CASCADE OIL FIELD, ECONOMIC AND SCIENTIFIC SIGNIFICANCE

Cascade oil field is located along the northern margin of San Fernando basin. Since its discovery in 1954, this field has produced two million barrels of 23° gravity oil from shallow conglomerates of the Pliocene Saugus formation. In 1990, production was established from deeper Pliocene reservoirs and potential production identified within Miocene rocks. The stratigraphy at Cascade field is very similar to Aliso Canyon field, immediately to the west. The structure of Cascade field is an ENE plunging structural nose cut off on the west by the Cagney-Mission fault. At deeper levels the fold trends more east-west and is very tight with dips up to 80°. The field is caught up in splays of the Santa Susana fault and a large south-dipping, E-W trending, axial fault. Deeper zones have proven potential to significantly increase production but untill recently, low oil prices coupled with expensive wells have slowed development and further exploration of these zones. Cascade field occurs near the westward extent of a rupture zone which developed on the Santa Susana fault during the 1971 San Fernando earthquake and along a major change in trend in the Santa Susana fault from E-W to NE-SW. This change in trend has been attributed to a downward flexure in the fault surface but may in fact be due to the NE-SW trending cross fault which forms the western boundary of Cascade field. Future drilling of the deeper zones at Cascade field will have significant economic benefits to the operator; understanding the scientific data gathered by this drilling will increase our understanding of the Santa Susana Fault and of the major earthquake hazard it represents.