As for the vast heavy oil reserves in Western Canada, a non-thermal primary production process called Cold Heavy Oil Production with Sand (CHOPS) is the most common method. In addition to inducing foamy oil flow, this primary production process which results in formation of high permeability channels in unconsolidated sand reservoirs known as “wormholes” typically recovers only 5-15% of original oil in place. As a result, new follow-up enhanced oil recovery (EOR) techniques are required in post-CHOPS reservoirs where experiences have shown that injection of either steam or solvents into such depleted reservoirs for EOR are not efficient and effective. Recently, the hybrid steam-solvent injection has been considered as the most promising EOR method for the post-CHOPS reservoirs, provided that the wormhole network can be accurately characterized. Physically, thermal energy can greatly reduce heavy-oil viscosity, while injecting solvents (e.g., CO2, flue gas, C3H8, and n-C4H10) can artificially restore solution-gas drive and carry thermal energy further into the formation. Addition of alkane solvents physically accelerates dissolution of CO2 into heavy oil, while N2 functions to boost and maintain reservoir pressure. In this paper, techniques have been developed to evaluate performance of thermal, solvents, and hybrid thermal-solvent processes in a post-CHOPS reservoir with consideration of wormhole network. With the experimentally determined properties of injected gases and reservoir fluids by performing PVT tests, history matching is accomplished for the reservoir geological model conditioned to the fluid and sand production profiles together with pressure. Meanwhile, the wormhole network is characterized with the newly developed pressure-gradient-based (PGB) sand failure criterion. Once the history matching is completed, the calibrated reservoir geological model is then employed to evaluate several scenarios of thermal, solvents, and hybrid thermal-solvent processes under various conditions. It is found that huff-n-puff processes perform better than either the continuous injection or water-alternating- gas processes when wormhole network is fully generated and propagated. Among all solvent-based methods, pure CO2 huff-n-puff process shows a better performance than flue gas, while the addition of alkane solvents leads to a higher oil recovery compared with CO2 only method. Since the addition of C3H8 and n-C4H10 will significantly decrease the heavy oil viscosity and enhance the swelling factor, the hybrid thermal-solvent injection achieves the highest oil recovery by taking the advantage of both hot steam and solvents injection.

Performance Evaluation of Hybrid Thermal-Solvent Injection in a Post-Chops Reservoir With Consideration of Wormhole Network

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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