Dimethyl Ether as a Novel Solvent for Bitumen Recovery: Mechanisms of Improved Mass Transfer and Energy Efficiency

Abstract

Summary A solvent-based thermal recovery process has the advantages of low capital expenditure, less energy consumption, and less greenhouse gas emission. Dimethyl ether (DME), as a renewable solvent, has been considered as a novel additive in the thermal bitumen recovery process. Being soluble in both water and oil phases, DME has the potential to enhance mass transfer and improve oil production. In this work, a phase behavior model of the DME-bitumen-water system is first developed considering DME partitioning between oil and water. A field-scale numerical simulation model with fine gridblocks is developed to investigate the heat and mass transfer mechanisms between DME and bitumen in the interface of a DME vapor chamber. The numerical model is validated with physical experiment results. The close agreement between measured and simulated production profiles indicates that the mechanisms are adequately captured. Meanwhile, various simulation scenarios are performed to evaluate the production performance and the energy efficiency, which is defined as the energy/oil ratio. It is found that the oil production rate in DME injection is 15% higher than that in butane injection at the early stage of production. The solvent penetration depth in DME injection is larger than that in butane injection. This is attributed to the enhanced mass transfer between DME and bitumen caused by the high diffusion of DME in the water phase and preferential partitioning of DME into the oil phase. Furthermore, energy consumption in the warm DME injection process is 48% less than that in warm butane injection and 75% less than that in steam-assisted gravity drainage (SAGD). This is because DME injection can be operated at a lower-temperature condition, leading to less energy transferred to heat reservoir rock/fluids and less heat loss to over/underburden. Therefore, DME is proved to be a technically promising and environmentally friendly solvent to enhance bitumen recovery. The DME-based thermal recovery technique exhibits superior advantages in unlocking poor-quality reservoirs, especially in high water saturation reservoirs and thin reservoirs.