Browsing by Subject "San Andres Formation"

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A Comparison of the Depositional Environment of the San Andres Formation in the Palo Duro Basin to Recent Evaporitic Environments
(1984) Chapman, Jenny Burgen
The safe storage of high-level radioactive waste in a geologic repository requires a detailed knowledge of the properties of the host rock and surrounding beds, and the continuity of these properties. One of the serious problems faced in the characterization of the deep formations under consideration is that sufficiently detailed descriptions cannot be obtained from the small number of widely spaced test holes available. The examination of modern analogs to the formation under consideration can provide important insights into geochemical characteristics and their degree of continuity. The first step in identifying a natural analog is to adequately describe the formation of interest and to determine its environment of deposition. The formation under consideration in the Palo Duro Basin, the San Andres Formation, has been described elsewhere (Presley, 1979a & b; 1980a & b, 1981; Presley and Ramondetta, 1981; Ramondetta, 1981; Handford, 1981a & b; Handford and Wiggins, 1981; Bassett and Palmer, 1981; Bassett and Roedder, 1981; Budnik and Smith, 1982; Roedder, 1982). In the Palo Duro Basin, the San Andres Formation is an evaporite sequence containing halite, anhydrite, carbonates, and mudstones. The lithology of the San Andres and the stratigraphic sequence prior to San Andres deposition indicate that the formation was deposited at the end of a long-term shift from fan-delta, marine shelf, and deep-basin environments during the Pennsylvanian to shallow marine, brine pan, and evaporite conditions during Late Permian time. A modern analog environment should be located in a relatively shallow basin that has already been filled by marine sedimentation and is now a broad shelf undergoing long-term oceanic regression and slow subsidence.
Characterization of Reservoir Heterogenity in Carbonate-Ramp Systems, San Andres/Grayburg Permian Basin
(1991) Kerans, C. (Charles), 1954-; Lucia, F. Jerry; Senger, Rainer K.; Fogg, Graham E.; Nance, Hardie Seay, 1948-; Kasap, Ekrem; Hovorka, Susan D.
This report summarizes research carried out by the Bureau of Economic Geology's San Andres/Grayburg Reservoir Characterization Research Laboratory (RCRL) from September 1988 through September 1990. The goal of the RCRL program was to develop advanced approaches to reservoir characterization for improved recovery of the substantial remaining mobile oil in San Andres and Grayburg reservoirs. Emphasis was placed on developing an outcrop analog for San Andres strata that could be used as (1) a guide to interpreting the regional and local geologic framework of the subsurface reservoirs and (2) a data source illustrating the scales and patterns of variability of rock-fabric facies and petrophysical properties, particularly in lateral dimensions, and on scales that cannot be studied during subsurface reservoir characterization. Areas selected for study were the San Andres exposures of the Algerita Escarpment in the northern Guadalupe Mountains and the Seminole San Andres Unit on the northern margin of the Central Basin Platform. The outcrop-analog research was emphasized because it had received little attention before this study by either industry or academe. Reports in this summary involve (1) outcrop and subsurface geological characterization of the Algerita Escarpment San Andres and the Seminole San Andres Unit (Kerans), (2) correlation of detailed outcrop mapping in order to research cored wells at Lawyer Canyon, Algerita Escarpment (Nance), (3) diagenetic/petrographic analysis of selected upper San Andres facies focusing on the origin of moldic porosity (Hovorka), (4) geologic engineering description of the upper San Andres carbonates at Lawyer Canyon and the upper producing interval at Seminole (Lucia), (5) geostatistical analysis of permeability patterns and stochastic-based finite-difference modeling of the upper San Andres parasequence window (Senger and Fogg), and (6) deterministic finite element modeling of the upper San Andres parasequence window (Kasap). Availability of basic data for these studies is summarized in the appendix.
Diagenesis of the San Andres Formation: Unit 4 Carbonate, G. Friemel and Detten Wells
(1987) Hovorka, Susan D.
Petrographic examination of 71 thin sections from the San Andres unit 4 carbonate reveals a complex diagenetic history. Diagenetic events include precipitation of calcite cement, neomorphic replacement of micrite by sparry calcite, development of moldic porosity, dolomitization, precipitation of halite and anhydrite, minor precipitation of celestite, and replacement of halite by calcite, dolomite, and anhydrite. Porous intervals are recognized within the San Andres unit 4 carbonate, corresponding to partly or completely dolomitized intervals. These diagenetic phases reflect an active history of changes in water composition, suggesting potential for further studies of rock-water relationships.
San Andres/Grayburg Reservoir Characterization Research Laboratory
(1989) Kerans, C. (Charles), 1954-; Lucia, F. Jerry; Fogg, Graham E.
The Bureau of Economic Geology's Reservoir Characterization Research Laboratory project, "Characterization of San Andres and Grayburg Reservoirs," was initiated in September 1988 and has completed the first year of a proposed 2-year program. Substantial progress has been made toward the goals of this program, which are focused on development of advanced approaches to reservoir characterization for improving recovery efficiency of substantial remaining mobile oil resources in these prolific reservoirs. Key research results are in the areas of (1) quantitative description and geostatistical modeling of interwell and reservoir-scale heterogeneity from San Andres outcrops, and (2) preliminary studies on integration of the quantitative outcrop models with a geologic/engineering characterization of the Seminole San Andres Unit. Outcrop geologic studies were carried out at play, reservoir, and interwell scales along the Algerita Escarpment, Guadalupe Mountains, New Mexico. This 17-mile play-scale study area provides a dip-section framework for detailed investigations and serves as an analogous reservoir framework for comparison with producing San Andres fields. Reservoir-scale mapping of a 4-mile dip section of the upper San Andres with measured sections spaced 1,000 to 2,000 ft apart demonstrates the compartmentalization of individual grainstone shoal complexes on the scale of several thousand feet laterally and 50 to 100 ft vertically.
Stratigraphy of Bedded Halite in the Permian San Andres Formation, Units 4 and 5, Palo Duro Basin, Texas
(1985) Hovorka, Susan D.; Luneau, Barbara A.; Thomas, S.
Seven cored wells through the bedded halite of the San Andres Formation have allowed an unusual, detailed analysis of the fabrics in halite. A descriptive classification system identified eight textural types of halite. These are: chevron halite rock, color-banded/vertically oriented halite rock, chaotic mudstone-halite rock, equant muddy halite rock, equant anhydritic halite rock, displacive halite in other sediments, cavity-filling halite cement, and fibrous fracture-filling halite cement. Genetic interpretation of the depositional environment in which halite textures formed resulted from analysis of the relationships between textures and comparison to ancient, modern, and experimental halite analogs. Chevron and color-banded/vertically oriented halite are recognized as textures formed subaqueously as halite precipitated on the floor of brine pools. Chaotic mudstone-halite rock, equant muddy halite rock, equant anhydritic halite rock are recognized as diagenetic alteration products formed by karstification and diagenetic recrystallization occurring at least partly in the subaerial environment. Displacive halite in other sediments, cavity-filling halite cement, and fibrous fracture-filling halite cement are products of precipitation of halite within the sediment during early diagenesis. Very detailed logging of the halite fabrics and anhydrite and mudstone interbeds and partings in the seven cored wells allowed correlation on a meter scale between cores. A basin-wide pattern of alternation between zones of anhydritic halite with preserved brine pool fabrics and zones of halite with mudstone interbeds and altered textures was identified. These alternating zones can be traced as much as 100 km between the wells, providing evidence that the entire study area was one broad low relief evaporitic shelf. Net mud maps of the muddy intervals suggest that the geometry of mudstone beds might be broad, poorly-defined lobes. Isopachs of the anhydrite interbeds show variation in the facies pattern in each genetic cycle. Some anhydrite beds thicken toward southern Swisher County, while others are thickest to the west, in Deaf Smith County.