MILLIKEN, M. D., U.S. Department of Energy, Tupman, CA, H. DEUTSCH, Bechtel Petroleum, Tupman, CA, and G. S. McJANNET, U.S. Department of Energy, Tupman, CA

ABSTRACT: Structurally Controlled Miocene Deep Sea Channels of the Stevens Zone, Elk Hills Field, Kern County, California

The Stevens zone of Elk Hills field consists of thick, massive, deep water channel sands, turbidites, and basinal shales stratigraphically equivalent to the upper Miocene Monterey Shale Formation. The two main channel fill sand bodies (referred to as 24Z and 26R) form important oil reservoirs. Oil trapping mechanisms include combinations of structural and stratigraphic features. The sands bank against time-equivalent and much less permeable silicic shales of the Monterey and possibly Reef Ridge Formations. Fine-grained sediments as levee overbank muds commonly form seals to vertical migration. The older channel, 26R, was directed between the rising en echelon 29R and 31S anticlines. The channel between the two anticlines requires an 180 degrees change in direction from southeast to no thwest. Crevasse splays broke out from the main channel along the apex of the 180 degrees bend, forming good reservoir rock. Other 26R crevasse splays occurred a short distance downchannel and may be responsible for the Stevens A4A6 and Tl-T4A sands of the eastern area of the Northwest Stevens pool. The younger 24Z channel differs significantly from the 26R channel in that its course seems oblivious to anticlinal structures, for it cuts perpendicularly across the 29R and Northwest Stevens fold axes. In the Northwest Stevens pool, the 24Z channel contains the Al, A2, and A3 sands. The sharply defined channel boundaries in section 7R resulted from imposing topographic sea floor escarpments. The origin of the 24Z and A1A2 escarpments is under debate; Elk Hills workers have variously interpr ted them as flexures, normal faults, and high-angle reverse faults.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.