Geological Circulars

Permanent URI for this collectionhttps://hdl.handle.net/2152/121888

Peer-reviewed geoscience research summaries, targeted on Bureau project areas in Texas and other locations, 1965–2003.

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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.
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.

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Browsing Geological Circulars by Author "Bebout, Don G."