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

Summary 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 Venezuela) 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 solution 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 approximately 3 months. The following conclusions are drawn based on the results from all the tests. Initial water saturation decreases gas-bubble density. The recovery efficiency decreases because of an 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, which in turn results in a reduction of 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 the gas-bubble nucleation process, mainly because of change in interfacial tension. For all the tests conducted, the oil recovery by solution-gas drive at test termination was approximately 16% and higher.