Buena Vista Hills (27-B Pool): ABSTRACT

Abstract

The Buena Vista oil field is situated on the southwestern edge of the Great Valley of California immediately north and east of the town of Taft. It has produced oil since 1909 from two formations, the San Joaquin clays and Etchegoin, both of Pliocene age. Although the 27-B pool was not discovered until March, 1944, the sand had been penetrated as early as 1915, but because of unfavorable structural position, no production was realized. The hills consist of two major anticlines, the United and the Honolulu, in northwest-southeast echelon, each anticline having separate closure, but with production continuous across the saddle. Limiting closure is determined at the intersection of the United anticline on its northwest plunge, with the Midway Valley syncline. Closure in the Pliocene increases End_Page 129------------------------------ with depth, due to over-all thinning in a southeasterly direction, to a point of minimum section at about the NW. ¼ of Sec. 9, 32-24. The southwest flanks of the folds are locally oversteepened, without resultant shift of axes, suggestive of similar folding. A probable fault, referred to as the Maguire fault, separates the old Maguire sand pool from the 27-B pool. The Maguire sand is considered to be the southeastern extension of the 27-B sand. The assignation of the 27-B sand to the Etchegoin (Pliocene) is considered erroneous. Conclusive faunal evidence is lacking, but from other evidence available at present, a Pliocene-Miocene break is preferred above the 27-B sands. A maximum net sand thickness of about 110 feet occurs in Sec. 36, 31-23. The individual sand lenses (E1-E4) pinch out not far downdip on the northeast flank of the hills, at higher structural elevations than is the case on the southwest flank. This is the apparent reason for the much higher water table on the northeast flanks,--a case of water entrapment against a permeability barrier. Edge water on the southwest flank is found to be 300 feet structurally lower than the structural spill point. This is explained by pinch-out of the individual sand lenses in the W. ½ of Sec. 28, 31-23. At the peak of the war demand the pool produced at average rates as high as 40,275 barrels per day. The current maximum efficient rate is set at 25,000 barrels per day, which permits top wells a daily production of 180 barrels, subject to a gas restriction in the case where a well produces gas at rates in excess of 600 cubic feet per barrel. The absence of a water drive will probably require some form of pressure maintenance for maximum oil recovery. End_of_Article - Last_Page 130------------