An Operation Geologist’s Venture into the Land of Geochemistry: Using Mud Gas Isotopes and Standard Geochemical Analyses to Identify Seals, Source Rocks, Gas Families, and Prospect Fairways in the Uinta Basin

Grau, Anne¹, Janell D. Edman², and Michael Dolan^3
1EOG Resources Inc, Denver, CO
²Geochemical Consultant, Denver, CO
³Dolan Integration Group, Louisville, CO

     The objective of this talk is to discuss methods of applied geochemistry that can be used by the average desk geologist to help characterize and understand petroleum systems in a practical scope that is useful to field characterization, development, and exploration. Using a case study and real data obtained in the Greater Natural Buttes Field of the Uinta Basin, several analytical techniques and interpretive methods will be presented that allow for a working geochemical model to be developed. Standard geochemical analyses such as measured vitrinite reflectance, thermal alteration index (TAI), and Rock-Eval ™ pyrolysis helped to characterize basin-wide maturity indicators and source rock quality. Mud Gas Isotope Analysis (MGIA), a technique that allows sampling of the mud stream gases while drilling, measures many components of gas chemistry including stable carbon isotopes of methane, propane, and ethane. Simple graphing techniques using MGIA data allows many useful interpretations including identifying gas “families”, observing seals, and providing evidence for migrated thermogenic gas accumulations. Specialized analyses, including Compound Specific Isotopic Analysis, helped to determine the association of gas and liquid hydrocarbons produced in a developing field. A variety of geochemical analyses, combined with guidance from a host of expert geochemists, resulted in the ability to identify important elements of the petroleum systems at Natural Buttes Field. Integration with other types of geologic characterization have allowed for better understanding of existing fields and exploration prospect fairways in the Uinta Basin.

AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah