Steam Injection Into the D and E Zone, Tulare Formation, South Belridge Field, Kern County, California

Abstract

A portion of the D and E zone of the Tulare formation reservoir produced by pressure depletion for 22 years and by cyclic steam produced by pressure depletion for 22 years and by cyclic steam for 4 years. Because of low recovery, diminishing response, and well failures, new wells were drilled in 1969 to initiate continuous-steam injection. Cumulative recovery from the first-line wells is 26 percent of the original oil in place, more than double the estimated primary recovery. place, more than double the estimated primary recovery. Introduction The portion of the Tulare formation D and E zone sands discussed here is located in Sections 1, 2, and 12, T29S-R21E, in the South Belridge field, Kern County, Calif. Although the field was discovered in 1911, development of the area did not begin until demand for additional heavy crude occurred in 1943. Drilling started in May 1943, and by Dec. 1944 a total of 40 wells were producing on about 5-acre spacing. The oil rate reached a peak of 1,000 B/D and declined at a rate of 12 percent per year. Production was essentially by pressure depletion. Production was essentially by pressure depletion. Cyclic steam operations were initiated in the area in 1965 with excellent results. Although results were initially spectacular, decline was rapid despite repeat cycles. Well failures were numerous. Combustion and continuous-steam injection pilots were carried out in other parts of the field, Evaluation of these two methods indicated that the most desirable economics would be obtained by continuous-steam injection. This area was selected for a large-scale steam drive test. The test was initiated in April 1969. Oil recovery from May 1943 to April 1969 from this area was 3.2 million bbl, or 8.7 percent of the original oil in place. Pressure had declined to 180 psig. Pressure had declined to 180 psig. The test was carried out in two stages, with continuation dependent on the success of the first stage. Because of mechanical conditions of wells in this area, it was decided to redevelop the area using the best thermal techniques. Case histories of other steam injection projects have been reported in the literature. Reservoir Characteristics The over-all structure of the South Belridge field is a broad, southeasterly plunging anticlime, about 9 miles long and 2 miles wide, with sands deposited in a halo-like fashion around the flanks and with shaley sands across the axial portion. The study area is located on the northeast flank of Mobil Oil Corp's portion of the South Belridge field, as shown in Fig. 1. The area is about 1.7 miles long and 0.2 miles wide, with a dip of 7 degrees to the northeast. Structural contours, a type log, and the boundaries of the area are shown in Fig. 2. Within the D and E zone there are numerous individual sands that vary in thickness. This is shown in cross-section X-X' of Fig. 3, where the sands of the D zone are relatively thick down-structure but become thin, and in some cases disappear, up-structure. Cross-section Y-Y' of Fig. 4 also shows the variation in sand thickness and character. Sand correlations are often difficult. An isopach of net oil sand in the D and E zone is shown in Fig. 5. Within the area of study, the total net oil sand is a maximum of 130 ft down-structure and thins to 70 ft up-structure. P. 343