10 research outputs found
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Enhanced gas recovery from watered-out reservoirs : Port Arthur field, Jefferson County, Texas
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Geopressured Geothermal Fairway Evaluation and Test Well Site Location Frio Formation, Texas Gulf Coast
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 300°F. Several geothermal fairways were identified as a result of this Frio study.Bureau of Economic Geolog
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Exploration and Production Program for Locating and Producing Prospective Aquifers Containing Solution Gas and Free Gas- Texas Gulf Coast
This project was designed to locate and evaluate a prospective watered-out gas reservoir in the Texas Gulf Coast inland area. The prospective reservoir was to be suitable for application of enhanced gas recovery methods for producing the unconventional gas that remained in the reservoir after primary gas production ceased. A test well site would be located within a favorable prospect area.
Previous work conducted by the Bureau of Economic Geology for the U.S. Department of Energy focused on the selection of test well sites in the Frio Formation and Wilcox Group of the Texas Gulf Coast. These studies were intended to make use of thermal energy, mechanical energy, and gas dissolved in formation waters by producing large volumes of hot water from deep, highly pressured formations. In this project, funded by the Gas Research Institute, interest shifted to locating prospective reservoirs containing significant quantities of free gas in addition to the gas dissolved in the water. Abandoned watered-out reservoirs and wet zones where large amounts of water must be produced to obtain the gas by co-production were identified.
The present project, funded by the Gas Research Institute, shows their continuing interest in unconventional gas and in developing prospects that are favorable for co-production of gas and water from watered-out gas reservoirs. Guidelines used to screen gas fields along the Texas Gulf Coast resulted in the selection of the Port Arthur field, Jefferson County, Texas, as a suitable prospect for application of enhanced gas recovery methods. Several watered-out gas sandstones in this field have excellent reservoir characteristics. All 18 wells in the field have been plugged and abandoned by previous operators; hence, leasing problems should be simplified. Abundant shallow Miocene sands in the area are available for salt-water disposal.
The "C" reservoir interval, located at an average depth of 11,130 ft, received the most extensive evaluation. Predicted gas recovery by natural flow is 5.1 billion standard cubic feet as reservoir pressure declines from 6,632 to 4,309 psig. A sample economic analysis showed a net present worth of $968,000 and a payout time of 3 years. This prospect has the potential to be economically profitable in addition to being a good research and development test for evaluating co-production techniques.
It is recommended that a co-production well be drilled and tested on a site near the Meredith No. 2 Doornbos (Well 14).Bureau of Economic Geolog
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Exploration and Production Program for Locating and Producing Prospective Aquifers Containing Solution Gas and Free Gas Texas Gulf Coast - Annual Report
The Port Arthur field in Jefferson County, Texas, has been identified as a promising candidate for secondary enhanced gas recovery methods due to its multiple watered-out gas reservoirs, thick aquifers, and gas stringer sandstones at depths ranging from 10,850 to 11,700 feet. Sidewall core data indicate an average porosity of 30 percent and average permeability of 60 millidarcies (md).
Reservoir simulation studies suggest that approximately 3.91 billion standard cubic feet of unconventional gas can be recovered through natural flow from the 11 C" sandstone over a 10-year period, by reducing reservoir pressure from 6,500 to 4,018 pounds per square inch gauge (psig). The break-even gas price is estimated to be $3.45 per thousand standard cubic feet for a 15-percent rate of return.
Additional gas recovery opportunities exist through co-production from other sandstones and by further reducing reservoir pressure using artificial lift methods. It is recommended to drill a design test well to a depth of 11,650 feet at a location near the Meredith No. 2 Doornbos (Well No. 14). This test well will help evaluate the feasibility and effectiveness of secondary enhanced gas recovery techniques in the Port Arthur field.Bureau of Economic Geolog
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Prospectus for a Design Well in the Blessing Area Matagorda County, Texas
In recent years, the Bureau of Economic Geology has conducted regional subsurface studies of the Wilcox Group and Frio Formation of Texas as part of the U. S. Department of Energy's assessment of deep geopressured geothermal resources along the Gulf Coast. These studies resulted in two reports (Bebout and others, 1978; 1979) that describe several areas in Texas where temperatures are greater than 300°F and where the geology and reservoir conditions are suitable for resource testing by a design well.
Throughout the Texas Coastal Plain, the 300°F isotherm generally occurs at depths ranging from 12,000 to 16,000 ft. The overlying geopressured sediments represent a substantial portion of the sedimentary column that contains significant quantities of entrained methane, making them a significant portion of the resource base (Gregory and others, 1980). The lower temperatures and pressures of these shallow geopressured sediments result in lower methane solubility, but drilling costs would be substantially lower, and perhaps reservoir quality would be better in comparison to the deep geopressured intervals. Although the latter condition has not been substantiated, several areas that are geologically favorable for testing shallow geopressured aquifers with temperatures less than 300°F were identified in a recently completed study (Weise and others, 1980) funded by the Gas Research Institute.
The Blessing Prospect (fig. 1), one of the shallow prospects in Matagorda County, Texas, is presented in this prospectus as a candidate for the DOE design well program. The prospectus focuses on the geological and engineering aspects of the test site. Although legal and environmental considerations are mentioned, they have not been studied in detail and additional work would necessarily follow if the prospect is approved for drilling and testing. Likewise, a drilling program and an economic analysis would be necessary before final approval of a design well.Bureau of Economic Geolog
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Study Effects of Geopressured-Geothermal Subsurface Environment on Elastic Properties of Texas Gulf Coast Sandstones and Shales Using Well Logs, Core Data, and Velocity Surveys
Relations between porosity and permeability for the Pleasant Bayou wells were determined from conventional core data. Porosities from the time-average equations required compaction correction factors of 1.9 in hydropressured sandstones and 1.0 in geopressured sandstones. Best average permeabilities in the geopressured zone were found in the primary production interval 14,687 to 14,716 ft (4,477 to 4,485 m). Average density gradients were 2.106 x 10-3 and 2.688 x 10-3 (gm/cm3)/100 ft in sandstones and shales, respectively.
Compressional (P-wave) and shear (S-wave) velocities from the long-spaced sonic log and bulk densities from the formation density log were used to compute in-situ elastic moduli, Poisson's ratio, Vp / Vs, and bulk compressibility in two intervals of deep geopressured sandstone and shale in No. 2 Pleasant Bayou. Most computed values of these parameters seem reasonable.
Improved accuracy of travel times from the long-spaced sonic log should permit more accurate depth-to-time correlation with seismic data. However, wave theory from Biot (1956) and Geertsma (1961) predicts dispersion at well-log frequencies that may introduce velocity errors of 1.5 to 3.6 percent in sandstones with high porosity and permeability.
High reflection coefficients at interfaces between shales and brine-saturated sandstones indicate that seismic reflection methods may be able to detect high-quality reservoirs with enhanced dissolution porosity in deep Tertiary sandstones.Bureau of Economic Geolog
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Geothermal Resources, Wilcox Group, Texas Gulf Coast
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 300°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.Bureau of Economic Geolog
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Assessment of Unconventional Gas Resource in Texas,oDispersed Gas Project GRI Contract No. 5080-321-0398 August- October
The assessment of various gas resources in Texas, including geopressured sandstones, co-production of gas and water, hydropressured sandstones, undiscovered gas, and wet gas-bearing shale, provides valuable insight into the potential reserves and recovery factors for each resource category. Here's a summary of the key findings:
1. **Geopressured Sandstones:**
- In-place solution gas is estimated to be 690 trillion cubic feet (Tcf) with a recoverable gas of 28 Tcf, representing about 4% of the in-place solution gas.
- Distribution of the resource is tabulated by formation, subdivision, and major fault zones.
2. **Co-production, Gas, and Water:**
- This assessment considers non-associated natural gas in onshore and offshore Texas, with recoverable unconventional free gas calculated based on original gas-in-place, proven gas reserves, cumulative primary gas production, and recovery factors.
3. **Hydropressured Sandstones (or Aquifers):**
- In-place solution gas data are provided for various areas in Texas, assuming a 3% recovery factor.
4. **Undiscovered Gas:**
- Data from various sources are used to estimate undiscovered gas reserves, assuming a recovery factor of 10% of the original gas-in-place.
5. **Wet Gas-Bearing Shale:**
- Estimated recoverable gas in onshore and offshore Texas is 2.7 Tcf, representing about 10% of the recoverable solution gas estimated for geopressured sandstones.
6. **Probability Factors:**
- Probability factors are used to assess the reliability and accuracy of the data used in the assessment, providing insights into the confidence levels associated with the estimated reserves.
Overall, the assessment provides valuable information for understanding the potential gas resources in Texas and the factors influencing their recoverability.Bureau of Economic Geolog
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Geopressured Geothermal Prospects and Test Well Sites Wilcox Group and Frio Formation, Texas Gulf Coast
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.Bureau of Economic Geolog
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Geologic Studies of Geopressured and Hydropressured Zones in Texas: Test-Well Site Selection
The primary objective achieved in this project was to identify sites for test wells capable of long-term production of methane-bearing water from the shallow geopressured and deep hydropressured zones. The process of test-well site selection involved several steps, each contributing to the basic knowledge of shallow geopressured and deep hydropressured aquifers.
First, zones within the geopressured and deep hydropressured section of the Texas Gulf Coast Tertiary were defined based on pressure gradients and temperatures. Next, high-sandstone corridors, corresponding to the trends of the Wilcox Group and Frio Formation, were identified for each of these zones. Five fairways, or areas of greatest net-sandstone thickness, were located within the corridors. Areas most prospective for testing entrained methane resources in the shallow geopressured and deep hydropressured zones were identified in each fairway. Finally, test sites were selected in four of the prospect areas: the Blessing Prospect in Matagorda County, the Nueces Bay and Corpus Channel Prospects in San Patricio and Nueces Counties, and the Sarita Prospect in Kleberg County.
Knowledge gained from these geologic studies and subsequent testing will be significant in (1) evaluating the technical and economic feasibility of producing solution gas from the shallow geopressured and deep hydropressured zones, and (2) comparing these zones with deeper, hotter geopressured zones (studied previously in DOE-funded projects) as sources of entrained methane.Bureau of Economic Geolog