Geochemical Characterization of Solid Bitumen Deposited within the Mississippian Sandstone Reservoir of the Hitch Field, Southwest Kansas

Dongwon Kim

School of Geology and Geophysics at the University of Oklahoma

Norman, Oklahoma 73019-0628

[email protected]

Solid bitumen was recently identified within the Upper Mississippian (Chesterian) 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 study the geological and geochemical controls on the formation of solid bitumen. 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 are 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 field. The deposition of solid bitumen in the Hitch reservoir appears 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 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 Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid