Numerical Investigation of Solvent and Thermal Hybrid Processes for Thin Heavy Oil Reservoirs
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Western Canada has the second largest oil resources in the world. Over 90% is heavy oil and bitumen. Vapour Extraction (VAPEX), similar to Steam Assisted Gravity Drainage (SAGD) but using solvent to reduce the oil viscosity, has been proposed to produce heavy oil reservoirs in an environmentally sustainable way. However, while this process might work well for thicker reservoirs, such as those in Alberta, it will likely not meet economic thresholds for thinner reservoirs, such as those in Saskatchewan. The low flow rate in the pure VAPEX process is mainly due to three reasons: low mass transfer rate compared to thermal transfer rate, poor communication efficiency between the injector and the producer because of the reservoir heterogeneity and long distance between the injector and the producer, and poor horizontal well conformity. In this thesis, two categories of thermal and solvent hybrid processes are investigated to enhance the oil recovery for thin heavy oil reservoirs: electrical resistive heating with solvent injection and steam with solvent co-injection in both SAGD and Cyclic Steam Stimulation (CSS). Both categories are numerically investigated by using CMG’s STARS. Electrical resistive heating with solvent injection (ERH-S), a novel process, is presented and investigated to enhance the communication efficiency between the injector and the producer. This process can also improve the horizontal well conformity. The electrical heating is the most suitable to be coupled with the solvent process since the electrical heating (1) generates uniform heating results along the horizontal wellbore; (2) increases apparent permeability along the wellbore; (3) is not affected by the reservoir heterogeneity, such as thief zones and shale; (4) reduces water cut; and (5) reduces the formation damage caused by asphaltene precipitation. Through the numerical simulations and analysis, ERH-S shows three features that contribute to the enhanced oil flow: (1) the heat from the electrode establishes good communication between the injector and the producer by viscosity reduction; (2) the in-situ generated heat through ERH along with the horizontal wellbore is not susceptible to reservoir heterogeneity, and, thus, the horizontal well conformity can be improved; (3) the solvent can reduce the viscosity of the heavy oil in unheated zones where the ERH cannot reach, and it can also assist viscosity reduction of heavy oil in the heated zone. The simulation results show that this hybrid process can improve the oil rate 2 to 5 times over VAPEX. SAGD and CSS are two successfully applied enhanced heavy oil/bitumen production techniques. When these two techniques are applied in thin heavy oil reservoirs, due to the significant heat loss, the Steam-Oil Ratio (SOR) is too high to make these techniques economical. Simulations for steam with solvent co-injection, SAGD with solvent, and CSS with solvent show that under similar temperature and pressure between solvent dew points and operating conditions, the solvent injection can show better Cumulative Steam-Oil Ratio (CSOR). This study indicates that the hybrid processes using thermal and solvent have great potential to recover Western Canada’s thin heavy oil/bitumen reservoirs. It is recommended that laboratory investigation should be conducted in future.