Development of a Fully Coupled Two-phase Flow Based Capacitance Resistance Model CRM

Abstract

Abstract The capacitance resistance model (CRM) has become a popular complement to real time reservoir analysis and improved oil recovery in water and CO2 floods. However, the current CRM model is based on a material balance of the total fluid and only the pressure propagation equation is considered. Saturation changes are also important, especially when the water cut is small. To overcome this limitation, this paper proposes a coupled CRM model based on two-phase flow by incorporating an oil material balance and fractional flow theories. In the coupled CRM model, we construct material balances on both total fluid and oil. Pressure and saturation equations are updated at each time step to account for changes of total mobility. By semi-analytically coupling the pressure and saturation in a producer-based control volume and using constrained multivariate nonlinear regression, the new coupled model can quantify the inter-well connection as well as the oil saturation. As a result, the coupled CRM model can be applied to the whole time frame of water and gas floods, not limited to late time (large water cut) cases as was the current CRM model. This new CRM model is validated in heterogeneous synthetic fields using a conventional reservoir simulator. Case studies show that the saturation profile from the coupled CRM model matches very well with the simulation results. The connectivities obtained from the coupled CRM model correspond well with the field geology and the time constant for each producer is also changing reasonably with the total mobility. Validation of both total production and oil production rates showed that relative errors are very small. With estimated parameters from a waterflood, the model found an optimal injection strategy to maximize the field total oil production. By incorporating the saturation variations to model two-phase flow, the coupled CRM model successfully overcomes the limitation of the previous version. It is able to extend the CRM model from mature water floods to immature water floods, which makes the CRM model more adaptable to different field cases. The coupled CRM model also improves the quality of the prediction of the oil rate significantly, especially for immature water floods. This work can lead to a more informed workflow of optimizing injection scheme, and serve the goal of improving ultimate oil recovery.