Enhanced Cyclic Solvent Process (ECSP) for Heavy Oil and Bitumen Recovery in Thin Reservoirs

Abstract

Appropriate techniques have to be developed for improving heavy oil recovery from thin reservoirs in western Canada, where thermal methods suffer from heat loss to overburden/underburden and vapor extraction (VAPEX) is not effective because of the lack of efficient gravity drainage. Considering this, a hydrocarbon gas injection process in huff-n-puff mode, i.e., traditional hydrocarbon-based cyclic solvent process (CSP), has been tested to evaluate its applicability to such thin reservoirs. In the first part of this study, the behavior of methane huff-n-puff for heavy oil recovery is investigated by conducting a series of CSP cycles in a sandpack saturated with crude oil (with a viscosity of 1080.6 cP at 22 °C) and brine. The results of the six methane CSP cycles revealed that methane huff-n-puff is inefficient. The problem is that, during the production cycles, the reservoir pressure has to be greatly reduced to realize solvent gas drive. In doing this, the oil regains its high viscosity, because a large fraction of methane evolves out of the oil. To overcome this limitation and keep the oil viscosity low by maintaining most of the viscosity-reducing solvent in oil during the production period, we examined a new process, enhanced cyclic solvent process (ECSP). In ECSP, two types of hydrocarbon solvents are cyclically injected but in two separate slugs. One slug is more volatile (methane), and the other is more soluble (propane) in the heavy oil. A series of six ECSP cycles was conducted in the same sandpack used in the methane huff-n-puff tests. A total recovery of 34.30% original-oil-in-place (OOIP) was obtained through six ECSP cycles compared to 4.27% OOIP of six methane huff-n-puff cycles, indicating that ECSP improves the methane huff-n-puff for the heavy oil recovery in thin formations.