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Abstract
DOI:10.1306/13341537St633525
Integration of Rock Fabrics and Stratigraphy for
Petrophysical
Quantification of Reservoir Framework


Rebecca R. Harrington,1 F. Jerry Lucia2
1Bureau of Economic Geology, The University of Texas at Austin, Austin, Texas, U.S.A.; Present address: XTO Energy, Fort Worth, Texas, U.S.A.
2Bureau of Economic Geology, The University of Texas at Austin, Austin, Texas, U.S.A.
ACKNOWLEDGEMENTS
This research was funded by ExxonMobil Production Company, The University of Texas System, and the U.S. Department of Energy under contract DE-FC26-01BC15351. ExxonMobil provided a comprehensive data set from the field
and access to cores and two-dimensional seismic data. David Smith and Terry Anthony served as invaluable project liaisons. Oxy U.S.A., Inc., also provided logs, data, and access to three-dimensional seismic data and cores. We thank Craig Kemp for his assistance in data transfer. Stephen Ruppel and James Gibeaut provided helpful critical reviews that improved the manuscript immeasurably. Lana Dieterich edited the manuscript. The illustrations were prepared with the assistance of the graphics group at the Bureau of Economic Geology (BEG). The support of this research by the Landmark Graphics Corporation via the Landmark University Grant Program is acknowledged. The publication was authorized by the director of BEG.
ABSTRACT
A major task in building a reservoir model is quantifying the geologic framework using petrophysical
properties. Porosity and water saturation values can be obtained from wireline logs, but permeability is a rock property that cannot be obtained directly from logs. Commonly, a single porosity-permeability transform is used to estimate permeability from porosity logs. However, such an approach fails to account for variations in porosity-permeability relationships that are common in carbonates. In this study, rock-fabric-specific porosity-permeability transforms are used together with log porosity to calculate permeability. Although the reservoir at Fullerton
field
contains several rock fabrics, they can all be grouped into three
petrophysical
groups, each having a unique porosity-permeability relationship. These
petrophysical
groups can be linked to facies and stratigraphy using an integrated study of thin sections and cores.
The lowermost stratigraphic unit in the reservoir (the Wichita of sequences L1 and L2) is composed dominantly of peritidal facies consisting of fine-crystalline mud-dominated dolostones and mud-dominated limestones, all of which can be assigned to a single petrophysical
group (class 3). In contrast, rocks of the overlying Lower Clear Fork (sequences L2.1–L2.3) display far more
petrophysical
variability, both stratigraphically and geographically. Sequence L2.1 comprises an upper late highstand peritidal succession and a lower, transgressive, and early highstand systems tract succession of subtidal facies. The peritidal rocks such as those of the Wichita are fine-crystalline mud-dominated fabrics of
petrophysical
class 3. The subtidal rocks, which contain both limestone and dolostone, are more variable. Dolostones are mostly medium-crystalline, subtidal grain-dominated dolopackstones and medium-crystalline, mud-dominated
petrophysical
class 2 rocks. Limestones are composed of oomoldic grainstone. Although grainstones normally possess
petrophysical
class 1 rock fabrics, they display class 2
petrophysical
relationships because they are moldic. Lower Clear Fork sequence L2.2 is also dominated by class 2 medium-crystalline dolostone fabrics. However, these rocks display class 1 porosity-permeability relationships because of abundant poikilotopic anhydrite. Oomoldic limestone, such as that in sequence L2.1, is also locally common. The uppermost L2.3 reservoir sequence contains fine-crystalline dolostone, class 3 peritidal facies.
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