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Abstract: South Ellwood Field, Santa Barbara Channel: New Insight into Structures, Fractures and Seeps

CHRISTENSEN, KAREN, MICHAEL WRACHER, and  GARY ORR , Venoco Inc., Santa Barbara, CA 

The South Ellwood Field, discovered in 1964, was originally developed in the Miocene Rincon and Vaqueros Sandstones. The overlying Miocene Monterey Formation later was recognized as commercially productive and quickly became the primary reservoir. The field currently delivers 4500 BOPD and has produced 60 MMBO and 50 BCFG (1/31/2000). The field was re-interpreted in the mid-1980’s utilizing 1983 vintage 2D and 3D seismic data. Integrated geologic study continued in the early 1990’s based on the original structural interpretation. The South Ellwood field has always been mapped as a faulted, slightly asymmetric, elongate EW anticline with a major bounding reverse fault along the south flank and a long north flank. The prolific Coal Oil Pt seeps have generally been associated with the crest of the structures.

Venoco acquired the South Ellwood Field in 1997 and initiated a modern reservoir characterization study of the field. The 3D seismic was completely reprocessed and reinterpreted. A 3D geologic model was built incorporating the new seismic interpretation as well as logs, dipmeter, core and outcrop information.

Monterey stratigraphic picks have not changed significantly from previous interpretations. Improved seismic imaging has lead to important structural changes. The overall structural trap is a 2-way fault and dip trap with virtually no north limb. The northern bounding faults are large down-to-the-north normal faults, similar to the Refugio fault, which crops out to the north onshore. The La Goleta and Holly seeps are found where these north bounding faults intersect the seafloor.

Under the auspices of a DOE Class III grant, Venoco and the University of Southern California are studying the impact of this structural model on interpreted fracture orientation, fracture density and oil, gas and water production.

  ©Copyright 2000 American Association of Petroleum Geologists. All rights reserved.

 

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California