Effect of GOR, Temperature, and Initial Water Saturation on Solution-Gas Drive in Heavy-OIl Reservoirs

Abstract

Abstract We have carried out an extensive set of tests on solution-gas drive for a heavy oil to study the effects of initial water saturation, temperature, and gas-oil-ratio (GOR). The viscosity and the API gravity of the stock tank oil from Hamaca field (in Venezulela) used in our tests are 560,000 cp (at 24°C) and 8.7, respectively. The solution-gas drive tests were conducted using live oils with GOR of 6.5, 9.0, and 12.2 (vol/vol at standard conditions). In two tests, initial water saturations of 4.0 and 5.2% were established. Five tests were conducted at a temperature of 35°C; one test was conducted at 46°C. The duration for each test was around three months. Based on the results from all the tests the following conclusions can be drawn. Initial water saturation reduces gas-bubble density. The recovery efficiency decreases due to increase in gas mobility with increase in initial water saturation. As the temperature increases from 35 to 46°C, the gas relative permeability increases one order of magnitude; as a result there is reduction in recovery efficiency. The temperature effect on recovery is in agreement with our previous work with temperature increase from 24 to 35°C. Increase in solution GOR has a significant effect on gas-bubble nucleation; there is a systematic increase of the critical gas saturation with GOR increase. For all the tests conducted, the oil recovery by solution gas drive at test termination was about 16 percent and higher.