Browsing by Subject "carbonate rocks"

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Characterization of Facies and Permeability Patterns in Carbonate Reservoirs Based in Outcrop Analogs
(1992) Kerans, C. (Charles), 1954-; Lucia, F. Jerry; Senger, Rainer K.; Fogg, Graham E.; Nance, Hardie Seay, 1948-; Hovorka, Susan D.
More than 13 billion barrels (Bbbl) of mobile oil and 17 Bbbl of residual oil will remain in San Andres and Grayburg reservoirs at abandonment under current development practices. Through the development and application of new recovery technology, a large part of this resource can be recovered. This report focuses on research for the development and testing of new techniques for improving the recovery of this resource. Outcrop and subsurface geologic and engineering data are utilized to develop new methodologies through the integration of geologic observations and engineering data for improving numerical models that predict reservoir performance more accurately. Extensive regional mapping of the 14-mile by 1,200-foot San Andres outcrop, located on the Algerita Escarpment, Guadalupe Mountains, New Mexico, demonstrates that the San Andres carbonate-ramp complex is composed of multiple depositional sequences that have significant basinward shifts in reservoir-quality facies tracts occurring across sequence boundaries. Detailed geologic and petrophysical mapping of three reservoir-quality facies tracts demonstrates that the fundamental scale of geologic description for reservoir characterization is the parasequence and its component rock-fabric-based facies. Descriptions of cores from the Seminole San Andres Unit illustrate that the parasequence is also the fundamental geologic scale for reservoir mapping in the subsurface.
Characterization of Facies and Permeability Patterns in Carbonate Reservoirs Based on Outcrop Analogs
(1993) Kerans, C. (Charles), 1954-; Lucia, F. Jerry; Senger, Rainer K.
More than 13 billion barrels (Bbbl) of mobile oil and 17 Bbbl of residual oil will remain in the San Andres and Grayburg reservoir at abandonment under current development practices. Through the development and application of new recovery technology, a large part of this resource can be recovered. This report focuses on research for the development and testing of new techniques for improving recovery of this resource. Outcrop and subsurface geologic and engineering data are utilized to develop new methodologies through the integration of geologic observations and engineering data for improving numerical models that predict reservoir performance more accurately. Extensive regional mapping of the 14-mile by 1,200-foot San Andres outcrop, located on the Algerita Escarpment, Guadalupe Mountains, New Mexico, demonstrates that the San Andres carbonate-ramp complex is composed of multiple depositional sequences that have significant basinward shifts in reservoir-quality facies tracts occurring across sequence boundaries. Detailed geologic and petrophysical mapping of three reservoir-quality facies tracts demonstrates that the fundamental scale of geologic description for reservoir characterization is the parasequence and its component rock-fabric-based facies. Descriptions of cores from the Seminole San Andres Unit illustrate that the parasequence is also the fundamental geologic scale for reservoir mapping in the subsurface.
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.
Dominant Control of Reservoir-Flow Behavior in Carbonate Reservoirs as Determined from Outcrop Studies
(1992) Senger, Rainer K.; Lucia, F. Jerry; Kerans, C. (Charles), 1954-; Ferris, Malcolm Alexander, 1961-
The investigation of carbonate-ramp deposits of the upper San Andres Formation that crop out along the Algerita Escarpment, New Mexico, is a research element of ongoing geologic and petrophysical studies conducted at the Bureau of Economic Geology's Reservoir Characterization Research Laboratory (RCRL). The primary goal of the investigation is to develop an integrated strategy involving geological, petrophysical, geostatistical, and reservoir-simulation studies that can be used to better predict flow characteristics in analogous subsurface reservoirs. Geologic investigations and detailed measurements of petrophysical parameters on continuous outcrop were used to determine not only the vertical distribution of the data but also their lateral distribution, which is typically lacking in subsurface studies. To characterize the complex heterogeneity associated with depositional and diagenetic processes at the interwell scale, detailed permeability data were collected within the overall geologic framework from the outcrop at Lawyer Canyon, Algerita Escarpment, New Mexico (fig. 1). Geologic mapping showed a series of upward-shallowing parasequences (10 to 40 ft thick and several thousand feet long). Parasequence boundaries are typically marked by tight mudstone/wackestone beds that display variable degrees of lateral continuity ranging from several hundred feet to more than 2,500 ft and are potentially important as flow barriers (fig. 2). Within these parasequences, distinct variability of facies and petrophysical characteristics is present at scales well below those of interwell spacing typical for their subsurface counterparts (660 to 1,330 ft). Pore types and permeability-porosity relationships can also be specific to individual parasequences.
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.
Reservoir Characterization Research LaboratoryCarbonate Reservoirs
(1995) Lucia, F. Jerry; Wang, Fred P. ; Kerans, C. (Charles), 1954-
Characterization of a carbonate reservoir for fluid flow simulation is a highly complicated task. What is clear is that the end product must be a three-dimensional numerical image of petrophysical properties: porosity, fluid saturation, permeability, and relative permeability. The principal problems are (1) determining petrophysical values to be imaged and (2) distributing petrophysical values in space. Petrophysical properties are determined by measurements on core and outcrop material, by calculations using wireline log data, and by well tests and tracers. Methods of distributing the petrophysical values usually involve a combination of geologic and statistical modeling. This report emphasizes wireline log calculations and geologic modeling using a rock-fabric approach developed in outcrop studies (Lucia and others, 1992; Senger and others, 1993; Kerans and others, 1994). The approach is to construct a detailed chronostratigraphic framework using sequences of geologic features that are related to water depth and to fill the framework with petrophysical attributes using relationships between rock-fabric and petrophysical properties. Geologic and petrophysical studies of the San Andres Formation in Lawyer Canyon, Algerita Escarpment, Guadalupe Mountains of New Mexico, suggest that (1) petrophysical properties are near-randomly distributed within rock-fabric facies; (2) rock-fabric facies are systematically stacked within high-frequency cycles (HFC's); (3) rock-fabric facies can have significantly different petrophysical properties; (4) vertical changes in properties can be abrupt, whereas lateral changes are gradual; and (5) thin, discontinuous, tight mudstone beds are effective vertical barriers to fluid flow. These findings have been applied to a detailed reservoir characterization study of two sections of the Seminole San Andres Unit operated by Amerada Hess Corporation.
Rock-Fabric/Petrophysical Classification of Carbonate Pore Space for Reservoir Characterization
(1993) Lucia, F. Jerry
The goal of reservoir characterization is to describe the spatial distribution of petrophysical parameters such as porosity, permeability, and saturation. Wireline logs, core analyses, production data, pressure buildups, and tracer tests provide quantitative measurements of petrophysical parameters in the vicinity of the wellbore. These wellbore data must be integrated with a geologic model to display the petrophysical properties in three-dimensional space. Studies that relate rock fabric to pore-size distribution, and thus to petrophysical properties, are key to quantification of geologic models in numerical terms for input into computer simulators. Geologic models are generally based on observations that are interpreted in terms of depositional environments and sequences. In the subsurface, cores and wireline logs are the main source of data for these interpretations. Engineering models are based on wireline log calculations and average rock properties from core analyses. Numerical engineering data and interpretive geologic data are joined at the rock fabric level because the pore structure is fundamental to petrophysical properties, and the pore structure is the result of spatially distributed depositional and diagenetic processes. The purpose of this report is to (1) describe the relationship between carbonate rock fabrics and petrophysical properties, (2) suggest a generic petrophysical classification of carbonate pore space, and (3) determine the important geologic parameters to be mapped to allow accurate quantification of carbonate geologic models.