Influence of fluid and operating parameters on the recovery factors and gas oil ratio in high viscous reservoirs under foamy solution gas drive

- Series of 16 pressure depletion tests carried to evaluate the features of foamy oil.
- Foamy oil behavior for four heavy oil-solvent systems were studied systematically.
- 4 systems: heavy mineral oil with methane, ethane, CO2 and crude oil with methane.
- Study investigates the effects of number of parameters on oil recovery trends.
- Each high viscous oil system was characterized by evaluating different parameters.

Foamy oil flow behavior is reported in several high viscous reservoirs in the world, wherein reduction of pressure was noticed to be the main factor of such characteristics. It is also believed to be a significant recovery mechanism in numerous high viscous heavy oil reservoirs that have revealed higher recovery factors when compared with the fluid flow using ordinary Darcy equation. This research investigates the effects of number of factors that influence the oil recovery trends, as well as the production rates in high viscous reservoirs under foamy solution gas drive behavior. The factors investigated comprised of refined mineral oil versus crude oil, saturation pressure, oil viscosity, drawdown pressure, flow direction, solution gas, pressure depletion rate and gas oil ratio (GOR). Live oil-gas system is prepared by blending a mixture of dead oil with gases such as CO2, ethane and methane. Each high viscous live oil system was completely characterized by evaluating fluid parameters and operating parameters. The significant outcome of the depletion tests confirms that the decreasing pressure depletion rate result in lower performance. At the similar rate of pressure depletion, higher oil recovery was obtained with methane saturated oil compared to either ethane/CO2 systems, even though it had the lowest solution GOR. At saturation pressure of 500 psi, the solution GOR was 9.1 m3/m3, 28 m3/m3 and 33 m3/m3 with methane, CO2 and ethane gas respectively, whereas solution GOR of methane saturated with crude oil were found to be 11 m3/m3. Both mineral and crude oil systems displayed similar decline in the oil recovery performance with decreasing pressure depletion rate. In high depletion rate tests, the recovery factor was 26.1%, 23.7% and 19.6% with respect to methane, ethane and CO2 respectively, whereas in slow depletion runs, the recovery factor declined from 13.1% with methane to 5.5% with CO2.