CLARKE, DONALD, Department of Oil Properties, Long Beach, CA

ABSTRACT: Timing and Movement on Growth Faults in the Wilmington Oil Field: A Computer-Aided Mapping Study

The Wilmington oil field was formed by post middle Miocene structural deformation in the Los Angeles basin. This deformation resulted from the right lateral shear and compression occurred between the North American and the Pacific plates. Observations indicate that the faulting was episodic and contemporaneous with deposition.

Computer mapping of detailed stratigraphy has enabled faulting in the East Wilmington oil field to be seen in a new light. The vertical section has been subdivided into 60 units, each with a structure map and an isochore map. Limit data and paleontological data have also been added. The 30 faults currently mapped vary greatly in their effects on the oil reservoirs. The faults act as barriers that separate the various reservoirs and as partial barriers within the reservoirs. Specifically, we are looking for horizontal and vertical fault separation, actual displacement when possible, and the timing of fault movement.

What has been observed so far is that none of the faults break the surface. There is some evidence of slight deformation of near-surface sediments above the Long Beach Unit fault. Most faulting appears to terminate at unconformities. Unconformities include a Pliocene-Pleistocene unconformity, a Pliocene unconformity, and a Pliocene-Miocene unconformity. Other unconformities certainly exist but have not yet been located and mapped over the entire field. Deposition during the periods of faulting, compaction, and channeling must also be considered. The knowledge gained here will be applied to further enhance the optimized waterflood.

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