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Abstract: The Use of Horizontal Drilling to Improve Production from a Tight P1iocene Reservoir, Westem Shallow Oil Zone: Elk Hills, U. S. Naval Petroleum Reserve #1, Kern County, California


The Gusher and Calitroleum sands, Lower Pliocene aged Etchegion Formation, are the lowermost oil-productive units in the interval referred to as the Western Shallow Oil Zone (WSOZ) at the Elk Hills Naval Petroleum Reserve, Kern County, California. They are silt-size to very fine grained, contain as much as 35% clay, have good porosity (28% avg.) but poor average permeability (<10 md), and are extremely fresh water sensitive. Formation pressure ranges from 1100 to 1800 psi, depending on the degree of depletion. Cumulative oil production from the Gusher and Calitro1eum ranges from 15,000 to 312,000 barrels, per well, for those drilled between 1976 and 1983. Most wells are commingled Gusher Calitroleum and many have had other Shallow Oil Zone sands added. Production appears to be dependent primarily on sand quality and clay content. Vertical wells have been drilled and completed in these reservoir on a 20 to 30 acre spacing. After 20 years of production, vertical wells completed in these sands are believed to have drained less than ten acres each. Gusher and/or Calitroleum sands were fracture stimulated in ten wells between 1978 and 1990. The frac jobs were considered to be of mixed results due to the variety of frac parameters utilized over the years as well as the variety in quality of reservoir rock that was treated. Cumulative production has been estimated to be less than five percent of the original oil in place.

In an effort to recover more oil from these tight reservoirs, a horizontal well program has been initiated in the Calitroleum sands at Elk Hills The wells were designed to follow a path along strike within the better quality reservoir rock, based on the character of the resistivity curves. If proven successful, additional horizontal wells will be planned for the Gusher sands

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California