Abstract
The methane pressure cycling process is an enhanced oil recovery scheme intended for application in some heavy oil reservoirs either after termination of primary, or waterflood, production. The essence of the process is the restoration of the solution gas drive mechanism. The restoration is accomplished by re-injecting an appropriate amount of solution gas (mainly methane) and then re-pressuring the gas back into solution by injecting water until about original reservoir pressure is reached. This, aside from the replacement of produced oil by water, re-creates the primary production conditions. This novel recovery technique is being developed to target the considerable portion of heavy oil resource located in thin reservoirs. Primary and secondary methods have managed to recover at best 10% of the initial oil-in-place. Heat losses to overburden and underburden or bottomwater zones make thermal methods unsuitable for thin reservoirs.
Coreflood tests in 30.5 cm (length) H 5.0 cm (diameter) sandpacks were carried out for oils with a range of dead oil viscosities from 1,700 to 5,400 mPa.s. The results showed that the pressure cycling process could create a favorable condition for recharged gas to contact the remaining oil in reservoirs. This restores the situation whereby substantial amounts of gas are in solution for further "primary" production. The effects on the efficiency of the methane pressure cycling process of cycle termination strategy, oil viscosity, and mobile water saturation were investigated. Simulations were conducted to investigate the methane pressure cycling process in three heavy oil reservoirs in Saskatchewan, Canada. The effects on the process of infill wells, oil viscosity, gas injection rate, and the presence of wormholes in reservoirs were studied.
