Identification and Delineation of Low Resistivity, Low Permeability Reservoirs Using Qualitative Sidewall Sample Log k * S0 Relationships in the Western Shallow Oil Zone, Elk Hills Field, California
E. Kevin Beacom and Ira S. Kornreich
Over 500 wells, including wells producing from the deeper Miocene Stevens sands, penetrate the Western Shallow Oil Zone (Pliocene Etchegoin Formation) at the Elk Hills Naval Petroleum Reserve in California. The Western Shallow Oil Zone Gusher and Calitroleum sands are very fine grained, silty and pyritic and are interbedded with silty shales. Electric logs generally show 1 1/2-2 1/2 ohm-meters of deep resistivity and the spontaneous potential displays little or no response to the sands. However, approximately 180 wells in each of the mapped productive sands have sidewall sample data to visually inspect the rock for hydrocarbons.
Each productive interval within the Western Shallow Oil Zone has two or more pools. The most exploited (and most heavily drilled) of these pools is at the western end of the Eastern anticline. The pools on the Western anticline have few tests and production is limited and generally commingled.
In order to identify productive intervals and to delineate the areal extent of these sands, qualitative assessment of sidewall sample data was done and maps of log permeability times oil saturation were prepared for each zone. The analysis showed large amounts of unexploited hydrocarbons in the Western pools. Complete exploitation of the Gusher and Calitroleum sands will recover in excess of 11 million additional barrels of 38 degree gravity oil.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California