Reservoir Characterization Research Laboratory for Carbonate Studies. Research Plans for 2007

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2 Reservoir Characterization Research Laboratory for Carbonate Studies Research Plans for 2007 Outcrop and Subsurface Characterization of Carbonate Reservoirs for Improved Recovery of Remaining Hydrocarbons Charles Kerans, F. Jerry Lucia, and James W. Jennings, Jr. Co-Principal Investigators Bureau of Economic Geology Scott W. Tinker, Director John A. and Katherine G. Jackson School of Geosciences The University of Texas at Austin

3 Research Plans for 2007 Reservoir Characterization Research Laboratory Outcrop and Subsurface Characterization of Carbonate Reservoirs for Improved Recovery of Remaining Hydrocarbons EXECUTIVE SUMMARY The Reservoir Characterization Research Laboratory (RCRL) for carbonate studies is an industrial research consortium run by the Bureau of Economic Geology (BEG) and the Department of Geological Sciences of the John A. and Katherine G. Jackson School of Geosciences, The University of Texas at Austin (UT). The RCRL s mission is to use outcrop and subsurface geologic and petrophysical data from carbonate reservoir strata as the basis for developing new and integrated methodologies to better understand and describe the 3-D reservoir environment. Funding With this proposal, we invite you to participate in continuing the RCRL Carbonate Reservoirs Research Program. A list of 2006 sponsors can be found at the end of this proposal. In 2007 the annual RCRL Industrial Associates contribution to the program will remain $45,000 per year. RCRL Program The RCRL program, running continuously since 1987, has produced more than 45 external publications, as well as BEG publications, on carbonate reservoir characterization, sequence stratigraphy, petrophysics, geostatistics, and petroleum engineering. RCRL has maintained a membership of between 13 and 18 companies per year. The sponsorship currently has strong interests in a variety of domestic and international carbonate reservoirs ranging in age from Ordovician to Tertiary. This enrollment, supplemented by other grants, supports between three 2

4 and six professional staff members and varying numbers of graduate student research assistants, as well as strong computer, editing, and graphics services. All staff members have extensive industry experience or have worked closely with industry and are well aware of the challenges and questions facing development geoscientists and engineers. Principal Staff Dr. Charles Kerans, Geology Professor, Principal Investigator Mr. F. Jerry Lucia, Geological Engineer, Principal Investigator Dr. James W. Jennings, Jr., Reservoir Engineer, Principal Investigator Dr. Xavier Janson, Geologist Mr. Jerome A. Bellian, Geologist Dr. Daniel Kurtzman, Hydrologist Associate Staff Dr. Fred Wang, Reservoir Engineer Dr. Hongliu Zeng, Geophysicist Graduate Students in RCRL Research Graduate student research, a growing element of the RCRL program, allows us as a group to take on many more projects and visit more field areas than previously possible. This year was the first year that students headed up the review meeting. On the basis of sponsor input we will continue to develop the student research component of the program. Currently we have nine graduate students involved in the RCRL Enzo Achoncha, Jerome Bellian, Jason Clayton, Ned Frost, Beatrix Garcia-Fresca, Ryan Phelps, Ted Playton, Sam Scott, and Adolphus Wilson. If you have any questions on any aspects of the RCRL Carbonate Reservoirs Research Program, please contact Charlie Kerans ( or ckerans@mail.utexas.edu), Jerry Lucia ( or jerry.lucia@beg.utexas.edu), or Jim Jennings ( or jim.jennings@beg.utexas.edu). 3

5 RESEARCH DIRECTIONS FOR 2007 Areas of Research Each year we combine industry input with our own ongoing research plans to develop a set of key geological and engineering research topics. Plans for 2007 are focused on the following areas: Areas of Research (1) Geologic Characterization and Fluid Flow in Nonmatrix Pore Systems (2) Outcrop Studies of Carbonate Heterogeneity Style Platform, Slope, and Basin (3) Subsurface Reservoir Models and Modeling Methods (4) Predictive Dolostone and Limestone Diagenetic Studies (5) Database Information Transfer General Our industry sponsors will continue to receive research results at annual review meetings, in short courses and workshops, during mentoring activities, in publications and CD s, and on our developing members-only RCRL database ( Workshops Many of our sponsoring companies have requested field trips and workshops that present past research results in contrast to the annual review and field trip that presents current results. This request occurs because the flow of new geoscientists to sponsor companies creates a need for training in classical field areas and from short courses that summarize key findings of the consortium. To meet this need we plan to provide a carbonate field trip and reservoir modeling workshop annually to educate those geoscientists who are not fully aware of our technical advances. In 2006 we conducted one reservoir modeling workshop, and we plan to continue this practice by presenting a second modeling workshop in May In addition, we plan to lead a general field trip in April 2007 for our sponsoring companies. 4

6 Mentoring program Direct contact with the technical staff of our sponsoring companies is an important ongoing aspect of our information transfer program. This interaction allows us to test our concepts and methods on real problems, while providing an opportunity for our sponsors to learn how to apply our methods in developing new reserves. Sponsors are encouraged to contact us with projects that could be mutually beneficial. RESEARCH PROGRAM FOR 2007 Geologic Characterization and Fluid Flow in Nonmatrix Pore Systems Permeability modeling is a fundamental problem in reservoir characterization. The RCRL has developed advanced methods of modeling matrix permeability suitable for filling geologic models with petrophysical properties. Modeling of nonmatrix flow, flow in touching-vug pore systems that include fractures, solution-enlarged fractures, large vugs and caverns, and collapse breccias remains a major problem in carbonate reservoir characterization. For the past several years the RCRL has embarked on research to investigate the nature and fluid-flow characteristics of nonmatrix flow by (1) collecting and analyzing large outcrop samples using high-resolution CT scans, (2) mapping touching vugs and matrix porosity in outcrops of karsted carbonate, (3) describing a karsted dolostone reservoir (the San Andres Hobbs Unit), and (4) investigating seismic methods for imaging vuggy pore space, including karst features and moldic grainstones. In 2007 we will continue to research this problem focusing on the following projects. Pipe Creek Outcrop Study In previous years we studied fluid flow in a vuggy rudist rudstone sample collected from the Cretaceous Pipe Creek Reef. High-resolution CT scans and laboratory fluid-flow experiments were conducted with this sample to determine vug-size statistics, vug-connection geometry, permeability, and tracer transport properties. In 2005 we initiated a larger scale study at the Pipe Creek outcrop using two 25-ft wells drilled 5 ft apart. A preliminary air extraction test with these wells indicates connected vugs at the 5-ft scale and an effective permeability of 1 Darcy, 5

7 consistent with whole-core analysis of four core samples from these two wells. We plan additional well tests in 2007 to refine our permeability estimates, and tracer tests to determine the amount of pore space contributing to fluid flow. Lake Medina Outcrop Study In 2007 we plan to continue our study of the Lake Medina outcrop using coupled matrix-fracture fluid-flow modeling in 3D and outcrop characterization of vugs. The outcrop includes vugs that are preferentially located at the intersections of fractures and grainstone layers. We thus hypothesize that the flow rate of groundwater and the rate of dissolution were greatest at these intersections. To test this hypothesis we are constructing 3D fluid-flow models, with fracture porosity and permeability superimposed on a stratigraphic grid of matrix petrophysical properties. Preliminary results indicate that flow-rate maxima do occur at intersections of permeable fractures and grainstone layers, suggesting that the simulated flow-rate field can be a tool for predicting the location of vugs. We plan to study the spatial arrangement and strength of the simulated flow maxima resulting from various combinations of boundary conditions, fracture permeabilities, and matrix heterogeneities. Additional plans for the Lake Medina outcrop study include (1) development of quantitative field methods for surveying vug size, location, density, and connectivity, using both traditional measurements and lidar data; (2) synthesis of the flow-model results and field data to improve modeling of discrete fractures and vugs; and (3) development of scaleup methods to estimate effective flow properties in subsurface models having similar combinations of matrix, fracture, and vug permeability. Regional Study of a Cretaceous Karst Reservoir An extensive karst system is located in Cretaceous carbonates of Central Texas and houses the world-class Edwards aquifer. This aquifer and karst system have been studied extensively but only on a regional scale. We have focused on the 100-ft scale with our study of the Medina roadcut, and have reported results in the past several annual review meetings. In 2007 we propose to extend our study to include other outcrops and roadcuts, as well as numerous quarries and caverns. We intend to use these data to quantify various genetic geometries, scales of touching-vug interconnections, and links between vug development and stratigraphy. 6

8 Franklin Mountain Karst Study Our ability to develop robust geologic models of touching-vug systems and to generate efficient and reliable performance predictions for these rocks remains inadequate. Mapping of breccia bodies over several-square-kilometer areas, such as those exposed in the southern Franklin Mountains in El Paso, Texas, is one way to begin to assess lateral and vertical heterogeneity at reservoir scales. Field mapping of the uppermost El Paso Group (Lower Ordovician), just below the regional Sauk unconformity (30-m.y. time gap) has been conducted and will be incorporated into the recently acquired airborne lidar data set. High-resolution ground-lidar data will continue to be added to the airborne data in order for us to construct high-resolution (3- to 5-cm point spacing), detailed karst-body boundaries in 3D. The objective of this work is to better delineate breccia bodies and reconstruct the events that led up to the emplacement of large laterally and vertically extensive breccia bodies, as related to long-term unconformity and exposure events. Hobbs San Andres Karst Reservoir Study The RCRL approach to understanding carbonate reservoirs is to study outcrop analogs of subsurface reservoirs. For the past few years we have been investigating the stratigraphy, petrophysics, and production characteristics of the Hobbs San Andres reservoir in the Permian Basin, Texas and New Mexico, supported by Oxy Permian. We have reported on our research results at the annual review meetings and plan to continue this investigation toward construction of a realistic simulation model. To that end we plan to further investigate the distribution of nonmatrix flow by studying production characteristics and injection profiles in the lower part of the reservoir, where injection is taking place. Hobbs San Andres Karst Reservoir Model A sequence-stratigraphic model and a rock-fabric petrophysical study of the Hobbs San Andres reservoir were both completed in The petrophysical study confirmed the presence of large permeabilities dominated by touching-vug flow in some parts of the reservoir, and highlighted the importance of injection-profile data in mapping these karst-influenced regions. In 2007 we plan to build a gridded porosity and permeability model of the reservoir to test our ideas on 7

9 model construction in touching-vug settings like Hobbs. The model will combine porosity and matrix permeability modeled in the stratigraphic framework according to our usual rock-fabric and geostatistical methods, with maps of karst-related permeability enhancement generated from injection-profile data. Seismic Modeling of Separate-Vug Pore Space We will continue to develop seismic processing and interpretation strategies to identify and map moldic porosity from 3D seismic data. In 2005 we studied seismic response to vuggy porosity in high-frequency cycle 7 of the Lawyer Canyon outcrop. The study showed that the difference in acoustic properties between separate-vug grainstone and nonvuggy grainstone can generate a large enough impedance contrast to be detected on poststack seismic images. Initial results from modeling amplitude variation with offset (AVO) of the cycle 7 grainstone showed that the difference in acoustic properties might be detected and mapped using AVO techniques. In 2007 we are planning to collect a significant number of plug samples within the grainstone body of cycle 7 to characterize differences in petrophysical and acoustic properties of the two different pore types present in these grainstones. We will then measure elastic properties of these rock samples in the laboratory (in collaboration with either Jon Holder from the Department of Petroleum Engineering Sciences at UT or the Petrophysical Laboratory of University of Miami). In collaboration with Diana Sava (BEG), we will investigate the robustness of a current rock physics model for explaining the elastic properties of these rocks. On the basis of both a robust rock physics model and laboratory measurement, we will then expand our previous AVO study. The goal is to evaluate the feasibility of developing a prestack seismic detection and characterization workflow for separate vugs. Once the workflow is validated on synthetic data, we will ultimately try to apply it to a subsurface data set. For that purpose, we would like to ask help from our sponsors to locate and obtain a subsurface data set that contains reservoir rocks with both interparticle and separate-vug porosity. In conjunction with the flow-modeling study of Lawyer Canyon, we will begin to investigate the sensitivity of 4D seismic in such a system by calculating at various times a series of 3D synthetic seismograms from the fluid-flow model prediction. Doing so, however, will require that we have a robust rock physics model that can describe, under various degrees of fluid saturation, the elastic behavior of various rocks present in the model. 8

10 Outcrop Studies of Carbonate Heterogeneity Styles Platform, Slope, and Basin Two main areas of outcrop research are targeted for continued development of our understanding of carbonate slope and slope-to-basin transitions. The Shumard Canyon area and a new area in the Albian of the Fort Stockton Basin will be the focus of slope research. Shelf cycles in carbonates dominate production from carbonate reservoirs and have been at the center of RCRL research since its inception. We are considering two new areas, the Permian Khuff platform-top cycles exposed in Jebel Aktar in Oman and the Cretaceous-Tertiary carbonates of Libya. Both areas have exceptional outcrop of transitional to greenhouse carbonate-shelf cycles and are of keen interest as outcrop analogs to producing horizons in these regions. Shumard Canyon and the Platform Margins of the Guadalupe Mountains Carbonate-platform margins are one of the more complex reservoir settings in terms of primary porosity distribution and flow-unit structure. Carbonate-ramp systems are relatively systematic and have been extensively studied. Similarly, reef-rimmed margins, although not totally understood in terms of processes and architecture, have been examined in detail. A wide spectrum of carbonate margins exist between the ramp and rimmed-shelf end members, and although they contain significant hydrocarbon accumulations, they have received less intense study. The Victorio Peak to Bone Spring transition along the Western Escarpment is an impressive 500-m-thick exposure of a shelf-to-basin transition in a moderately steep profile that cannot easily be characterized as a ramp (depositional dips are between 10 and 25 ) or a rimmed shelf (no well-defined margin facies tract or debris-flow upper slope). The focus of research here is to evaluate the nature of the shelf-to-basin transition, to map the distribution of grain-rich reservoir facies, and to understand the relative role of traction deposition, sediment gravity flows, and mass-transport processes and slumps in prograding carbonate margins. Reconnaissance mapping and section measuring, coupled with lidar imaging, was begun in 2006 and will serve as the basis for an expanded effort in 2007, with continued mapping and modeling downslope into the Williams Gulch and Bone Canyon areas. 9

11 Airborne Lidar Model of the Southern Guadalupe Mountains At what scale do large platform-margin collapse scars or reentrants influence slope and basin accumulation of reservoir-quality carbonate fan-channel complexes? What large-scale structures control the character of platform-margin and slope accumulations, their fracture patterns, and their compaction-driven geometries? We believe that a 3D analysis of the Capitan shelf-to-slope system as exposed in the Guadalupe Mountain National Park is ideal for addressing issues related to large-scale stratal architectures of carbonate platforms. An airborne lidar survey will be carried out with a helicopter-mounted unit shooting at a low or oblique angle, allowing effective capture of cliff faces and flatter surfaces. This method was used successfully to collect lidar data from the Franklin Mountains in the fall of Airborne data collected in this way from the Guadalupe Mountains will allow us to work in digital 3D structure and stratigraphy at the platform scale, rather than at the flow-unit to local platform-margin scale associated with most of our models constructed using ground-based lidar. We will take bids over a range of coverage areas of varying size during the winter and will evaluate feasibility on the basis of cost and data density. Funding will come from Kerans startup funds, RCRL, and possible additional company input. I-10 Ft. Stockton Embayment Ramp to Basin Profile The RCRL is currently working on a variety of slope-to-basin deposits associated with different platform morphologies, such as steep margins of the Capitan (Playton) and moderate slopes of the prograding shelf of Last Chance Canyon (Ryan Phelps and Sam Scott), Victorio Peak, and Bone Spring Formation in Victorio and Shumard Canyons. In 2007 we would like to start investigating a low-angle slope-to-basin profile formed along the eastern flank of the Fort Stockton embayment. The uppermost Albian (Cretaceous) succession outcropping along the I-10 corridor from Ozona to Bakersfield (Texas) shows an almost continuous section from the ramp crest to the intrashelf basin with an undisturbed, exhumed Cretaceous paleobathymetry. We plan to capture data on the shape of the profile using available DEM data that, although low resolution, should be sufficient to capture the lowgradient slope involved. We will then visit representative roadcuts and outcrops along the profile, from the shelf to the basin, collecting samples to investigate not only the facies architecture but also the diagenetic changes observed along the profile. One of the unique aspects 10

12 of this profile is the superb exposures of the rudist rim and basinal equivalents, which contain both mud-rich and grain-rich reservoir-quality facies. Subsurface Reservoir Models and Modeling Methods In past years the RCRL has developed a systematic method for integrating high-resolution sequence stratigraphy, rock fabrics, core data, well log data, geostatistics, and scaleup approximations to produce superior 3D models of petrophysical stratification common in shallow-water platform carbonate reservoirs. These methods were demonstrated in the construction of a model for a one-square-mile area of the South Wasson Clear Fork reservoir in West Texas. We believe that these model construction methods can be adapted to improve 3D petrophysical modeling of any stratified carbonate system, and we are actively seeking opportunities to test the methods in other reservoirs, particularly Cretaceous examples. Because of the small size of the South Wasson Clear Fork model, only moderate lateral petrophysical trends were encountered. Therefore, in 2007 we plan to test our petrophysical model construction methods in a larger reservoir having more significant lateral petrophysical trends and to include seismic methods for filling the interwell volume. Fullerton Clear Fork Reservoir Model We have selected the Fullerton Clear Fork reservoir in West Texas because of its size (55 square miles), existing high-resolution sequence stratigraphic and petrophysical framework, and existing database of core data (25 wells) and quality-controlled well logs (850 wells). The BEG has recently completed a detailed geological and petrophysical model of this reservoir. Our approach will be to test our more advanced methods of distributing properties within the existing stratigraphic framework by using petrophysical properties calculated from wireline logs employing the rock-fabric method. Lawyer Canyon Outcrop Fluid-Flow Model The Lawyer Canyon San Andres outcrop on the Algerita Escarpment in the Guadalupe Mountains of southeastern New Mexico is a classic field site for sequence stratigraphy, spatial variability, and fluid-flow effects of petrophysical properties in a Permian dolomitized carbonate 11

13 ramp. Some the earliest RCRL work on sequence stratigraphy and rock-fabric methods were conducted on that outcrop. Many of our fundamental insights of the analysis and modeling of spatial variability were derived from petrophysical data collected there. Some of our most fundamental conclusions on fluid flow and scaleup were developed from 2D models of the outcrop. More recently lidar data from the Lawyer Canyon outcrop were used to construct a 3D geological model. In 2007, to complete our documentation of this classic outcrop, we plan to further develop this 3D model into a gridded porosity and permeability model for 3D fluid-flow simulation. Capillary Pressure Modeling of Initial Water Saturation To estimate the volume of remaining oil as a target for advanced recovery methods, the original volume of oil and gas in a reservoir is commonly compared with the produced oil and gas. Wireline logs are the principle source of saturation data used to make this estimate. In reservoirs where wireline logs are inadequate, however, mercury capillary pressure saturation models are commonly invoked to model initial water and hydrocarbon saturations. The common method is to normalize capillary pressure data using permeability-porosity ratios. The RCRL method is to normalize capillary pressure data on rock fabrics. In the past we have generated rock-fabricspecific models for initial water saturation on the basis of porosity and capillary pressure (reservoir height) but have been unable to produce a general equation that relates initial saturation to reservoir height, porosity, and rock-fabric number. However, we now have new capillary pressure data and thin-section descriptions, and in 2007 we plan to develop a general rock-fabric capillary pressure model using this augmented data set. Predictive Dolostone and Limestone Diagenetic Studies Predicting diagenesis is a complicated task that involves (1) identifying the diagenetic process, (2) modeling the hydrology and chemistry of the diagenetic fluid, and (3) relating the diagenetic product to the physical and chemical character of the original sediment and depositional environment. Historically the RCRL has not focused on diagenetic studies. In the past several years, however, we have supported student theses investigating dolomitization processes. In 12

14 2007 we plan to continue student support in this area and to initiate an investigation into burial diagenesis of limestones. Predictive Diagenetic Modeling of the Dolomitization Process For the past several years the RCRL has supported student research on modeling dolomitization by hypersaline reflux. Initial research focused on modeling dolomitization of a single highfrequency cycle. Current research focuses on modeling dolomitization of the extensive San Andres (Permian) outcrop located on the Algerita Escarpment, Guadalupe Mountains, New Mexico. The outcrop, 1,500 ft high and more than 30 miles long, has an equivalent subsurface section some 50 miles downdip and along depositional strike. Initial results were presented at the last annual meeting and include limestone-dolostone mapping, enlarging the stratigraphic model, and construction of the subsurface cross section showing distribution of anhydrite beds in the upper part of the formation. In 2007 we plan to focus on modeling the paleohydrology using hypersaline reflux dolomitization concepts. Burial Dissolution of Limestone for Creating and Modifying Carbonate Pore Space The loss of porosity during burial of limestone sediments is a well-known fact. Pore space is modified during this process, with pore space being both destroyed by compaction and cementation and created by mineralogical stabilization and grain crushing. The overall trend, however, is for porosity to be reduced with burial. Some geologists have concluded that porosity can be increased at depth by hydrothermal dissolution. In 2007 we plan to investigate the evidence for porosity increases related to burial diagenesis of limestones and to initiate a study of a limestone reservoir where porosity is thought to have been increased rather than lost due to burial processes. Database For 17 years the RCRL has been describing, interpreting, and modeling carbonate strata and petrophysical properties at the reservoir scale and, to a lesser extent, at the exploration scale. During this time, a range of data have been collected, including outcrop measured sections, core descriptions, petrophysical data, and complex 3D geological, petrophysical, and simulation 13

15 models. We have begun compiling and making available some of this data in the form of databases populated with tables and images. All data are referenced to a geographic area, geologic time, and, where applicable, latitude and longitude location. A visual search engine is also under development through a collaboration between Statoil and the RCRL to make data extraction from the database as easy as possible. Subscribing companies can access the database using Internet Explorer. Each company has a unique user account and password to insure access only to sponsors. Population of the database will continue in Data types currently loaded on the website include lidar models, Gocad models, LAS log and measured-section files, core descriptions, facies photos and photomicrographs, porosity and permeability data, stratigraphic sections, and maps. Data we intend to add this year include posters and presentations from research staff and students, field-trip guidebooks, and additional digital field studies. 14

16 List of 2006 Sponsors Anadarko Aramco BP Chevron ConocoPhillips ENI ExxonMobil Great Western Drilling Kinder Morgan Marathon Norsk Hydro Oxy Permian PDO Pioneer Shell Statoil 15