Railroad Gap Area--New Reserves in Old Province: ABSTRACT

Abstract

The Railroad Gap area, consisting of the Railroad Gap field and the deeper pools at Northeast McKittrick and McKittrick Front, is on the west side of the San Joaquin Valley near McKittrick, Kern County, California. The discovery of the Railroad Gap field in February, 1964, by the Standard Oil Company of California led to the deeper-pool discoveries at Northeast McKittrick and McKittrick Front by the same operator during the ensuing 1½ years. Anticlinal closure traps most of the reserves in each field. The folds differ considerably in size, configuration, and orientation. Normal and reverse faults are common, and cause differences in oil-water interfaces within the same accumulation. Nearly all stratigraphic units from the Eocent Point of Rocks Sandstone Member to the Pleistocene Tulare Formation are productive in the area. The primary objectives and most prolific reservoir rocks are the Oligocene Oceanic and the lower Miocene Phacoides and Carneros Sands. The massive Phacoides and Oceanic Sand units differ considerably in thickness and reservoir quality from place to place. The Phacoides permeability variations are particularly surprising, because initial completions range from 100 to 9,000 BOPD at similar structural positions within the same accumulation. The Railroad Gap area was known to be anticlinal, but conclusive evidence of critical closure on the northwest could not be documented by conventional structural studies or geophysical methods. Regional isopachous studies of the middle and upper Miocene, however, indicated the existence of thickness variations of a sufficient magnitude that potential northwesterly closure could be inferred to be present in the underlying lower Miocene sediments. The isopachous contours reflect middle and late Miocene structural growth along the trend, suggesting a favorable geologic history for the area. The lower Miocene and Oligocene, from nearby well data, were known to contain excellent clastic reservoirs, thus completing the knowledge necessary to justify an exploration program. End_of_Article - Last_Page 486------------