Hydrocarbon Leakage Through a Paleochannel Across Faults: A Case Study in Wilmington Oil Field, California

Linji An
Aera Energy LLC, 10000 Ming Avenue, Bakersfield, CA 93311

The impact of a submarine channel in western Wilmington Oil Field, California, on hydrocarbon accumulation and the sealing property of boundary faults are evaluated. The coarse channel deposit named T4 is within Tar zone, a Lower Pliocene turbidite deposit and also the topmost oil production zone in the studying area. The channel deposit was identified during detailed reservoir characterization, which includes mapping all the significant sand units in the area, and determining oil water contact (OWC) for each unit through detailed well log examination. From tilted OWC’s, crossover of OWC with structure depth contour lines, and fault seal analysis, it is concluded that the channel deposit has caused, and is causing, hydrocarbon leakage across the boundary faults. The leakage takes place in the three channel-incised sand units in Tar zone: T2, T5 and T7. In Fault Block I, hydrocarbon in the three sand units pools into the channel deposit, leaks into a thick and wet sand unit named S at the very top of Tar zone in Fault Block IIA. In Fault Block IIA, hydrocarbon from T2, T5 and T7 sand units also pools into the channel sand, and leaks into S sand in Fault Block IIB. The channel related fault leakage caused depletion of almost all hydrocarbon in the three channel-affected sand intervals in Fault Block I where the channel is located near the crest of the Wilmington anticline. It also reduced hydrocarbon reserve on north flank in Fault Block IIA.

AAPG Search and Discovery Article #90076©2008 AAPG Pacific Section, Bakersfield, California