A Simplified Approach for Modeling PVT and Flow Behavior of Four-Phase Fluid in Solvent-Based Bitumen Recovery

Abstract A simplified approach is proposed to address the primary challenge in modeling the pressure-volume-temperature (PVT) and flow behavior of solvent-based bitumen recovery: the formation of two hydrocarbon liquid phases (a light liquid rich in solvent and another heavy liquid rich in asphaltene) when liquid solvent mixes with bitumen in reservoir. This novel method bypasses the complex and expensive flash calculation to determine the equilibrium of three hydrocarbon phases (two liquid phases and one vapor phase) and the phase-combination / heavy-liquid co-flow formulation for four-phase fluid flow (three hydrocarbon phases and one aqueous phase) in a compositional simulation. Based on evidence from multiple lab flow tests, field trials, and established simulation practices, a conclusion has been reached that modeling the PVT and flow behavior of heavy liquid is unnecessary for the compositional simulation of solvent-based bitumen recovery. As a result, a new equation of state (EOS) model along with a viscosity correlation is developed that completely rules out the formation of heavy liquid so that liquid solvent and bitumen are fully miscible, and solvent can vaporize at sufficiently low pressures. This simplified approach has been successfully implemented in CMG-GEM by leveraging the PVT and flow features already in the simulator. Its implementation in Schlumberger's INTERSECT is ongoing, which only requires limited effort to improve the viscosity correlation. Data from Imperial's field pilot of the Cyclic Solvent Process (CSP) was used to calibrate a simulation model coupled with the simplified EOS in CMG-GEM. The model was able to capture the key metrics of the entire pilot period, including the production of bitumen, solvent and water, and the bottom-hole pressures of the pilot wells. Compared to the full-physics approach, the simplified approach can be easily implemented in commercial reservoir simulators that are formulated to describe the PVT and flow behavior involving only one hydrocarbon liquid. More importantly, the outstanding run-time performance of simulation models based on the simplified approach has enabled the simulation of large-scale field developments, which is nearly non-viable for the full-physics approach. The successful history match of CSP field data with the CMG-GEM compositional simulation integrated with the simplified approach has further consolidated our understanding of the asphaltene precipitation, migration, deposition, buildup and the potential for flow impairment in the reservoir as well as the near-wellbore region. This knowledge has been leveraged in the asphaltene studies of other company assets.