Field Case: Cyclic Gas Recovery for Light Oil-Using Carbon Dioxide/Nitrogen/Natural Gas

Abstract

Abstract Cyclic gas recovery ("Huff and Puff") using carbon dioxide has been applied successfully in the Big Sinking Field of eastern Kentucky. The process was initiated in 1986, and was used continuously until 1994, with 390 treatments on 240 wells. A total of 12,200 tons of liquid carbon dioxide resulted in additional recovery of 180,000 barrels of oil. Successive cycles became less efficient, and a changing market for liquid carbon dioxide resulted in a 50% increase in price. The process was continued with rich gas (1900 Btu casing head) and exhaust gas (80% nitrogen and 20% carbon dioxide). Both gases were tested in two separate areas of the field where cyclic carbon dioxide had been performed successfully. In both cases the gas channeled within days to offset wells with little incremental recovery. The offset wells affected were located in the northeast/southwest natural fracture trend. The offset wells were shut in and allowed to soak and the input well was shut in after the designated volume was injected. Both the input wells and the offset wells had production increases. The exhaust gas increased the production six times over the initial production rate, and after two years of production response, the estimated ultimate recovery is O.85MCF/bbl. In the cyclic rich gas the ultimate recovery is estimated to be 3.3MCF/bbl. With no significant increase in operating cost, the primary cost of the process was in the investment in gas supply and injection. These additional tests show that in a light oil pressure- depleted resefl'oir with natural fracturing. cyclic rich gas and cyclic nitrogen/carbon dioxide mix can yield excellent recovery efficiencies, and can be more efficient than cyclic carbon dioxide, P. 501