Browsing by Author "Bebout, Don G."

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Characterization of the Grayburg Reservoir of the Mobil University unit 15/16 in Dune Field, Crane County, Texas
(1985) Bebout, Don G.; Leary, D. A.; Lucia, F. Jerry
A project was initiated by the Bureau of Economic Geology in 1981 to investigate the distribution and nature of oil production in Texas. Approximately 500 reservoirs having a cumulative production of more than 10 million barrels of oil each were included in this study; these reservoirs have produced more than 71 percent of the total Texas production. These larger reservoirs were grouped into 47 plays based on the original depositional setting of the rocks and source and on reservoir and trap characteristics. Twenty-seven of these plays located in the Paleozoic basins of North and West Texas account for 73 percent of the total in-place oil in the state. Most of the Paleozoic production is from dolomite reservoirs. Results of this initial reservoir characterization project by the Bureau are summarized in the "Atlas of Major Texas Oil Reservoirs" (Galloway et al., 1983). Reservoirs producing from the San Andres/Grayburg Formations were selected for study because of their high cumulative production and low recovery efficiencies (30 percent average). For example, in Texas, 51 percent (80 billion barrels) of the original oil in place and 43 percent (46 billion barrels) of the cumulative production are from the Permian Basin (Figs. 1 and 2). Within the Permian Basin, 83 percent (16.6 billion barrels) of the cumulative production is from carbonates (Fig. 3), and 46 percent (7.7 billion barrels) of this is from San Andres/Grayburg reservoirs (Fig. 4). Therefore, San Andres/Grayburg reservoirs are major contributors to Texas oil production (17 percent of the total cumulative production of Texas) (Fig. 5). Better geological definition of reservoirs incorporated into engineering models and studies should lead to more efficient development of secondary and tertiary recovery methods.
Effects of Stratal Architecture and Diagenesis on Reservoir Development in the Grayburg Formation: South Cowden Field, Ector County, Texas
(1995) Ruppel, Stephen C.; Bebout, Don G.
The Grayburg Formation in the South Cowden field of eastern Ector County displays an internal stratal architecture that typifies Grayburg shallow-water platform successions throughout the Permian Basin. Study of core and wireline logs in South Cowden field documents three orders of cyclicity in the Grayburg. The entire Grayburg constitutes a single long-duration accommodation cycle that commenced with a major sea-level rise and flooding of the preexisting San Andres platform and ended with a major basinward shift in facies associated with sea-level fall prior to deposition of Queen Formation tidal-flat successions. Four high-frequency sequences are recognized within the Grayburg that correspond to higher frequency sea-level rise events. The basal Grayburg sequence consists of backstepping, low-energy, mud-dominated cycles and is not a contributor to production in the field. Grayburg sequence 2 documents extensive flooding of the San Andres platform by outer ramp fusulinid wackestone-packstone facies and subsequent aggradation of an extensive tidal-flat-capped, grain-dominated packstone-grainstone ramp crest succession. Renewed platform transgression in Grayburg sequence 3, demonstrated by even more extensive onlap of the platform by fusulinid facies, documents a maximum flooding event that is correlatable throughout the Grayburg in both outcrop and subsurface. This event forms the basis for correlation of the Grayburg succession throughout the Permian Basin. Grayburg sequence 4 reflects highstand reduction of platform-to-basin relief and a major basinward shift in facies tracts.
Geopressured Geothermal Fairway Evaluation and Test Well Site Location Frio Formation, Texas Gulf Coast
(1978) Bebout, Don G.; Gregory, A. R. (Alvin Ray), 1915-; Loucks, R. G.
Tertiary strata of the Texas Gulf Coast comprise a number of terrigenous depositional wedges, some of which thicken abruptly at their downdip ends as a result of contemporaneous movement of growth faults and underlying salt. The Frio Formation, one of these wedges, has been studied regionally by means of a grid of correlation cross sections aided by micropaleontological control. By means of these sections, the Frio was subdivided into six map units; maps of sandstone distribution within these units delineate principal elongate sandstone trends parallel to the Gulf Coast composed of deltaic, barrier-bar, and strandplain sandstones. These broad regional studies, followed by detailed local investigations, were pursued in order to delineate prospective areas for the production of geopressured geothermal energy. A prospective area must meet the following minimum requirements: reservoir volume of 3 cubic miles, minimum permeability of 20 millidarcys (md), and fluid temperatures of 300Â°F. Several geothermal fairways were identified as a result of this Frio study.
Geopressured Geothermal Prospects and Test Well Sites Wilcox Group and Frio Formation, Texas Gulf Coast
(1978) Bebout, Don G.; Gregory, A. R. (Alvin Ray), 1915-; Loucks, R. G.; Weise, Bonnie R.
The four geopressured geothermal prospects and test-well sites described in this report (fig. 1 and table 1) are believed to represent the most favorable locations for testing the resource along the Texas Gulf Coast. The regional and site-specific studies used in selecting the Frio prospects have been published by the Bureau of Economic Geology (Report of Investigations 91); the supporting studies for the Wilcox prospects will be published by mid-1979. Detailed stratigraphic and structural cross sections and net-sandstone and structure maps have been prepared for the fairways in which these prospects are located. It is anticipated that other prospects will be identified in these and other fairways during the course of further study and will be reported on later. It should be emphasized that these prospects and sites have been chosen on the basis of geology alone and that equally important environmental and legal (surface and mineral rights) aspects have not been considered. The total-resource values shown in the last two columns of Table 1 are very general estimates and are intended only to project an impression as to the magnitude of the resource in these local areas. A significant departure has been made in the manner in which the top of geopressure is picked in this report. In previous Bureau of Economic Geology reports, the top of geopressure is defined as the point at which the pressure gradient exceeds 0.7 psi/ft; the pressure gradient was determined primarily by plotting drilling-mud weights, a method recognized as highly tentative. For this report, the top of geopressure is picked at the depth at which the plot of the shale resistivity from the electrical log departs from the normal compaction curve. This method is believed to be considerably more reliable.
Geothermal resources, Frio Formation, middle Texas Gulf Coast
(University of Texas at Austin. Bureau of Economic Geology, 1975) Bebout, Don G.; Agagu, Olusegun Kokumo, 1948-; Dorfman, Myron
Knowledge of the regional sand distribution and its relationship to formation temperature and pressure is a preliminary step in evaluating the geothermal resources of the Frio Formation. At depths generally greater than 7,000 feet, the sands and shales of the Frio Formation are overpressured and undercompacted. The insulating effect of these overpressured and undercompacted sediments results in the accumulation of subsurface heat and, thus, high temperature water. The local variations of depth to top of geopressure are related to the distribution of sand and shale lithologies and to the location of growth faults. For more information concerning origin of geopressure or high temperatures, see Jones (1970) and Dorfman and Kehle (1974). Bruce (1973) discusses the nature of growth faults in detail. The resource in the geopressured zone consists of high-temperature water with relatively low salinity and with dis solved methane gas. The objectives of this study were to determine regional sand distribution of the Frio Formation, identify depositional environments, and delineate the geopressured zone and its relationship to sand/shale distribution, growth faults, and fluid temperatures in the Middle Texas Gulf Coast. This study is essentially an extension of that completed earlier for South Texas (Bebout, Dorfman, and Agagu, 1975); all correlation and mapping units are the same as those represented in the South Texas report. The Energy Research and Development Administration, through the Lawrence Livermore Laboratory, supported this study of the geothermal resources of the Frio Formation in Middle Texas Gulf Coast.
Geothermal resources, Frio Formation, south Texas
(University of Texas at Austin. Bureau of Economic Geology, 1975) Bebout, Don G.; Agagu, Olusegun Kokumo, 1948-; Dorfman, Myron
A preliminary study of the Frio sand distribution and formation temperatures and pressures was undertaken in order to define prospective areas in which a more detailed reservoir analysis is necessary prior to the selection of a site for a geothermal well. As the result of prospective oil wells that penetrated the Tertiary sediments, a geopressured zone containing fluids with high temperatures is known to occur along the Texas Gulf Coast. Few oil or gas wells produce from this area, and the regional sand distribution within these zones is not well known. Limited data, however, indicate that the pore spaces within the sands in the geopressured zone are filled with water which has high temperatures and relatively low dissolved-solids content, and which is saturated with methane. These waters are believed to be an important source of thermal energy and methane gas. For more information concerning the origin of the geopressured zone, see Dorfman and Kehle (1974) and Jones (1970). The first step in appraising the Gulf Coast geothermal resources entails a detailed geologic study of the main sand trends; the Frio and Wilcox Formations appear to be the best prospects. This report will deal largely with the Frio. The Wilcox Formation has been studied by Fisher and McGowen (1967). Other parts of the Tertiary which have been studied in detail are the Queen City Formation (Claiborne), which was reported on by Guevara and Garcia (1972), and the Jackson, reported on by Fisher and others (1970). The United States Atomic Energy Commission, through the Lawrence Livermore Laboratory, and the Center for Energy Studies, The University of Texas at Austin, supported this preliminary study of the geothermal resource of the Frio sands in South Texas. The South Texas area (from just north of Corpus Christi and south to the Rio Grande) was selected because the geopressured zone is known to occur here at shallow depths (Jones, 1970), and because of the abundance of oil well records for the area. The study includes a sand-facies analysis and an integration of the facies data with existing information relative to temperatures and pressures.
Geothermal resources, Frio Formation, upper Texas Gulf Coast
(University of Texas at Austin. Bureau of Economic Geology, 1976) Bebout, Don G.; Loucks, R. G.; Bosch, S. C.; Dorfman, Myron
The objective of this study is to identify major sand trends, which, along with subsurface temperatures and pressures, aid in evaluating the potential of producing geothermal energy from the Frio Formation, Upper Texas Gulf Coast. During the Tertiary, huge quantities of terrigenous sediments were deposited as gulfward-thickening sedimentary wedges along the Texas Gulf Coast. The sand and shale making up these wedges were transported across a broad fluvial plain and deposited in deltaic complexes or were reworked by marine processes into strandplains and barrier islands. Growth faults developed contemporaneously at the site of maximum deposition as a result of rapid loading of large quantities of delfaic and strandplain sands onto previously deposited prodelta and shelf muds. These growth faults allowed the accumulation of extremely thick sections of sand and also caused the isolation of many of these sand bodies from porous updip sands; pressured reservoirs developed after further loading and compaction (Bruce, 1973; Jones, 1975). This study is investigating geopressured geothermal reservoirs in this setting. Limited data obtained from deep wells drilled for oil and gas indicate that many of these large sand reservoirs are filled with water which has high temperature, is relatively low in total dissolved solids, and is saturated with methane gas. To be suitable for electric power generation, the reservoir should have a volume greater than 3 cubic miles (which is equivalent to 300 feet of sand distributed areally more than 50 square miles), permeability greater than 20 millidarcies, and subsurface temperatures higher than 300°F. This report reviews the results of the Bureau of Economic Geology regional study of the Frio Formation in the Upper Texas Gulf Coast. It is a continuation of two similar studies of the Frio in the Lower and Middle Texas Gulf Coast (Bebout, Dorfman, and Agagu, 1975; Bebout, Agagu, and Dorfman, 1975). The objective of these reports is to outline areas (fairways) which appear the most prospective for producing geothermal energy and which therefore deserve further, more detailed study.
Geothermal Resources, Wilcox Group, Texas Gulf Coast
(1978) Bebout, Don G.; Gregory, A. R. (Alvin Ray), 1915-; Gavenda, V. J.
Areas with the potential for containing geopressured geothermal fluids in economic quantities (geothermal fairways) occur in the Wilcox Group where the Gulfward-dipping sandstone/shale wedge thickens abruptly across a complex growth-fault system. This regional study of sandstone distribution in the Wilcox Group is part of a much broader investigation aimed at assessing the potential for the production of geothermal energy from the geopressured zone of the onshore Tertiary along the Texas Gulf Coast (Dorfman and Keuffel, 1975, 1976). The objective of the study is to identify areas where the Wilcox Group contains significant thicknesses of sandstone with subsurface fluid temperatures higher than 300Â°F. These favorable areas are termed geothermal fairways and are areas in which additional, more detailed work is recommended in the search for prospective geopressured geothermal test-well sites. Reports summarizing similar studies of regional assessment of the Frio Formation and a prospective test-well site have been published by the Bureau of Economic Geology (Bebout, Dorfman, and Agagu, 1975; Bebout, Agagu, and Dorfman, 1975; Bebout, Loucks, Bosch, and Dorfman, 1976; Bebout, Loucks, and Gregory, 1977). The geothermal potential of the Vicksburg Formation is summarized by Loucks (1978). Funding for the entire geopressured geothermal assessment program has been provided by the Division of Geothermal Energy, U.S. Department of Energy.
Handbook for logging carbonate rocks
(University of Texas at Austin. Bureau of Economic Geology, 1984) Bebout, Don G.
Internal Geometry of a Modern Carbonate Grainstone Shoal--an Analog for Hydrocarbon Reservoir Heterogeneity
(1994) Bebout, Don G.; Major, R. P.
We chose the ooid sand shoals of the Joulters Cays area of Great Bahama Bank for detailed sedimentological study to investigate the patterns of internal heterogeneity within a modern carbonate sand belt and to develop criteria for predicting the lateral extent of carbonate sand facies. Major facies identified from cores were (1) crossbedded, well-sorted ooids, (2) burrowed, poorly sorted ooids, and (3) poorly sorted ooids and mud containing Thalassia. Clast-rich zones and mud layers were also encountered. We propose that upon burial and compaction, the poorly sorted ooids and mud containing Thalassia will likely retain negligible porosity and permeability, whereas both the crossbedded, well-sorted ooids and burrowed poorly sorted ooids will likely maintain their high initial porosity and permeability. However, study of many ancient subsurface reservoirs indicates that the crossbedded, well-sorted ooids can undergo considerable cementation and have low resultant porosity and permeability. Thus, in many settings, the burrowed, poorly sorted ooids could retain the highest porosity and permeability. Additional cementation within the clast-rich zones, which occur in both the crossbedded, well-sorted ooids and burrowed, poorly sorted ooids, will result in thin, low-porosity barriers within a reservoir. Locally the surface configuration of the modern shoal complex at Joulters Cays was altered significantly by the passing of Hurricane Andrew in August 1992. Prominent wash over bars were planed off, and well-sorted ooids were deposited in low areas of the shoal where poorly sorted and mud-rich deposits of ooids had previously accumulated. The post-hurricane configuration of the shoal demonstrates how a single short-term depositional event contributed significantly to the internal heterogeneity of the shoal complex.
Memorandum of Understanding Between the United States Department of Energy and the State of Texas - Characterization of Oil and Gas Reservoir Heterogeneity
(1992) Tyler, N.; Barton, Mark D.; Bebout, Don G.
Ultimate recovery from Texas oil reservoirs at current technological and development levels is projected to be 36 percent of the oil in place. Thus, of the 165 billion barrels (Bbbl) of oil discovered statewide, 106 Bbbl will remain in existing reservoirs after recovery of proved reserves. This remaining resource is composed of residual oil (71 Bbbl) and mobile oil (35 Bbbl). The remaining mobile oil is conventionally recoverable but is prevented from migrating to the wellbore by intrareservoir seals or bounding surfaces. Reservoir architecture, the internal fabric or structure of reservoirs, governs paths of fluid migration during oil and gas production. Reservoir architecture is, in turn, the product of the depositional and diagenetic processes responsible for the origin of the reservoir. If an understanding of the origin of the reservoir is developed, reservoir architecture, and therefore the paths of fluid migration, become predictable. Thus, with a greater understanding of the fabric of the reservoir and its inherent control on the paths of fluid flow, we can more efficiently design and implement advanced recovery strategies.
Opportunities for Additional Recovery in University Lands Reservoirs -- Characterization of University Lands Reservoirs, Final Report
(1990) Tyler, N.; Bebout, Don G.; Garrett, C. M., Jr.; Guevara, Edgar H.; Hocott, Claude R.; Holtz, Mark H.; Hovorka, Susan D.; Kerans, C. (Charles), 1954-
In 1984, The University of Texas System funded a Bureau of Economic Geology project, "Characterization of University Lands Reservoirs," to assess in detail the potential for incremental recovery of oil from University Lands reservoirs by extended conventional methods. The objectives of the 5-year project were to quantify the volumes of unrecovered mobile oil remaining in reservoirs on University Lands, to determine whether the specific location of the unrecovered mobile oil could be delineated through integrated geoscience characterization of individual reservoirs, and to develop strategies to optimize recovery of this resource. Unrecovered mobile oil is mobile at reservoir conditions but is prevented from migrating to the wellbore by geologic complexities or heterogeneities. This final report describes results of the 5 years of research conducted on University Lands reservoirs. One hundred and one reservoirs, each of which has produced more than 1 million stock tank barrels (MMSTB) of oil, were included in a resource assessment and play analysis undertaken (1) to determine the volumes and distribution of all components of the University Lands resource base and (2) to select reservoirs for detailed analysis. These reservoirs collectively contained 7.25 billion barrels (BSTB) of oil at discovery, have produced 1.5 BSTB, and contain 200 MMSTB of reserves. Ultimate recovery at implemented technology is projected to be 24 percent of the original oil in place; thus, 5.5 BSTB of oil will remain after recovery of existing reserves. Unrecovered mobile oil (exclusive of reserves) amounts to 2.2 BSTB, and immobile, or residual, oil totals 3.3 BSTB.
Regional cross sections-- Central Basin Platform, West Texas
(University of Texas at Austin. Bureau of Economic Geology, 1985) Bebout, Don G.
In 1982, the Bureau of Economic Geology initiated a project to characterize the major oil fields of Texas. The project led to the compilation of an atlas summarizing the general geologic setting and production statistics of all fields that have produced more than 10 million barrels of oil (Galloway and others, 1983). During this compilation, the need arose for regional stratigraphic control for the various large fields on the Central Basin Platform, and these cross sections were constructed to fill this need. Well logs (mostly gamma ray/neutron, but also electrical and sonic} from wells spaced approxi- mately 5 mi apart are included on the 11 cross sections. Only the deepest wells are used, and most reach the Ellenburger Formation. Wherever possible the sections are directed through the major oil fields, those that have produced more than 10 million barrels of oil, and logs from those fields are included on the sections. The zone or zones of production are indicated on the well representing each field. Correlations of the entire Paleozoic section (fig. 1) were obtained from other published cross sections (West Texas Geological Society, 1962, 1964), cross sections and paleontological data from proprietary company files, compilations of oil-field studies (Herald, 1957; Stipp, 1960; West Texas Geological Society, 1966, 1969), and the records of the University Lands Office, Midland, and Railroad Commission of Texas, Austin. Where deep wells were not available a tectonic map of Texas (Ewing, in preparation) was used to aid in placing the tap of the Ellenburger Formation. Many disconformities are recognized in the Paleozoic section of the Central Basin Platform. However, only the regional! unconformity at the base of the Wolfcampian Series, where the rocks of entire geologic systems are missing, is indicated on the sections. Major faults are shown on the cross sections, and they are all indicated to be vertical because of lack of detailed data on the dip of the fault planes. The locations of the faults were obtained from the sources cited above or were recognized through identification of abrupt changes in elevation of markers from one weil to the next; the faults shown on the sections correspond to the major faults on the tectonic map compiled by Ewing (in preparation). These regional cross sections are intended to be used for preliminary correlation or to obtain an introduction to the geology of the Central Basin Platform area (fig. 2). For detailed information ona local area, reference shouid be made to the sources of field studies cited above.
Regional Tertiary cross sections, Texas Gulf Coast
(University of Texas at Austin. Bureau of Economic Geology, 1976) Bebout, Don G.; Luttrell, P. E.; Seo, J. H.
The Bureau of Economic Geology has been conducting regional studies of the Frio Formation along the Texas Gulf Coast to evaluate potential geothermal energy from deep, geopressured sandstone reservoirs (Bebout, Dorfman, and Agagu, 1975; Bebout, Agagu, and Dorfman, 1975). The procedures used in this evaluation were reviewed at the Second Geopressured Geothermal Energy Conference held at The University of Texas at Austin and sponsored by the United States Energy Research and Development Administration. The index map (fig. 1) and cross sections (figs. 2-7) included in this circular were prepared for that meeting and were included in the Proceedings (Bebout, 1976). Published regional cross sections (Corpus Christi Geological Society Study Group, 1954-55, 1964; Deussen and Owen, 1939; Houston Geological Society Study Group, 1954, 1972; and South Texas Geological Society, 1951), unpublished cross sections provided by several major oil companies, and extensive micropaleontological and electrical-log files at the Bureau of Economic Geology served as basic data. These sections are meant to show gross regional distribution of sand and shale facies both laterally and vertically throughout the entire Tertiary section along the Texas Gulf Coast. Closely spaced wells were used for detailed correlation, but for clarity many have been omitted for these cross sections (fig. 1 and table 1). Growth faults tend to obscure regional trends and have been omitted. The top of the geopressure zone is indicated by an arrow. At least eight sand-shale wedges are easily recognized on regional electrical-log cross sections (figs. 2-7). Hardin (1961) illustrated the major wedges as the Midway/Wilcox, Reklaw/Queen City, Weches/Sparta, Cook Mountain/Yegua, Jackson, Vicksburg, Frio, and Anahuac/Fleming. The Pliocene and Pleistocene comprise additional cycles but are undifferentiated in this study. These cycles reflect changes in the ancient shoreline resulting from variations in sediment supply, rate of subsidence, and position of sea level. In general, in the updip end of the wedge the main sand depocenter is in the lower part of the section and downdip it is progressively higher in the section; this is a progradational cycle. In order to emphasize these wedges, the boundary between the facies-related sand-shale couplet is defined by a dashed line on the cross sections. Time lines within the couplet are expected to cross the dashed line as the deltaic or barrier sands prograde basinward over the prodelta or shelf shales.
Relationship of porosity formation and preservation to sandstone consolidation history: Gulf coast lower Tertiary Frio formation
(University of Texas at Austin. Bureau of Economic Geology, 1977) Loucks, R. G.; Bebout, Don G.; Galloway, William E.
Reservoir quality of lower Teritary sandstone reservoirs along the Texas Gulf Coast is controlled by sandstone depositional environment, mineralogical composition, and consolidation history (compaction, cementation, and leaching). In general, shallow reservoirs have primary porosity that is reduced by compaction andcementation, whereas deeperreservoirs result from late subsurface leaching. Frio sandstones have the following idealized consolidation history: Near-surface to shallow subsurface compaction and cementation stage (0 to 4,000 feet ±) starts with early feldspar leaching and replacement by calcite followed by precipitation of poikilotopic pore-filling calcite cement, clay coats and rims, feldspar overgrowths, and initial quartz overgrowths. Sand is compacted until arrested by cementation. Reservoir porosity is reduced from 40 percent to approximately 25 percent. Moderate subsurface cementation stage (4,000 to 8,000 feet ±) consists of general precipitation of quartz overgrowths, localized welding by massive quartz overgrowths, and development of sparrypore-fill calcite cement. Porosity is commonly reduced to 10 percent. Moderate subsurface leaching stage (8,000 to 11,000 feet ±) results in massive leaching of feldspars, volcanic and carbonate rock fragments, and calcite cements. Continued leaching may resurrect porositiesto as high as 30 percent. Deep subsurface cementation stage (> 1,000feet ±)involves reduction of leached porosity by precipitation of pore-filling kaolinite and iron-rich carbonate cements; resulting porosities depend on the amount of this late cement. This rock consolidation history can be modified by residence time in each burial stage, thermal gradient, pore-fluid changes,andmineralogical differences. Deep Frio production, then, is not from simple primary porosity between grains, as in shallow reservoirs, but is from secondary leached porosity.
Summary Hydrogeologic Assessment U.S. Department of Energy Pantex Plant, Carson County, Texas
(1995) Gustavson, Thomas C.; Bebout, Don G.; Bennett, P. C.
In 1990, the Bureau of Economic Geology (BEG) and the Department of Geological Sciences (DOGS) at The University of Texas at Austin and the Water Resources Center (WRC) at Texas Tech University began a five-year program, funded by the Department of Energy (DOE) through the Governor's Office of the State of Texas, to characterize the geohydrology of Pantex Plant. The purpose of this work, which is summarized in this report, was to provide data and information that would assist in the remediation of contaminated sites at Pantex and support the State of Texas in its review of the Department of Energy's (DOE's) remediation program. The results of this investigation describe the physical setting and heterogeneities that control movement and distribution of contaminants and the processes that affect rates and fate of contaminants. The fate and distribution of contaminants, the selection and application of appropriate remediation approaches, the evaluation of the effectiveness of remediation technologies, and the proper monitoring of the affected environment all depend on knowledge of the controls and rates of active processes at Pantex Plant.
Technical Support for Geopressured Geothermal Well Activities in Louisiana Annual Report
(1982) Bebout, Don G.; Bassiouni, Zaki; Carver, Dale R.; Groat, C. G.; Pilger, R. H ., Jr.; Wrighton, Fred M.
The rationale previously developed and utilized in interpreting various databases were outlined in the DOE final report titled "Technical Support for Geopressured-Geothermal Well Activities in Louisiana" (August 31, 1981), authored by Fred M. Wrighton, Don G. Bebout, Dale R. Carver, Charles G. Groat, and Adrain E. Johnson, Jr., under Contract No. DE-AS05-78ET27160. Due to the importance of the concepts presented in the previous report for developing an assessment evaluation program, much of the text and illustrations have been repeated for the convenience of the reader. However, the assessment techniques and calculations presented in this report are new. Estimates of the in-place methane resource in the geopressured zone of the U.S. Gulf Coast have varied widely, ranging from less than 1000 trillion cubic feet (TCF) to 49,000 TCF. The most recent assessment for onshore Texas, conducted by Gregory, Dodge, Posey, and Morton in 1981, estimated a total of 690 TCF. Well logs from deep oil and gas wells served as the primary data source for all assessment studies, although the interpretation of these logs varied significantly. In this study focusing on Louisiana, the methods and results were found to compare favorably with those of Gregory and others for Texas. The assessment included the Wilcox, Frio, and Miocene formations. Constructing regional cross-sections across the south Louisiana Gulf Coast was a prime objective to aid in assessing the total solution-methane resource in place. These cross-sections provided point sources of information from key wells and offered insights into the significance of each well through logical correlations with others on the section. Additionally, detailed studies of smaller areas conducted at LSU and other institutions throughout the Gulf Coast were considered, with data from these studies also contributing to the assessment. The total area under consideration in south Louisiana exceeds 18,000 square miles, with geopressured formations including the Wilcox (1692 square miles), Frio (5200 square miles), and Miocene. Parameters considered in this assessment included pressure, sandstone volume, porosity, temperature, and salinity.
Wave-dominated deltaic systems of the Upper Cretaceous San Miguel Formation, Maverick Basin, south Texas
(1979-05) Weise, Bonnie R.; Bebout, Don G.
Sandstone units of the Upper Cretaceous San Miguel Formation in South Texas are wave-dominated deltaic sequences deposited during a major marine transgression. San Miguel sediments were deposited in the Maverick Basin within the Rio Grande Embayment. Cross sections and sandstone maps reveal that during deposition of the San Miguel Formation, the Maverick Basin consisted of two subbasins. A western subbasin received sediments from the northwest; the eastern subbasin received sediments from the north. Net-sandstone patterns show that the thickest parts of the sandstone bodies are generally strike oriented; where not eroded, updip sand-feeder systems are indicated by dip-aligned components. The San Miguel deltas vary considerably in morphology and make up a spectrum of wave-dominated delta types. Modern analogs of these San Miguel deltas include the Rhone, Nile, Sao Francisco, Brazos, Danube, Kelantan, and Grijalva deltas. Final sandstone geometries depended on three primary factors: (1) rate of sediment input, (2) wave energy, and (3) rate of sea-level change. Delta morphology was determined by all three factors, but the degree of reworking of deltaic sediments after delta abandonment was determined by wave energy and rate of transgression. The most common vertical sequences in the San Miguel coarsen upward from silt and clay to fine sand. Burrows are the dominant structures. The few primary structures are of small scale; large-scale cross beds are observed only in outcrop. Strandplain or barrier-island facies sequences, which prevail in most wave-dominated deltaic deposits, are incomplete in the San Miguel. In most places, only the lower shoreface is preserved. The upper parts of the sequences, which normally bear large-scale primary structures, were lost by marine reworking during subsequent transgressions. Intense burrowing destroyed any primary structures at the tops of the truncated sequences. Most of the San Miguel sandstones are arkoses. Cements include sparry and poikilotopic calcite, quartz overgrowths, feldspar overgrowths, illite rims, and kaolinite. The primary destroyers of porosity are the two types of calcite cement, which tend to completely cement the coarsest, best sorted, and originally most porous zones of the San Miguel vertical sequences. Zones of secondary porosity resulted from leaching of shell material, calcite cement, and feldspars. Laterally, the zones of either high secondary porosity or calcite cementation are unpredictable.