Stratigraphy and Depositional Systems of the Frontier Formation and Their Controls on Reservoir Development, Moxa Arch, Southwest Wyoming

By controlling sandstone continuity and detrital clay content, depositional systems influence reservoir development in low-permeability gas-bearing sandstones of the Upper Cretaceous Frontier Formation along the Moxa Arch in the Green River Basin, southwest Wyoming. Original depositional porosity and permeability are highest in clean Frontier sandstones, which even after diagenetic modification comprise the most prolific reservoirs. The Frontier was deposited in a fluvial-deltaic system, in which most reservoirs lie in fluvial channel-fill and marine shoreface sandstone facies. The fluvial channel-fill sandstones form southeast-trending belts, which are a few miles wide, several tens of feet thick, and separated by interchannel shale and sandy shale. Within the channel belts, clean sandstone occurs as discontinuous lenses up to 20 feet thick that are interlayered and laterally gradational with mud-clast-rich shaly sandstone. The marine shoreface facies forms a continuous northeast-thinning sheet of sandstone, 40 to 120 feet thick. Clean sandstone is best developed near the top of the shoreface facies in northeast-thinning trends 5 to 40 feet thick.Bureau of Economic Geolog

Hydrocarbon Production and Potential of the Distal Frio Formation, Texas Coastal Zone and Shelf

The distal Frio Formation along the Texas Coastal Zone and offshore has yielded 680.85 million barrels of oil and 6.54 trillion ft3 of gas from 153 fields that range in size from 1 to 140 million barrels of oil equivalent. To evaluate the exploration potential of the distal Frio extending deep beneath the Federal Outer Continental Shelf, petroleum production data, regional reservoir-quality and temperature/pressure conditions, and characterization of typical fields were integrated with Galloway's (1986) description of stratigraphy, depositional systems, and structural framework. The most prospective locations for distal Frio exploration are in the Mustang Island and northeastern Galveston offshore areas, extending as far as 15 mi (24 km) seaward of the 3-league line (Outer Continental Shelf boundary). The North Padre Island offshore area has moderate exploration potential. Significant new discoveries will be deep (9,000 to 16,000 ft [2,740 to 4,880 m]), high-pressure, dry-gas-dominated reservoirs in thin, distal deltaic, strike-reworked delta-margin and distal shoreface/shelf sandstones that will potentially yield 1 to 100 billion ft3 of gas annually for as long as 10 years.Bureau of Economic Geolog

Consolidation of Geologic Studies of Geopressured-Geothermal Resources in Texas

The Pleasant Bayou C-zone geopressured-geothermal reservoir is currently undergoing long-term production testing. Using all available deep-well data and building on broad-based previous work, we constructed a detailed geologic characterization of the C-zone reservoir, including sandstone geometry and continuity, porosity distribution, depositional facies interpretation, and structural configuration. This characterization formed the basis for calculating total sandstone volume and effective pore volume of the reservoir and for constructing models for use in numerical simulations. Total effective pore volume of the C-zone reservoir is estimated to be between 6.2 and 6.6 billion barrels. With respect to the test well, one-third of this volume is proximal (within about 3 mi), and two-thirds are remote. Geologically based reservoir volume and models will be useful in predicting long-term well performance and interpreting pressure and production trends during the testing program. We are monitoring pressures in deep gas wells in Chocolate Bayou field to detect possible changes that can be related to production at the Pleasant Bayou test well. No wells produce gas directly from the C-zone reservoir, but several do produce from thin, overlying sandstones, which may be in contact with the perforated interval. Gas well pressure data are reported semiannually and must be monitored for several years to obtain meaningful trends. At a depth of 20,200 ft, the DOE Hulin No. 1 well in southwestern Louisiana penetrates a 550-ft-thick sandstone, which is the deepest known Gulf Coast geopressured-geothermal reservoir. Although the lack of deep well control has precluded detailed mapping, regional stratigraphic context and log response suggest that the Hulin reservoir was deposited in a submarine canyon or proximal submarine fan on the lower Miocene continental slope. Testing the Hulin reservoir will offer a unique opportunity for research and resource evaluation.Bureau of Economic Geolog

Consolidation of Geologic Studies of Geopressured-Geothermal Resources in Texas

Hydrochemical data obtained from samples of brine produced from the Gladys McCall Zone 8 sandstone reservoir were used to estimate the importance of shale dewatering as a contribution to ultimate reservoir volume. Changes in chloride concentration of produced brines with time were generally small and close to analytical margins of error, but some correlation between production-related pressure drawdown and declining chlorinity was detected. More rigorous analysis of brine composition and source was hindered by nonstandardized sampling and analytical procedures. Geologic data suggest that sandstone interconnection is a more important source of extra reservoir volume than is shale dewatering at the Gladys McCall site. Methods for more definitively determining the effects of shale dewatering and reservoir interconnectedness include direct sampling and chemical analysis of shale water, pressure monitoring and fluid sampling in multiple reservoirs in a single well or a well field, and sidetrack drilling and coring. Petrographic analysis was used to document the effects of experimental compaction on core samples from geopressured-geothermal reservoirs. Experimental compaction simulates the increasing effective stress within these reservoirs as fluid pressures decline during production. Inelastic compaction and brittle failure (fracturing) are closely related to sandstone composition. Sandstones that contain abundant ductile rock fragments and clay minerals undergo large compaction-induced porosity reductions and fracture readily at effective stress levels comparable to those generated in the reservoir during high-volume production. Well-indurated, high-quartz sandstones, such as the Gladys McCall Zone 8, are extremely resistant to both inelastic compaction and brittle failure.Bureau of Economic Geolog

Depositional and Structural Challenges of the Wilcox Lobo Natural Gas Trend, South Texas

To increase understanding and utilization of gas resources in the Wilcox Lobo play of South Texas, this report reviews current geological knowledge of the Lobo trend. An additional objective of this report is to identify areas where advancements in geological understanding could lead to substantial improvements in efficient development of the Wilcox Lobo trend natural gas resource. According to published accounts, Lobo sandstones formed in a variety of depositional environments in both shallow and deep marine waters. During and after deposition, the Lobo experienced repeated episodes of erosion, faulting, and diagenesis. Thus, accurate prediction of reservoir sandstone attributes is difficult, and this difficulty is cited by operators as a significant challenge to efficiently targeting the remaining gas resource. Knowledge that would aid in the emergence of this resource includes information on sandstone correlation and accurate zone identification, depositional systems and facies interpretations, controls on fault pattern variability, and, to a lesser extent, recognition of diagenetic patterns and faults and fractures that are below seismic resolution. Geologic challenges of the Lobo trend are opportunities for targeting increasingly smaller and more difficult-to-detect compartments with advanced technology.Bureau of Economic Geolog

Texas Salt Domes--Aspects, Affecting Disposal of Toxic-Chemical Waste in Solution-Mined Caverns

This report represents Phase II of a one-year contract aimed at analyzing technical considerations linked to the potential isolation of toxic chemical waste within solution-mined caverns situated in Texas salt domes. A key objective of Phase II research was to characterize the properties of salt domes that could impact this form of waste disposal.Bureau of Economic Geolog

Technical Issues for Chemical Waste Isolation in Solution-Mined Caverns in Salt Domes

Many factors contribute to assessing the technical viability of isolating chemical waste in solution-mined caverns within salt domes. Our investigation highlights several key factors of primary importance, including geohydrology, engineering considerations, and the stability of the geologic isolation system, encompassing the cavern, cap rock, and surrounding strata. These factors are largely interconnected and mutually dependent. An essential initial step involves detailed mapping of the domal system, including the cap rock, salt stock, and surrounding domed strata, a level of detail often lacking in public sources and geological literature. Postulated release scenarios typically involve waste transport via groundwater, making the direction and rates of groundwater flow critical. Groundwater flow is influenced by various factors such as rock matrix composition, depositional systems, sand-body geometry, and fault patterns. The cap rock serves as a focal point for many domal processes and is a dynamically changing region of a salt dome. Studies on cap-rock properties can help determine whether salt domes are undergoing uplift or dissolution. The cap rock plays a crucial role in either facilitating or impeding dome dissolution and cavern stability. Further research on salt domes should focus on defining the geometry and structure of cap rocks, identifying cap-rock lost-circulation zones, understanding the geometry, structure, and stratigraphy of salt stocks and caverns, assessing salt-cavern stability, and investigating domal geohydrology. In the following sections, we discuss various issues that need to be addressed to evaluate the technical feasibility of isolating chemical waste in solution-mined caverns within salt domes.Bureau of Economic Geolog

Texas Salt Domes: Natural Resources, Storage Caverns, and Extraction Technology

This report reviews natural resources associated with salt domes in Texas. Salt domes provide a broad spectrum of the nation's industrial needs including fuel, minerals, chemical feedstock, and efficient storage space. This report focuses on the development, technology, uses, and problems associated with solution-mined caverns in salt domes. One proposed new use for salt domes is the permanent isolation of toxic chemical waste in solution-mined caverns. As the Texas Department of Water Resources (TDWR) is the State authority responsible for issuing permits for waste disposal in Texas, TDWR funded this report to judge better the technical merits of toxic waste disposal in domes and to gain a review of the state of the art of applicable technology. Salt domes are among the most interesting and intensively studied structural-stratigraphic geologic features. Individual domes may be the largest autochthonous structures on earth. Yet many aspects of salt-dome genesis and evolution, geometry, internal structure, and stratigraphy are problematic. Details of both external and internal geometry of salt stocks and their cap rocks are vague, and information is restricted to the shallow parts of the structure. These facts are all the more surprising considering that salt diapirs dominate the fabric of the Gulf Coastal Province, which is one of the most explored and best known geologic regions on earth. This report includes information on present and past uses of Texas salt domes, their production histories, and extractive technologies (see also Halbouty, 1979; Hawkins and Jirik, 1966; and Jirik and Weaver, 1976). Natural resources associated with salt domes are dominated by petroleum that is trapped in cap rocks and in strata flanking and overlying salt structures. Sulfur occurs in the cap rock of many domes. Some cap rocks also host potentially valuable Mississippi Valley-type sulfide and silver deposits. Salt is produced both by underground mining of rock salt and by solution brining. The caverns created in salt by solution mining also represent a natural resource. The relative stability, economics, location, and size of these caverns make them valuable storage vessels for various petroleum products and chemical feedstocks.Bureau of Economic Geolog

Subsurface Oil-Shale Samples of the Lower Permian Wolfcampian and Lower Leonardian Mudrocks and Upper Leonardian Spraberry Formation, Midland Basin, West Texas: Core Sampling for Measured Vitrinite-Reflectance (Ro) Determination

This report summarizes activities carried out by the Bureau of Economic Geology (BEG) during fiscal year (FY) 2014 for the National Coal Resources Data System State Cooperative Program (NCRDS project). In a continuation of the sampling strategy for measured vitrinite-reflectance (Ro) determination initiated 5 years ago (Hentz and others, 2009) and conducted during the following four years (Hentz and others, 2010, 2011, 2012, 2014), this report provides a collection of oil-shale samples from the prolific Lower Permian Wolfcampian and lower Leonardian mudrocks and upper Leonardian Spraberry Formation of the Midland Basin in West Texas (Fig. 1).Bureau of Economic Geolog

Geologic Controls on Reservoir Properties of Low Permeability Sandstone, Frontier Formation, Moxa Arch, Southwest Wyoming

This report examines the influence of stratigraphy, diagenesis, natural fractures, and in situ stress on low-permeability, gas-bearing sandstone reservoirs of the Upper Cretaceous Frontier Formation along the Moxa Arch in the Green River Basin, southwestern Wyoming. The main stratigraphic controls on distribution and quality of Frontier reservoirs are sandstone continuity and detrital clay content. The Frontier was deposited in a fluvial-deltaic system, in which most reservoirs lie in marine upper shoreface and fluvial channel-fill sandstone facies. The major causes of porosity loss in Frontier sandstones during burial diagenesis were mechanical and chemical compaction and cementation by calcite, quartz, and authigenic clays. Despite extensive diagenetic modification, reservoir quality is best in facies that had the highest porosity and permeability at the time of deposition. Natural fractures are sparse in Frontier core, but outcrop studies show that fractures commonly are in discrete, irregularly spaced swarms separated by domains having few fractures. Natural fracture swarms are potential high-permeability "sweet spots." Stress-direction indicators give highly scattered estimates of maximum horizontal compression direction ranging from north to east or northeast. The scatter may reflect interference of natural fractures with measurements of stress directions, as well as spatially variable stress directions and low horizontal stress anisotropy.Bureau of Economic Geolog