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).
Funding
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
1.
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.
2.
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.
3.
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.
4.
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
Anadarko
Aramco
BP
Chevron/Texaco
ExxonMobil
Great Western Drilling
Kinder Morgan
Marathon
Occidental Petroleum
PanCanadian
Petroleum Development Oman
Shell International
Statoil
TOTALFinaElf
