Evaluation of COFCAW as a Tertiary Recovery Method, Sloss Field, Nebraska

Following an encouraging pilot test, a full-scale COFCAW (Combination Of Forward Combustion And Waterflooding) operation was conducted in the Sloss field, Nebraska. Begun with six 80-acre 5-spots, this project ultimately involved 960 acres and became the largest test of tertiary oil recovery yet reported. Reservoir conditions were unusual for thermal recovery. The reservoir had previously been waterflooded to an average residual oil saturation of 30% PV or less. It was thin (14 ft), deep (6,200 ft), hot (200$F), moderately porous (19%) and permeable (191 md), and it contained a light (39$API) oil. COFCAW proved to be operable but uneconomic in this lean reservoir. Injectivity was substantially lower than in the pilot, partly due to the use of oil reworked injection wells. Corrosion and erosion also were more serious and more expensive than in the pilot. Oil producing rates up to 500 bopd were achieved. Injected air-water ratios as low as 400 SCF/bbl appeared to be advantageous. Sweep efficiency of COFCAW has not yet been completely evaluated, but appears not to exceed 50% greatly. (11 refs.)