Fireflooding Shallow Tar Sands - A Case History

Abstract

Abstract A field pilot test of forward combustion utilizing fracturing techniques was conducted in a shallow tar sand deposit in central Kentucky. The tar sand at a depth of 100 ft had an average porosity of 22%, an oil saturation of 64% (6.4% tar by weight) and a permeability after extraction of about 2000 md. The tar had an API gravity of 10.4 º and a viscosity of 150,000 cps at a reservoir temperature of 561JF. The pilot area, was a small inverted fivespot 107 ft on a side. Horizontal fractures were created on the four producing wells by breaking down the formation with air pressure, and these fractures were propped to a calculated radius of 25 ft by injecting water-base gel carrying 4–8 mesh sand. A pneumatic fracture was created in the central injection well, which was held open by the continuedinjection of air. A down-hole burner was used to initiate the combustion zone. Oil production responded to the movement of the combustion zone ten days after the fireflood was started. The average oil production was 24 barrels per day for the four months required to complete the test. The total oil production of 8100 barrels was 54% of the 5700 barrels originally in place in the pattern area. The injected air produced oil ratio was 42,000 cu. ft/bbl. The produced oil was upgraded to 14.5 API and 2000 cps at 60 ºF, compared to 10.6 º API and 90,000 cps for the original tar at the same temperature. The major problems encountered were the lack of complete oxygen consumption, the unsymmetrical advance of the fireflood and the tendency of the combustion zone to move toward the top of the reservoir. Introduction During 1959 and 1960, Gulf Research & Development Co, conducted a fireflood field pilot test in a shallow tar sand deposit lying about halfway between the towns of Brownsville and Leitchfield, Kentucky. The property had been leased from the Kentucky Rock Asphalt Co., hence the name KYROCK. The fireflooding or forward combustion method has been adequately described elsewhere.(1, 2, 3, 4) and the modification tested at the Kyrock site was the utilization of both pneumatically and mechanically propped fractures. Earlier reverse combustion experiments in the tar sand deposit had indicated that horizontal fractures could be extended at constant depth over considerable distances and that a forward combustion reaction zone could be maintained using these fractures for a major part of the fluid flow. Although the results of these tests were encouraging, neither further development of the method nor publication of the results was warranted at that time because tar sand production could not compete economically with the adequate supplies of conventional crude. In the last few years, that situation has changed and now supplies of hydrocarbons from any and all sources are needed to augment the declining rate of domestic production.