Research Plans for 2003
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). 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.
The RCRL program has run continuously since 1987 and has produced more than 30 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 Website (www.beg.utexas.edu/indassoc/rcrl/index.htm). Highlights for the year include Charles Kerans' International AAPG Distinguished Lecture Tour, Jim Jennings' selection by Shell International for a 1-year sabbatical in Shell's research laboratory at Rijswijk, the Netherlands, Lucia and Jennings' presentation of a reservoir-modeling workshop with an engineering focus.
RCRL has maintained a membership of between 13 and 18 companies per year (see section on funding for list of 2002 sponsors). The sponsorship currently has strong interests in Permian and Alberta Basins, as well as Middle Eastern carbonate reservoirs. This enrollment, supplemented by government grants, supports between three and six professional staff members and varying numbers of graduate student research associates, plus strong computer, editing, and graphics support.
Two geologists, a geological engineer, and a reservoir engineer/modeler form our core group:
Dr. Charles Kerans, Geologist
Mr. Jerome A. Bellian, Geologist
Mr. F. Jerry Lucia, Geological Engineer
Dr. James W. Jennings, Jr., Reservoir Engineer/Modeler (on sabbatical)
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 student staff, which has included several award-winning students, many of whom are now working in the industry.
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 2003 include
Enlarging the rock-fabric/petrophysical database and making outcrop and subsurface studies available from an FTP site.
Continuing to develop methods of creating 3-D outcrop images using a state-of-the-art digital outcrop-surveying tool called ILRIS 3D. Plans include integrating petrophysical and seismic outcrop data at Victorio Canyon into the ILRIS model and constructing a 3-D reservoir model of the rudist reef complex at Pipe Creek.
Constructing a reservoir model for the Cogdell Canyon Unit as part of our subsurface studies. This field is an active CO2 flood in an icehouse, isolated-platform setting and is a continuation of our investigation into the similarities and differences between icehouse and greenhouse carbonate reservoirs. In addition, we will be involved in the study of Fullerton field, West Texas, which is being funded by DOE, University Lands, and Exxon/Mobil.
Enlarging our investigation into characterizing the geology and petrophysics of touching-vug pore geometries. We continue to collect large outcrop samples and perform flow-simulation studies using high-resolution CT scans of the touching-vug pore system. A new project is to construct a flow simulation of a well-constrained, 3-D outcrop model of a karst system. In addition, we plan to expand the Sacroc and Cogdell studies to include well history as a means of locating production from vuggy intervals.
Developing methods, using high-resolution CT scans, to more accurately characterize the rock fabric and pore structure of carbonate samples, and then using these methods to characterize relative permeability data from 30 Permian samples.
Continuing the RCRL mentoring program by working with Kinder Morgan and Oxy Permian on characterization of the Sacroc and Cogdell reservoir complexes.
If you have any 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).
With this proposal, we invite you to participate in the continuation of the RCRL Carbonate Reservoirs Research Program. A list of sponsors during 2002 can be found at the end of this proposal. In 2003 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 Website.

Research Directions for 2003

Carbonate Reservoir Database

In 2002 we distributed an initial copy of our rock-fabric/petrophysical database containing photomicrographs, rock-fabric descriptions, and petrophysical data from 156 samples selected from 8 carbonate reservoirs and 1 outcrop. In 2003 we plan to increase the number of samples and reservoirs. In addition, we plan to enlarge the database to include slab photographs, reservoir models, and typical wireline logs.
Quantitative geology is becoming more important as exploration and production questions become more complex. The RCRL has extensive outcrop-analog datasets that can be useful for providing answers to these complex questions. In 2001 and 2002 a series of digital geologic materials were assembled for the Pecos, Apache Canyon, and Victorio Canyon areas, and digital core-image datasets were compiled for several Shuaiba subsurface studies. In addition, our first geological model built in Gocad for Victorio Canyon, West Texas, was completed. In 2003 we plan to make these datasets available from an RCRL archive site accessible on the web.
3-D Outcrop Modeling
In 2002 RCRL researched, tested, and purchased a state-of-the-art, digital, outcrop-surveying tool called ILRIS 3D. We now have the capability of acquiring 5-cm point-spaced data from outcrop faces as much as 1 km distant. The original code was written for civil engineering, but we have already rewritten most of the code needed to process and manipulate outcrop data. ILRIS data have served as the basis for a method of constructing realistic 3-D reservoir models using a series of interpretation techniques similar to those used for interpreting horizons in a seismic dataset. These horizons are then exported to a geocellular-mapping package. We plan to build on and refine this approach in 2003 by
Developing the use of spectral data in conjunction with laser-intensity data in order to classify multiple components in a way that will highlight geological attributes. Combining spectral and petrophysical data will lead to robust outcrop analogs that can be more readily and confidently applied to subsurface problems.
Petrophysically quantifying the Victorio Canyon slope/basin floor 3-D model as an essential step in constructing a realistic 3-D property model for this dataset. We plan to collect a combination of velocity, porosity, and permeability data from the outcrop using an approach that is tied to our ILRIS model, allowing us to investigate links between parameters such as impedance, porosity, and slope weathering profile. Our desire is to find fast and efficient ways to maximize the XYZI (I=intensity) data for generating high-resolution seismic images, as well as Phi/K data for property modeling. The Victorio Canyon dataset is the logical place to begin because we are the farthest along on this model and a range of rock fabrics and properties already exist. Forward seismic modeling and fluid-flow simulation are possible activities for this dataset.
Completing the Pipe Creek rudist-buildup dataset through detailed geological mapping by linking RTK GPS to the ILRIS dataset. In 2002 we constructed an initial model of the creek bed, but we now need to carry out a more detailed geologic characterization of the outcrop facies. Using detailed surface maps and data gathered from core material, we will construct a geocellular model. In addition, ground-penetrating radar may be tried here to improve imaging of isolated caprinid rudist geometries.
Evaluating several new areas for applying the ILRIS tool for reservoir-scale geologic mapping. We are considering previously studied datasets in the Permian of the Guadalupe Mountains, the Pennsylvanian of the Sacramento Mountains, and the Cretaceous of the Pecos River Canyon. We are also in discussion with several sponsor companies regarding areas that are of mutual interest, as well as areas that might be of specific interest to a single company, in which we might design a project with a single company in mind. We are particularly interested in suggestions from sponsor companies in this area.
Subsurface-Oriented Integrated Studies
Cogdell Unit (Pennsylvanian)
A special mentor study for RCRL during 2003 will include construction of a reservoir model for the Cogdell Canyon Unit. This field is an active CO2 flood in an icehouse, isolated-platform setting. The Cogdell study has many similarities to the recently completed Sacroc study and is thus to some extent a review of best practices. However, we have already noted a substantially different architectural style at Cogdell that involves extensive erosion. Karst development at several sequence boundaries adds to the complexity of this reservoir. Cogdell has an excellent database of 3-D seismic data, multiple cored wells, a relatively modern log suite, and excellent dynamic data that will form a critical element of RCRL's research on touching-vug pore geometries.
Fullerton Lower Clear Fork Field (Permian)
RCRL will be involved in constructing a reservoir model of Fullerton Lower Clear Fork field in conjunction with an integrated team of geologists, geophysicists, and engineers funded principally by Exxon/Mobil, University Lands, and the U.S. Department of Energy. This study is partly a test of methods developed by RCRL for building a carbonate reservoir model.
Rock-Fabric, Petrophysical Studies
Touching-Vug Research
The most difficult problem in predicting performance in a carbonate reservoir is modeling touching-vug pore geometries, including fractures, solution-enlarged fractures, collapse breccias, caverns, and microfractures. Touching vugs have a variety of origins and occur as a karst overprint, microfractures formed during burial compaction and selective dissolution, and tectonic fractures formed by regional tectonic stresses. We have completed several field studies that include information on patterns of microfractures related to burial compaction and selective dissolution. The impact of these microfractures on petrophysical properties, namely permeability, can be characterized from core data because the pore sizes are smaller than core sizes. Current data suggest that permeability is enhanced five- to tenfold over matrix permeability. Defining the petrophysics and distribution of large touching-vug systems, such as those associated with karst processes, is more difficult because the pore systems are generally much larger than core samples. We have considerable information on karst processes and associated patterns of touching vugs from outcrop studies but little information on the permeability of these large systems. Our research has focused on gathering petrophysical and production information from well-studied outcrops and reservoirs in order to improve methods of characterizing fluid flow in large-pore systems.
Our approach is to integrate outcrop and subsurface studies. In collaboration with Richard Ketcham of the Department of Geological Sciences and Steven Bryant of the Petroleum Engineering Department, we have an ongoing project collecting large outcrop samples and performing flow-simulation studies using high-resolution CT scans of the touching-vug pore system. We encountered a major problem in defining flow in large pores because Darcy's Law for flow in porous media did not apply. We are currently developing a method of integrating Stokes' Law for flow in large pipes with Darcy's Law. The samples being used are from a well-known Cretaceous rudist reef complex in Central Texas that, as part of our imaging research, is being mapped by using ILRIS. This outcrop is thought to be an analog for Cretaceous rudist reservoirs in the Middle East.
A highly karsted Lower Ordovician outcrop in Central Texas has been described in 3-D by Robert Loucks and others using outcrop, cores, and ground-penetrating radar. This work has provided us with an opportunity to construct a detailed 3-D flow-simulation model of a karsted reservoir. Porosity and permeability values are available from the core data and will be used initially to populate the geologic model. In addition, we plan to gather outcrop samples for high-resolution CT scan and flow-simulation experiments to obtain a better estimate of flow properties in the touching-vug pore system. This outcrop is an analog of many Ellenburger reservoirs in the Permian Basin, U.S.A., as well other highly karsted reservoirs.
We are currently studying two Pennsylvanian limestone reservoirs in the Horseshoe Atoll complex, West Texas, the Sacroc and Cogdale reservoirs. These reservoirs have undergone extensive meteoric diagenesis and show evidence of karsting and development of touching-vug pore systems. To date, however, we have modeled only matrix permeability, and our attempts to use core data to characterize flow in the touching vugs have had limited success. We plan to expand this study to include well history as a means of locating production from vuggy intervals. We will do so by searching for permeable intervals that cannot be explained by matrix permeability. We will use injection profiles, sequential gamma-ray logs, and interval tests to locate zones where flow is occurring. We also plan to investigate using acoustic logs for locating touching vugs.
Quantification of Heterogeneity at the Core-Plug Scale
Understanding the flow properties (permeability and relative permeability) of core samples has always been hampered by inadequate characterization of pore-size distribution. Studies have demonstrated that quantitative measurements of pore types from thin sections are often biased because of their small volume relative to the core sample. High-resolution CT scans of the pore network are now available through the CT facility in the Department of Geological Sciences. We have scanned 50 samples from the South Wasson Clear Fork reservoir and have obtained relative-permeability data from 30 samples. In 2003 we plan to use this dataset to develop methods of characterizing the rock fabric and pore structure of carbonate samples more accurately.
Mentoring Projects
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. Several activities are planned for work between RCRL and sponsors for 2003. Sponsors are encouraged to contact us with projects that could be mutually beneficial.
List of 2002 Sponsors
Amerada Hess
Great Western Drilling
Kinder Morgan

Occidental Petroleum
Petroleum Development Oman
Shell International

Updated March 2010