Research Plans for 2005
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), 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 3D reservoir environment.
The RCRL program has run continuously since 1987 and has produced more than 45 external publications, as well as BEG publications, on carbonate reservoir characterization, sequence stratigraphy, petrophysics, geostatistics, and petroleum engineering. We provide research results to our sponsor companies through annual review meetings, CD’s, preprints of publications, short courses on geologic and engineering aspects of our research, and a mentoring program in which we work hands-on with industry staff using their datasets. In addition, our results are posted in a password-protected part of our Web site: www.beg.utexas.edu/indassoc/rcrl/index.htm.
RCRL has maintained a membership of between 13 and 18 companies per year (see list of 2004 sponsors at end of proposal). The sponsorship currently has strong interests in a range of domestic and international carbonate reservoirs ranging in age from Ordovician to Tertiary. This enrollment, supplemented by other grants, supports between three and six professional staff and varying numbers of graduate student research assistants, plus strong computer, editing, and graphics services.

Principal Staff

Dr. Charles Kerans, Geologist, Principal Investigator
Mr. F. Jerry Lucia, Geological Engineer, Principle Investigator
Dr. Xavier Janson, Geologist
Mr. Jerome A. Bellian, Geologist
Associate Staff
Dr. James W. Jennings, Jr., Reservoir Engineer/Modeler
Dr. Fred Wang, Petroleum Engineer
Dr. Hongliu Zeng, Geophysicist
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. We are also very proud of our graduate students, several of whom have won awards and many of whom are now working in the industry.
If you have questions on any aspects of the RCRL Carbonate Reservoirs Research Program, please contact Charlie Kerans (512-471-1368 or charles.kerans@beg.utexas.edu) or Jerry Lucia (512-471-7367 or jerry.lucia@beg.utexas.edu).
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 2005 are focused on the following areas:
Primary areas of research
Retrievable compilation of carbonate reservoir architecture and petrophysical quantification.
Geological and petrophysical characterization of vuggy porosity.
3D modeling of geologic facies and petrophysical rock-fabric elements using outcrop and subsurface data.
Additional areas of research
CT imaging for characterizing heterogeneity at the core-plug scale.
Diagenetic modeling of the dolomitization process.

Mentoring projects for sponsoring companies.

If you have any questions on any aspects of the RCRL program, please contact Charlie Kerans (512-471-1368 or charles.kerans@beg.utexas.edu) or Jerry Lucia (512-471-7367 or ).
With this proposal, we invite you to participate in the continuation of the RCRL Carbonate Reservoirs Research Program. A list of sponsors during 2004 can be found at the end of this proposal. In 2005 the annual RCRL Industrial Associates contribution to the program will continue to be $45,000 per year. Our industrial sponsors will continue to receive research results at annual review meetings, in short courses, during mentoring activities, in publications and CD’s, and on our Web site.

Research Directions for 2005

Synthesis and Compilation of Carbonate Reservoir Architecture and Petrophysical Quantification

The RCRL has been in the process of describing, interpreting, and modeling carbonate strata and petrophysical properties at the reservoir scale and to a lesser extent at the exploration scale for 16 years. During this time data have been collected that include everything from basic outcrop measured sections, core descriptions, and petrophysical data to complex 3D models, global transforms for porosity-permeability models, and reservoir flow simulations. We have begun the process of compiling and making some of these data available to sponsors in the form of databases with tabular and image data. This process has been hindered by the lack of a meaningful hierarchical organization and format with which to display the enormous amount of data we have collected over the past years with your support.

In 2005 we plan to change direction toward synthesizing all available data that we have into key topical areas and supplement these data with selected information from the literature. We envision that this will be a multiyear project starting in 2005 with a completion target of 2007. Progress will be reported at each yearly review meeting, and interim access to the results will be provided to the sponsors at that time. We anticipate that the data will reside on a server here at BEG with access password protected. In order to protect our current and future sponsors, we have decided that access to this database/synthesis product will be on a pay-as-you-go basis starting with the 2005 sponsorship fee. There will be a chargeback fee for those companies that join the RCRL in future years or that skip a year.

The modules have not yet been decided upon but will probably be based on geologic age because that is the simplest approach. Special topics such as facies dimensions carbonate petrophysics, etc., will be covered. The synthesis will include search engines to find specific items such as outcrops, reservoirs, lithology, and rock fabric, among other parameters. Each outcrop and reservoir will have a brief description of the geologic context, the basic data, and the interpretations presented. The basic data will include core descriptions, outcrop sections, core photos, petrophysical data, thin-section descriptions and photos, typical wireline logs, and capillary pressure. Interpreted data will include geologic maps and cross sections, 3D models, and reservoir models with brief write-ups of the interpretation methods used. This initial effort may evolve in several possible directions on the basis of sponsors’ input and our experience.

Geological and Petrophysical Characterization of Vuggy Porosity

Geological and petrophysical characterization of vuggy porosity as related to fluid flow and hydrocarbon recovery remains a critical problem in the construction of carbonate reservoir models for reservoir performance prediction. We have made considerable progress toward converting wireline logs into matrix permeability profiles and distributing these data within a sequence-stratigraphic model. Little progress, however, has been made toward quantifying the effect of vuggy porosity on recovery. Much of our understanding is confined to vugs that are connected only through the interparticle pore system called “separate vugs.” However, predicting the distribution of separate vugs remains a major concern. Vugs that form their own connected pore system, called “touching vugs,” are poorly understood. Touching-vug systems are formed by a complex combination of processes including dissolution, fracturing, cavern collapse, and regional tectonism. Touching-vug and interparticle porosity together form a bimodal pore system that is poorly understood and difficult to simulate.

Mapping, Characterizing, and Modeling of Bimodal, Touching-Vug Pore Systems

Touching-vug pore systems are commonly composed of both matrix and vuggy porosity. Whereas there are several adequate methods for characterizing matrix properties petrophysically using information gained at the core scale, touching vugs are normally composed of large vugs that cannot be adequately studied at the core scale. The scale at which large vugs are connected is a key issue for understanding the flow properties of touching vugs. Equally important is the method by which the vugs are connected. Over the past few years, the RCRL has developed a research program designed to investigate the geology and flow properties of bimodal touching-vug pore systems. This program has been focused on studying touching vugs at various scales using material from carbonate outcrops and production data from carbonate reservoirs.

The 1-ft scale has been studied using a large outcrop sample of rudist rudstone containing large rudist vugs and inter-rudist pore space. Todd Arbogast and coworkers at the UT Institute for Computational and Applied Mathematics have developed code for coupling Stokes flow for the vugs and Darcy flow for the matrix using a high-resolution CT scan of the outcrop sample. Efforts to characterize interconnections and model flow in this sample continue using a pore-space model based on a high-resolution CT scan. This project is funded by the RCRL and a National Science Foundation grant with Dr. Arbogast as principal investigator and will continue in 2005. As part of this project we plan to investigate flow at the 10-ft scale by drilling wells in the outcrop from which the large sample was taken. Two wells will be drilled 10 ft apart, air injected in one well, and pressure and flow rate measured in the other. This procedure should provide us with a measure of effective permeability at the 10-ft scale.

For the 100-ft scale, we have initiated a study of a karsted Cretaceous road cut that contain faults, fractures, solution-enlarged fractures, and caves. The objective of this activity is to build an explicit dual-porosity model showing the distribution of porosity in the fractures, dissolution porosity, and matrix porosity. This model will be used to experiment with flow properties at various scales. In 2004 a relationship between tectonic fractures, stratigraphy, matrix permeability, and dissolution at various scales was developed. In 2005 we hope to complete the construction of a 3D model showing the distribution of matrix and vuggy porosity suitable for flow simulation studies.

Franklin Mountain Karst Study

Caves and paleocaves (karst systems) are a significant player in the development of touching-vug pore systems. During the last two decades, studies from two divergent areas, oil exploration and development and cave hydrology and geochemistry, have improved our understanding of the processes of cave development and of paleocave systems. However, our ability to develop robust geologic models and to generate efficient and reliable resource predictions in these systems remains inadequate.

In 2005 we propose to focus on the characteristics and origins of paleocave complexes and associated pore systems found in the mega karst system exposed in the Ordovician outcrops, Franklin Mountains, El Paso, Texas. The research will document 3D geometric patterns of paleocave systems, identifying elements and processes that control the patterns and developing geochemical and geomechanical models for their origin. An important aspect of this research will be to develop methods for forward modeling of the diagenetic processes associated with cave formation.

Reservoir Study

At the reservoir scale, in 2004 we analyzed injection data from several wells and obtained permeability estimates from touching-vug intervals in the Cogdell Pennsylvanian field in the Permian Basin. In 2005 we plan to initiate a reservoir study of the Hobbs San Andres. Production data and core descriptions from the Hobbs San Andres (Permian) field strongly indicate the presence of karsting and touching-vug porosity. Numerous cores are available, and about half the 600 wells have good suites of wireline logs. The field is actively being converted to a CO2 flood, and modern production data are also available. We are confident that a detailed reservoir study of this reservoir will provide important insights into modeling and predicting performance of touching-vug pore systems.

Seismic Modeling of Separate-Vug Pore Space

In 2005 we plan to produce a 3D synthetic seismogram for the Lawyer Canyon model focused on imaging the moldic porosity that has been mapped in high-frequency cycle 7. In 2004 we showed that the velocity changes induced by vuggy grainstone compared with non-vuggy grainstone can generate a large enough impedance contrast to be detected on seismic images. In 2005 we plan to study the petromechanical characteristics of this vuggy grainstone by collecting numerous samples and measuring their mechanical, velocity, and petrophysical properties. The initial task will be to identify unique petromechanical characteristics of the vuggy grainstone that will allow us to unequivocally differentiate them from the nonvuggy grainstone. Our initial review of the petrophysical literature shows that vuggy grainstone might have a slightly different Vp/Vs ratio. We will try to investigate further petrophysical properties such as bulk and shear modulus or Poisson ratio. Eventually, we will use these mechanical characteristics to build an elastic impedance model that will be used to generate initially a 1D synthetic seismogram at various offset angles using a full elastic wave equation method. Ultimately, the AVO response of this vuggy grainstone will be analyzed.

3D Modeling of Carbonate Reservoir Analogs

The RCRL continues to be committed to extracting critical information on carbonate reservoir heterogeneity from key outcrops in order to understand scale and variability in three dimensions, most importantly in the lateral, interwell dimension. In the past we have focused on developing sequence-stratigraphic methods and detailed lateral petrophysical variability, mostly in two dimensions. With the advent of high-resolution ground-based lidar imaging technology we are able to accurately image outcrop data in three dimensions and provide 3D spatial statistics of various facies and geobodies. We have used this type of information in our study of the Poza Rica deep-water carbonate field in Mexico to construct a realistic geologic model and are confident that collecting 3D spatial statistics will provide our sponsors with tools to better construct geologic images.

In 2004 we collected lidar data in Lawyer Canyon (Permian) and Painted Canyon (Cretaceous), areas we have previously studied. In addition we initiated work on the Virgil (Penn.) algal mounds in the Sacramento Mountains, New Mexico, and the famous Windjana Gorge (Devonian) in Australia. In 2005 we plan to finish work on the Virgil mounds and initiate a project on the Mississippian crinoidal buildups in the Sacramento Mountains, continue supporting a graduate student studying the Windjana Gorge, and initiate a lidar study of the Permian shelf margin in Last Chance Canyon, Guadalupe Mountains. In addition we are supporting a Ph.D. thesis on slope carbonates that will continue through 2005.

Dry Canyon

In 2005, we will finish the geocellular model for Dry Canyon. Several regional surfaces as well as the stratigraphic grid remain to be built. The major challenge next year will be to populate the grid with realistic facies. Especially, the siliciclastic interval and the mixed siliciclastic and carbonate cycles will require some complex krigging extrapolation or some other extrapolation methods. We expect to test several different approaches to model the mound distribution as well as the facies distribution. In 2004 we used a stochastic approach to model the mound distribution in 3D. Next year, we will try both an object-based approach and a multipoint statistical method.

Alamo Canyon

The deeper water outer-ramp buildups of the Sacramento Mountains as described by Bachtel and Dorobek represent an excellent outcrop analog for the complex Upper Pennsylvanian Cisco mounds that cap the Horseshoe Atoll reservoirs at Sacroc and Cogdell. Because of the complex interplay of steep buildup depositional topography, syndepositional erosion, and sediment gravity flow processes, an actualistic model for stratigraphic architecture and porosity/permeability distribution at Sacroc and Cogdell has been difficult to develop. Although the Lake Valley is Mississippian and the Cisco is Upper Pennsylvanian, numerous similarities exist between these two occurrences. Most important is the deeper water, crinoidal mud-mound facies that predominates in both cases. Second is the interplay of steep buildup topography and sediment-gravity-flow processes. Significant differences between the examples other than age include the icehouse (Horseshoe Atoll) vs. transitional (Lake Valley) style of stratigraphy and the isolated atoll vs. land-attached ramp setting. While considering these differences, we see the excellent outcrop quality of the Lake Valley exposures, their direct application to addressing issues of stratigraphic modeling of the Horseshoe Atoll reservoirs, and the wider interest of complex outer-ramp to slope stratal geometries of this prograding outer-ramp/buildup setting to provide a valuable analog dataset.

The products we will generate for the Alamo Canyon area of the Lake Valley system include a full 3D geologic model for the 3 ? 4 km area of the canyon, including buildups, overlying prograding ramp grainstone lobes, and enough lateral control to capture the along-strike variability of the lobe to interlobe facies. The model will be built using lidar, photomosaic mapping, and section measuring, using available detailed mapping by Steve Bachtel of ExxonMobil. We will also construct a Gocad model of the system and attempt to populate this model with petrophysical properties from the Horseshoe Atoll data for use in seismic modeling.

Windjana Gorge

We are currently in the process of acquiring data for a 3D stratigraphic model of the Late Devonian Windjana Gorge outcrop. This area, located in Western Australia’s Canning Basin preserves arguably some of the world’s best examples of Paleozoic vertical escarpment platform margins. We hope to address two key issues here: (1) What is the spatial variability of depositional facies, stratal geometries, and sequence architecture associated with these vertical escarpment platform margins? (2) How does the observed change from aggradational to progradational platforms in Windjana Gorge affect fracture patterns in the reefal margin and marginal slope? The 3D model generated by this study will integrate lidar, detailed geologic mapping, section measurement, and existing conodont biostratigraphy. The results of this study will contribute to our understanding of the spatial complexity of platform margins.

Last Chance Canyon

The Last Chance Canyon area of the Guadalupe Mountains will serve as one of our key outcrop modeling areas for 2005. This work will be done by two graduate students as the basis of their Master of Science theses with completion scheduled for tfall 2006. Last Chance Canyon is well known to both the U.S. and international communities as one of the classic examples of sequence-stratigraphic architecture and has been the focus of several very detailed and thorough studies. Until recently, our understanding of the Last Chance Canyon geology has been limited to idealized 2D dip-oriented cross sections. With the newly developed 3D mapping and modeling technologies using lidar, we believe that we will be able to add substantially to our understanding of the nature of prograding systems in carbonates. We expect to observe the scales of continuity of individual clinoforms, the line- vs. point-source character of these clinoforms, and the interaction of deeper-water buildups on the distribution and source of down-slope sediments.

Slope Deposits

In 2005 we plan to continue our investigation into the geology and petrophysics of carbonate slope deposits by gaining access to several subsurface datasets from the Permian Basin that are analogous to the Permian toe-of-slope Victorio Canyon outcrop and by supporting a Ph.D. student studying well-known slope outcrops. The goal of the subsurface studies is to apply the knowledge gained from the Victorio Canyon outcrop to subsurface analogs. The main goal of the Ph.D. thesis is to produce general carbonate slope depositional models that identify key relationships linking large-scale geometrical observations to reservoir spatial heterogeneity. The data for this study will come from the Upper Devonian strata of the Canning Basin, northwest Australia, Middle Triassic strata of the Dolomites Alps, northern Italy, and possibly Upper Permian strata of the Delaware Basin, West Texas. Understanding of carbonate slope systems tract partitioning with respect to (1) failure/shedding mechanism, (2) facies types and distribution, (3) external geometry and internal architecture, (4) spatial sediment storage capacity, and (5) syn- to post-sedimentary diagenesis is critical for efficient hydrocarbon exploration and performance prediction in these settings.

Seismic Modeling

In 2005 we will continue to generate 3D synthetic seismograms for our different outcrop models. We are currently improving our modeling capabilities. We are planning to use a 3D exploding reflector method based on a one-way propagation of an acoustic wave. This algorithm has been developed at BEG by geophysicist Sergey Fomel. We will be able to produce more realistic synthetic volumes where we can analyze geometrical artifact, amplitude tuning, and the response of various seismic attributes, test inversion algorithm, and calculate volumetric error. We plan to produce 3D synthetic seismograms for the Dry Canyon, Painted Canyon, and Lawyer Canyon models.

Additional Areas of Research

Diagenetic Modeling of the Dolomitization Process

In 2004 we initiated work on diagenetic modeling by arranging for a graduate student to model a Cretaceous dolostone bed in a tidal-flat-capped high-frequency cycle where we can reasonably assume that the hypersaline reflux dolomitization model applies. The focus is on flow rate, which means that reasonable values of permeability at the time of dolomitization are critical. Initial results indicate that the 1-m-thick dolostone bed can be dolomitized in a few thousand years, which suggests that hypersaline conditions were short lived. We anticipate completion of this project in 2005 and plan to continue this investigation in areas where the dolostone is much thicker and contains multiple peritidal cycles.

Quantification of Internal Core-Plug Variability with CT Scanning

We continue to research methods of integrating rock-fabric descriptions and petrophysical properties. In the past we have relied on descriptions of thin sections made from plug-end pieces, which may not accurately represent the pore structure of the complete core plug. Quantification of the pore-size distribution within a core plug was initiated in 2004 by statistical analysis of 35 high-resolution CT scans. Preliminary results suggest that the standard deviation ratio is an indicator of average pore size. The standard deviation ratio will range from zero to one and should indicate the average pore size relative to the CT scan resolution. Smaller pores will produce more uniform gray images with smaller standard deviation ratios. Larger pores will have more variable CT images and larger standard deviation ratios. Thus, the standard deviation ratio might be an indicator of rock fabric that at least partially corrects for the interdependence of mean porosity and porosity variance. We plan to continue this research in 2005.

Mentoring and Projects within the RCRL Umbrella

Direct contact with the technical staff of our sponsoring companies is an important ongoing aspect of our program. This interaction allows us to test our concepts and methods on real problems while assisting sponsors in developing new reserves. In 2004 we did mentoring projects for Occidental Petroleum, Aramco, and Production Development Oman. In 2005 we are planning to have mentoring projects with Occidental Petroleum, Kinder Morgan, and Aramco. Sponsors are encouraged to contact us with projects that could be mutually beneficial.

List of 2004 Sponsors
Great Western Drilling
Kinder Morgan
Occidental Petroleum
Petroleum Development Oman
Shell International

Updated March 2010