The use of steam injection for high viscosity oil fields is popular in the petroleum industry due to its success in increasing bitumen recovery rates. Recent studies in the past decade, including simulations, experiments and pilot tests suggest that the co-injection of hydrocarbon solvents can further increase production rates over steam alone. However, the immiscibility and equations of state (EOS) discontinuity between hydrocarbon solvents and water makes predictions for thermodynamic property changes difficult. As a result, the selection criteria for finding the optimum molecular weight of the co-injecting solvent is often based on a “guess and check” approach through both reservoir simulators and laboratory testing. In order to properly determine a beneficiary solvent for co-injection with steam, the thermodynamic principles and physical interactions between the separate phases of the injected fluids must be fully understood. Unfortunately, commercial thermal simulators do not accurately determine compositional changes within a thermal setting as such programs utilize K factor compositional equations which is far more error prone EOS based compositional equations. This research demonstrates the thermodynamic mechanisms occurring between the different phases of water and solvent through a thermodynamic simulation program. This program couples EOS with saturated water correlations to mechanistically model the characteristics of all fluids and phases individually while still considering their interactions. The composition and phase changes of the system during the heat transfer process are also identified, enabling EOS calculations to be updated with more accurate fluid data. Through detailed calculations of thermodynamic processes, an explanation is given to exactly why temperature changes are observed in steam when in the presence of a light hydrocarbon. This allows for the fundamental understanding of the physical interactions that occur within the injected fluids of a solvent assisted steam injection, particularly in a controlled setting such as an experimental reservoir model. However the program may still be used independently from any experimentation to gain a conceptual understanding of the thermodynamic interactions between steam and solvent during a condensation process.
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