the formal nomenclature of each state geological survey was subdivided into the northwestern basin and arches, the Rome Trough, and the eastern basin. The Cambrian and Ordovician units that were mapped are discussed in ascending stratigraphic order. Preliminary Summary of Central Appalachian Basin Geometry and Architecture During Ordovician Trenton Time 4 Figure 1. Map showing location of cross section lines (red lines) used in study and a facies map of late Trenton/Point Pleasant time. Cross sections presented within this report are highlighted and labeled. 5