Production Optimization of a Rigorous Thermal and Compositional Reservoir Flow Model

We model thermal and compositional reservoir production as mass and energy balances combined with a phase equilibrium constraint. The phase equilibrium constraint is modeled as a thermodynamically rigorous UV flash process. The UV flash problem is a mathematical statement of the second law of thermodynamics, and it replaces the condition of equality of fugacities that is often used. We demonstrate that such a thermal and compositional reservoir model is in a semi-explicit index-1 differential-algebraic form, and we briefly describe a gradient-based single-shooting algorithm for the solution of production optimization problems. We implement the algorithm in C/C++ using the software DUNE, the thermodynamic software ThermoLib, and the optimization software KNITRO. We present an example of optimal water flooding where the injected water has a higher temperature than the reservoir fluid.