Geochemical Characterization of Solid Bitumen Deposited
within the Mississippian Sandstone Reservoir of the Hitch Field, Southwest
Dongwon Kim and R. Paul Philp. School of Geology and Geophysics, University of Oklahoma, Norman, OK 73019-0628 [email protected]
Solid bitumen was recently identified within the Mississippian sandstone reservoir in the Hitch field, southwest Kansas. The adjacent Etzold field has similar reservoir properties but lacks the solid bitumen, although the Hitch and Etzold fields were thought to be in pressure communication and have a common source. A suite of the Hitch and Etzold crude oils and core extracts were analyzed by various geochemical techniques to gain a better understanding of the reservoir filling history and the geological and geochemical controls on the solid bitumen formation in the Hitch reservoir. A comparable study of crude oils and source rocks in the Anadarko basin was undertaken in an attempt to relate the oils to their possible source rocks.
Based on their biomarker distributions and carbon isotopic compositions, the Hitch and Etzold crude oils appear to be mixtures of hydrocarbons derived from Ordovician and Devonian (Woodford shale) source rocks. Geochemical evidence suggests that biodegradation and thermal alteration are not responsible for the formation of solid bitumen in the Hitch reservoir. The deposition of solid bitumen in the Hitch reservoir is more likely to be explained by the mixing of oils with different geochemical compositions from multiple source rocks filling the reservoir over an extended period of time. A possible reservoir-filling scenario revealed that the Hitch field oils are more heterogeneous in geochemical composition than the Etzold field oils due to multiple sources. Furthermore, gas deasphalting and regional pressure and temperature drops as a result of post-Laramide orogeny may have contributed to a phase change in the reservoir fluid to precipitate solid materials by disturbance of thermodynamic equilibrium.
AAPG Search and Discover Article #90067©2007 AAPG Mid-Continent Section Meeting, Wichita, Kansas