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