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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
2004. The American Association of Petroleum Geologists. All rights reserved.
Strontium isotopic signatures of oil-field waters: Applications for reservoir characterization
Roger J. Barnaby,1 Gregg C. Oetting,2 Guoqiu Gao3
1Louisiana Geological Survey, Louisiana State University, Baton Rouge, Louisiana 70803
2Air and Liquid Advisors LLC, 12727 Featherwood Suite 108, Houston, Texas 77034
3P.O. Box 4778, Houston, Texas 77210
AUTHORS
Roger Barnaby has conducted stratigraphic studies of carbonates and siliciclastics in outcrop and subsurface for 15 years. He holds a Ph.D. from Virginia Polytechnic Institute and a B.S. degree from East Carolina University. Barnaby has worked on sedimentary successions of the Gulf Coast, Permian basin, Alaska North Slope, Middle East, and Caspian region. He maintains interests in carbonate diagenesis and geochemistry.
Gregg Oetting received an M.A. degree in geology in 1995 from the University of Texas at Austin. He is the author of six publications concerning geochemical and strontium isotopic variations in Edwards aquifer groundwaters. For the past seven years, Oetting has traded energy futures for leading merchant energy concerns. He works for an independent consulting business in Houston, Texas.
Guoqiu Gao received his B.S and M.S. degrees in geology from Central-South University, Hunan, China, and his Ph.D. in geology from the University of Texas at Austin. He works for a major oil company in Houston, Texas. His current interests lie in the field of geoscience computing.
ACKNOWLEDGMENTS
This investigation was conducted while the authors were affiliated with the Bureau of Economic Geology at the University of Texas at Austin. W. M. Fitchen assisted with geological interpretations and collecting water samples. J. V. White assisted with geological interpretations. J. Grubb helped collect water samples and constructed the geological database. S. C. Ruppel helped obtain financial support, contributed to the ideas, and reviewed the manuscript. A. R. Dutton reviewed the manuscript. AAPG reviewers Q. Fisher, B. Hitchon, and P.K. Mukhopadhyay helped improve the manuscript; we also appreciate comments from AAPG editor J. Lorenz. This research was funded by the Advanced Technology Program of the Texas Higher Education Coordinating Board, Project Number 003558-109.
This work would not have been possible with out the assistance and insights generously provided by individuals from the oil companies that operate Indian Basin and Dagger Draw fields. N. F. Hurley suggested Indian Basin and Dagger Draw fields for this study. We thank P. McWorter and D. Fly from Yates Petroleum Corporation; W. DeMis, K. Miller, J. Chapman, L. Brinton, and M. Woody from Marathon Oil Company; W. Hardy from Conoco; and D. Rit tersbacher from Chevron. S. Tweedy conducted the elemental analysis at the Mineral Studies Laboratory of the Bureau of Economic Geology at the University of Texas at Austin. R. S. Fisher assisted in use of SOLMINEQ.88 for solubility modeling.
ABSTRACT
The 87Sr/86Sr compositions of formation waters that were collected from 71 wells producing from a Pennsylvanian carbonate reservoir in New Mexico display a well-defined distribution, with radiogenic waters (up to 0.710129) at the updip western part of the reservoir, grading downdip to less radiogenic waters (as low as 0.708903) to the east. Salinity (2800–50,000 mg/L) displays a parallel trend; saline waters to the west pass downdip to brackish waters.
Elemental and isotopic data indicate that the waters originated as meteoric precipitation and acquired their salinity and radiogenic 87Sr through dissolution of Upper Permian evaporites. These meteoric-derived waters descended, perhaps along deeply penetrating faults, driven by gravity and density, to depths of more than 7000 ft (2100 m). The 87Sr/86Sr and salinity trends record influx of these waters along the western field margin and downdip flow across the field, consistent with the strong water drive, potentiometric gradient, and tilted gas-oil-water contacts.
The formation water 87Sr/86Sr composition can be useful to evaluate subsurface flow and reservoir behavior, especially in immature fields with scarce pressure and production data. In mature reservoirs, Sr isotopes can be used to differentiate original formation water from injected water for waterflood surveillance. Strontium isotopes thus provide a valuable tool for both static and dynamic reservoir characterization in conjunction with conventional studies using seismic, log, core, engineering, and production data.
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