History of the Rio Bravo Field

History and reservoir performance of the Rio Bravo field, Kern County, Calif., are summarized. The Rio Bravo and Vedder zones have produced more than 100 million bbl of oil since 1937 with 125 wells completed in these zones. Efforts made to solve some rather unusual operating problems and to promote recovery are described. promote recovery are described. Introduction

The Rio Bravo field is located about 15 miles north-west of Bakersfield, Kern County, Calif. (See Fig. 1.) The zones of principal importance are the Rio Bravo and the Vedder; and, although a deeper Helbling and a shallower sequence of Pliocene gas sands are of economic importance, this report is limited to the Rio Bravo-Vedder reservoirs. These other zones, as well as field stratigraphy, have been discussed in previously published papers. The Rio Bravo field is classed as published papers. The Rio Bravo field is classed as a major oil field, having producing 108 million bbl of oil. As of Aug. 1, 1974, total gas sales have amounted to 56.8 Bcf. Discovery was based on reflection seismograph surveys. The discovery well was Union Oil Co. Kernco 1-34 (now Rio Bravo Unit Kernco 85-34), completed Nov. 4, 1937, at a total depth of 11,302 ft in the Rio Bravo sand. Initial production was 2,400 B/D of oil; 39.6 deg. API; 0.7 percent of water; and 1,260 Mcf/D of gas from 11,220 to 11,302 ft. After 30 days, production was 2,588 B/D of oil and 4,306 Mcf/D of gas. This was the first commercial producer in California below 11,000 ft, and for a short period it was the deepest producing well in the world. Although the first few wells were limited to the Rio Bravo sand, the underlying Vedder sand was opened to production in April 1938 in The Superior Oil Co. Wagner 2 well. Development ensued rapidly with the use of large steam-powered rigs, and by the end of 1941, when the U.S. entered World War 11, 97 wells had been completed, Also by that time, except for some edge-well drilling (mainly in 1954, 1955, and 1956), development was substantially complete.

Structure and Geology

Structurally, the Rio Bravo-Vedder pool consists of an elongated, asymmetrical dome with axis trending in a generally northwest-southeast direction. The accumulation of hydrocarbons, as in the somewhat similar Greeley field adjacent to the southeast, is controlled by anticlinal folding that occurs along the same directional trend. A major fault, also trending in a northwest-southeast direction, bounds a portion of the easterly limits of production in both fields. The Rio Bravo and Vedder are of Miocene age, the former overlying the latter, and separated by a thin, apparently competent, shale break. The Rio Bravo is a blanket sand covering the entire area of the field, which is about 2,300 acres, while the area of the Vedder is somewhat less. As seen from Fig. 2, which shows contours on top of the Rio Bravo, closure in this sand is about 400 ft. The 11,200-ft contour was the approximate average depth of the original water-oil contact. The two north-south normal faults through the easterly limits of Section 28 have not had a major effect on production.

Reservoir Rock and Fluid Characteristics

The Rio Bravo sand varies between 40 and 70 ft in thickness, and, in general, 75 percent or more of the zone is productive.

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