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Multidisciplinary Thermal Maturity Studies Using Vitrinite Reflectance and Fluid Inclusion Microthermometry: A New Calibration of Old Techniques

¹ BP Amoco Corporation, 200 Westlake Park Boulevard, Houston, Texas 77079; tobinrc{at}bp.com
² Integrated Geodata Services, 13823 Purple Martin, Houston, Texas 77083; claxtonbl{at}msn.com

Rick Tobin is a senior geologist with BP Amoco's Upstream Technology Group in Houston, specializing in reservoir quality prediction. He received geology degrees from James Madison University (B.S., 1977) and the University of Cincinnati (M.S. 1980, Ph.D. 1982). His technical specialties and current research interests include sedimentology, sedimentary petrology, fluid inclusion microthermometry, and related thermal maturity technologies. Tobin is an active member of AAPG, SEPM, and Sigma Xi.Brenda Claxton has worked exclusively on integrating vitrinite reflectance data with other organic and inorganic thermal indices in a multidisciplinary technology team since beginning her career with Amoco in 1975. Her major focus has been to create a thermal and geochemical database to predict expulsion timing for basin modeling, in-reservoir increases of API gravity for product quality, and timing of reservoir destruction for exploration. She is a founding member of the Society for Organic Petrology.

A critical component of petroleum exploration risk assessment involves quantifying the risks associated with the presence of a viable hydrocarbon system. This requires an accurate estimate of thermal maturity and thermal history. However, in some sedimentary basins, traditional organic-based maturity tools such as vitrinite reflectance cannot be used because of various geologic and sampling limitations. This article establishes fluid inclusion microthermometry as a new inorganic thermal maturity tool that can be used to help fill the void in these situations. This tool uses an empirical calibration of fluid inclusion data and vitrinite reflectance data to estimate thermal maturity.

Our empirical approach uses rigorous sample selection criteria that improve the statistical chance of analyzing aqueous fluid inclusions that have been thermally reequilibrated (stretched). This empirical calibration is based on a worldwide set of data that yield a logarithmic correlation having r² = 0.96 for an ideal sample set and r² = 0.81 for a nonideal sample set. The amount of data scatter (absolute deviation of measured vitrinite reflectance in % R_o) from the logarithmic correlation line is minimal (±0.12% R_o for the ideal data set). This new calibration, along with the sample selection and data analysis procedures described in this study, forms the basis for a new thermal maturity technique.