Petrophysical Evidence for the Nature of Vertical Permeability Barriers: Temple Ave. Fault, Wilmington Oil Field, Long Beach, California
H. Camacho and J. C. Sample
The Temple Avenue fault is a north-trending east-dipping normal fault that dissects the north flank of the Wilmington anticline in the Wilmington Oil field. The fault involves sediments of the Repetto Formation (lower Pliocene) and the Puente Formation (upper Miocene). Oil/water contact structural maps indicate that the fault acts as a permeability barrier.
Well B-756-I was drilled across the Temple Ave. fault in the Repetto Formation. The throw of the fault in this well ranges from 15 to 17 meters (50 to 56 feet). The Repetto Formation is composed of interbedded sands and shales. Sixty five samples were collected from and around the fault zone.
Preliminary XRD analysis of bulk and clay fractions show that authigenic clay minerals (<2 µm) represent between 1 to 2% of the sediments. Clay minerals are mostly smectite (5-7%) and a Fe-illite (15-30%); chlorite and kaolinite are also present. The authigenic illite content appears to increase around the fault zone. Diagenetic conversion of Ca-rich feldspars to smectite is suggested by an inverse correlation of their abundances. Calcite is present in the majority of the sampIes (4-8%), but a significanl increase in the carbonate content (14-16%) occurs along the fault. Ongoing SEM and isotope analysis will aid in the determination of the origin and nature of the changes in the mineralogy that contribute to form a permeability barrier.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California