83 research outputs found
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Petrophysical Characterization of the South Cowden Grayburg Reservoir,Ector County, Texas
Reservoir performance of the South Cowden Grayburg field suggests that only 21 percent of the original oil in place has been recovered. The purpose of this study is to construct a realistic reservoir model to be used to predict the location of the remaining mobile oil. Construction of reservoir models for fluid-flow simulation of carbonate reservoirs is difficult because they typically have complicated and unpredictable permeability patterns. Much of the difficulty results from the degree to which diagenetic overprinting masks depositional textures and patterns. For example, the task of constructing a reservoir model of a limestone reservoir that has undergone only cementation and compaction is easier than constructing a model of a karsted reservoir that has undergone cavern formation and collapse as well as cementation and compaction.
The Permian-age carbonate-ramp reservoirs in the Permian Basin, West Texas, and New Mexico, are typically anhydritic dolomitized limestone. Because the dolomitization occurred soon after deposition, depositional fabrics and patterns are often retained, and a reservoir model can be constructed using depositional concepts. Recent studies of the San Andres outcrop in the Guadalupe Mountains (Kerans and others, 1994; Grant and others, 1994) and the Seminole San Andres reservoir in the Permian Basin (Lucia and others, 1995) illustrate how depositional fabrics and patterns can be used to construct a reservoir model when depositional features are prominent. South Cowden field, Ector County, Texas, is a Grayburg (Permian age) anhydritic dolomite reservoir similar to many other Permian reservoirs in the Permian Basin. However, the diagenetic overprint has advanced so much that in some parts of the field, depositional patterns and fabrics no longer can be used to predict and model permeability. In this paper, we develop a reservoir model that includes areas where depositional patterns are useful and areas where they are not useful because diagenetic overprinting masks depositional patterns.Bureau of Economic Geolog
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Geoscience/Engineering Characterization of the Interwell Environment in Carbonate Reservoirs Based on Outcrop Analogs, Permian Basin, West Texas and New Mexico - Petrophysical Characterization of the South Cowden Grayburg Reservoir, Ector County, Texas
Reservoir performance of the South Cowden Grayburg field suggests that only 21 percent of the original oil in place has been recovered. The purpose of this study is to construct a realistic reservoir model to be used to predict the location of the remaining mobile oil. Construction of reservoir models for fluid-flow simulation of carbonate reservoirs is difficult because they typically have complicated and unpredictable permeability patterns. Much of the difficulty results from the degree to which diagenetic overprinting masks depositional textures and patterns. For example, the task of constructing a reservoir model of a limestone reservoir that has undergone only cementation and compaction is easier than constructing a model of a karsted reservoir that has undergone cavern formation and collapse as well as cementation and compaction.
The Permian-age carbonate-ramp reservoirs in the Permian Basin, West Texas, and New Mexico, are typically anhydritic dolomitized limestone. Because the dolomitization occurred soon after deposition, depositional fabrics and patterns are often retained, and a reservoir model can be constructed using depositional concepts. Recent studies of the San Andres outcrop in the Guadalupe Mountains (Kerans and others, 1994; Grant and others, 1994) and the Seminole San Andres reservoir in the Permian Basin (Lucia and others, 1995) illustrate how depositional fabric and patterns can be used to construct a reservoir model when depositional features are retained.Bureau of Economic Geolog
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RCRL Studies of Thief Zones in SACROC Field
Geologic models of the northern platform of Sacroc have been constructed over several years (2001–present) by the Reservoir Characterization Research Laboratory (RCRL). These models show a complex stratigraphy of deposition, exposure (diagenesis), and erosion. Canyon units were deposited as depositional cycles, and the latest Canyon cycles have been heavily eroded. The Cisco units are composed of debris flows, biohermal buildups, and grain-dominated units representing many significant sea-level changes, culminating in a major exposure event before being engulfed in carbonate muds of Wolfcamp age.
Geologic models have been converted to petrophysical models by RCRL using the rock fabric method. Porosity-permeability transforms have been defined for each stratigraphic unit using core data and thin-section analyses. Geologic models have been converted to porosity and permeability models using these transforms.
Kinder Morgan has initiated a CO2 flood in the northern platform area. The company's injection program has uncovered numerous intervals in which the rate of injection is significantly higher than expected from the petrophysical model. These intervals are referred to as void space conduits by Kinder Morgan and as thief zones in this report.
The problem facing Kinder Morgan is that the large volume of injected fluid taken by thief zones significantly decreases the volume of remaining-oil saturation contacted by injected fluids, resulting in poor recovery. This report summarizes efforts to explain the geological and petrophysical nature of these thief zones through an exhaustive study of core and log data from well 37-11.
Thief zones are defined as having significantly higher flow rates than expected from matrix properties. At Sacroc, these zones are located by injection profiles, and the injection profile from 37-11 shows high variability in injection volume. Using core data, we calculated kh values for each perforated interval, as well for each injection and no-injection interval within each set of perforations. A positive relationship between kh and water injection is assumed. Unfortunately, in 37-11 only a polymer injection profile was available for this study. A positive relationship between kh and polymer injection is probably true as well.Bureau of Economic Geolog
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Analysis of Core Data-Kinder Morgan SU 228-4A
The Kinder Morgan SU 228-4A well, located in the south part of Sacroc field, Scurry County, Texas, was cored between the depths of 6,989 and 7,009 ft. The basic objective for this study is to describe the saturation profile in the bottom Sacroc reservoir. In other words, is there a transition zone or a residual oil zone (ROZ) at the base?
Porosity and permeability were measured on core plugs, and a cross-plot of the results is illustrated in figure 1. The core was slabbed, and a basic core description prepared (fig. 2). The core is mainly a fossil wackestone with two thick beds and one thin bed of grain-dominated packstone (gdp) and one debris-flow interval. Some of the wackestone is highly stylolitized with associated tension gashes. Gdp beds are interpreted to be grain flows into deep-water muddy sediment. Thin sections were prepared from the ends of the core plugs; however, they are of poor quality and only a basic description was done to validate the core description.Bureau of Economic Geolog
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Rock-Fabric/Petrophysical Classification of Carbonate Pore Space for Reservoir Characterization
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.Bureau of Economic Geolog
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Rock-Fabric Petrophysical Analysis of Core and Wireline-Log Data Haradh 101 and Haradh 106 Ghawar Field, Saudi Arabia
Analysis of thin sections and core data demonstrates that rock fabrics can be grouped into petrophysical fields defined by porosity and permeability. Grainstones and large crystal dolostones fall within the petrophysical class 1 field of Lucia (1995). Permeability increases with increasing dolomite crystal size. The class 1 field is enlarged slightly to include large crystal dolostones with crystal sizes ranging up to 300 microns. Grain-dominated and dolomitic mud-dominated fabrics containing more than 25 percent dolomite fall into the petrophysical class 2 field. The dolomitic mud-dominated fabrics plot in the class 2 field because progressive dolomitization increases pore size by increasing porosity in the intercrystal mud and by creating intercrystal pore space. Mud-dominated fabrics having less than 25 percent dolomite are mostly dense but, when permeable, plot in the petrophysical class 3 field. A global relationship between rock-fabric petrophysical class, interparticle porosity, and permeability that does not require fabrics being divided into specific petrophysical classes has been developed and is used in this analysis.
Permeability can be estimated from wireline logs according to the rock-fabric method. Interparticle porosity is estimated by subtracting total porosity from separate-vug porosity, which, in turn, is estimated from transit-time-porosity cross plots. Petrophysical classes can be identified from a cross plot of water saturation and porosity. The wells are far enough above the free-water level that reservoir height is not an important consideration. We identified boundaries between rock-fabric classes and multiple-regression analysis, using equations of the boundary lines, resulted in a relationship between petrophysical class, saturation, and porosity. Permeability is calculated by substituting log-calculated interparticle porosity and log-calculated petrophysical class into the global transform equation. These calculations compare well with core data and retain high and low permeability values.Bureau of Economic Geolog
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Integrated Outcrop and Subsurface Studies of the Interwell Environment of Carbonate Reservoirs: Clear Fork (Leonardian-Age) Reservoirs, West Texas and New Mexico
This is the final report of the project ''Integrated Outcrop and Subsurface Studies of the Interwell Environment of Carbonate Reservoirs: Clear Fork (Leonardian-Age) Reservoirs, West Texas and New Mexico'', Department of Energy contract no. DE-AC26-98BC15105 and is the third in a series of similar projects funded jointly by the U.S. Department of Energy and The University of Texas at Austin, Bureau of Economic Geology, Reservoir Characterization Research Laboratory for Carbonates. All three projects focus on the integration of outcrop and subsurface data for the purpose of developing improved methods for modeling petrophysical properties in the interwell environment. The first project, funded by contract no. DE-AC22-89BC14470, was a study of San Andres outcrops in the Algerita Escarpment, Guadalupe Mountains, Texas and New Mexico, and the Seminole San Andres reservoir, Permian Basin. This study established the basic concepts for constructing a reservoir model using sequence-stratigraphic principles and rock-fabric, petrophysical relationships. The second project, funded by contract no. DE-AC22-93BC14895, was a study of Grayburg outcrops in the Brokeoff Mountains, New Mexico, and the South Cowden Grayburg reservoir, Permian Basin. This study developed a sequence-stratigraphic succession for the Grayburg and improved methods for locating remaining hydrocarbons in carbonate ramp reservoirs. The current study is of the Clear Fork Group in Apache Canyon, Sierra Diablo Mountains, West Texas, and the South Wasson Clear Fork reservoir, Permian Basin. The focus was on scales of heterogeneity, imaging high- and low-permeability layers, and the impact of fractures on reservoir performance. In this study (1) the Clear Fork cycle stratigraphy is defined, (2) important scales of petrophysical variability are confirmed, (3) a unique rock-fabric, petrophysical relationship is defined, (4) a porosity method for correlating high-frequency cycles and defining rock-fabric flow layers is described, (5) Clear Fork fractures are described and geomechanical modeling of fractures is investigated, and (6) most importantly, new statistical methods are developed for scaleup of petrophysical properties from the core to the layer scale and for retaining stratigraphic layering in simulation models
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Characterization of Facies and Permeability Patterns in Carbonate Reservoirs Based on Outcrop Analogs
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.Bureau of Economic Geolog
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San Andres/Grayburg Reservoir Characterization Research Laboratory
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.Bureau of Economic Geolog
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Geoscience/Engineering Characterization of the Interwell Environment in Carbonate Reservoirs Based on Outcrop Analogs, Permian Basin, West Texas and New Mexico.
The objective of this project is to investigate styles of reservoir heterogeneity found in low permeability pelleted wackestone/packstone facies and mixed carbonate/clastic facies found in Permian Basin reservoirs by studying similar facies exposed in the Guadalupe Mountains. Specific objectives for the outcrop study include construction of a stratigraphic framework, petrophysical quantification of the framework, and testing the outcrop reservoir model for effects of reservoir heterogeneity on production performance. Specific objectives for the subsurface study parallel objectives for the outcrop study. Subsurface Activities - We continue to prepare two final reports that summarize research results of the South Cowden Field study. One report summarizes results of the petrophysical characterization research, and one summarizes results of the fluid-flow modeling research. Outcrop Activities - We also continue to prepare the final report, which summarizes the research results of the Grayburg outcrop reservoir study
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