Harmattan Elkton Field - A Case for Engineered Conservation and Management

Abstract

Abstract The Harmattan-Elkton field, located approximately 50 miles north of Calgary, Alberta, Canada, is a major oil reservoir with a large associated gas cap in the Turner Valley formation, Rundle group of Mississippian Age. The ratio of gas-cap to oil-zone volume is 3.29, and the condensate content of the gas-cap gas was approximately 47 STB/1 million cu ft of gas at original reservoir pressure. The oil zone is partially overlain by gas and partially underlain by a limited water leg. Both gas and water coning have been experienced in the oil rim. The unitization of this field and the application of engineering techniques early in the productive life of the field have resulted in the adoption of a gas conservation program in the oil zone and a gas-cap cycling operation, which should result in the conservation of hydrocarbon products and an enhanced income for the field operators. Introduction The Harmattan-Elkton field is located approximately 50 miles northwest of Calgary, Alberta, Canada, as shown on Fig. 1. The field is a stratigraphic trap containing a large gas cap with a relatively thin oil column underlain by a limited aquifer. The oil-zone wells have a tendency to cone both gas and water, depending on structural location of the well and position of the perforations. This coning condition resulted in loss of producing rate under nonunitized operations due to gas-oil ratio and water-oil ratio penalties. Early in the life of the field, an operators' committee was formed to study the problems associated with producing the field, and, in 1960, detailed engineering work was begun to determine the best method of operation considering both conservation and income. The field was unitized in Dec., 1960, at which time the injection of casing-head gas into the gas cap was commenced. Cycling of the gas cap was initiated in March. 1962, at a design rate of approximately 105 MMscf/day. This operating program has performed successfully to date, has increased recoveries of gas-cap liquids due to reduction in retrograde losses, and has permitted the oil zone to produce at full allowable rate. This paper deals with the producing problems of the Harmattan-Elkton field and the ultimate solution of these problems. Geology The Harmattan-Elkton field produces from the Turner Valley formation of the Rundle group of Mississippian Age at an average depth of approximately 8,800 ft. The oil and gas accumulation occurs in a monoclinal stratigraphic trap dipping westward at approximately 1 degrees. Loss of permeability occurs along the northern, eastern, and southern flanks due to solution channels which have subsequently been filled with dense limestone. Production down-dip to the west is limited by an oil-water contact at a depth of 5,442 ft subsea. The original gas-oil contact occurred at a depth of 5,360 ft subsea. JPT P. 1171ˆ