ABSTRACT: Heavy Oil Reservoirs in the Tulare Fold Belt, Cymric-McKittrick Fields, Kern County, California

Thomas Farley

The Tulare fold belt is a series of asymmetric, generally northeast-verging anticlines and synclines in the Pliocene-Pleistocene Tulare Formation that trend northwestward through the Cymric-McKittrick fields. Anticlines within the deformed belt generally originated as fault-propagation folds above decollements, the most important of which is the regional decollement on top of the Amnicola sand, the basal Tulare unit. The Amnicola decollement is the northeast subsurface extension of the McKittrick thrust, a low-angle fault that has displaced the Miocene Antelope shale over the Pliocene San Joaquin Formation and locally over the Tulare Formation. The Amnicola decollement is itself deformed by folding related to a younger, deeper decollement near the base of the San Joaquin ormation that merges westward with the Amnicola decollement and defines a zone of faulting associated with the McKittrick thrust.

Heavy oil reservoirs in the Tulare Formation are currently undergoing active development by thermal recovery techniques. In general, the geometry of heavy oil reservoirs is determined by location within the Tulare fold belt combined with the position of a subhorizontal fluid level trap that forms the updip limit of fluid-saturated rock. Reservoir geometry is complicated by complex local structure, discontinuous stratigraphy, and partial depletion of heavy oil reservoirs by fluid withdrawal due to gravity drainage. Proper resolution of fold geometry, fault geometry, and position of the fluid level trap is crucial to the design and monitoring of thermal recovery projects within the Tulare fold belt.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990