Forties CO2 IOR Evaluation Integrating Finite Difference and Streamline Simulation Techniques

Abstract

Abstract In September 2000 the Forties Field celebrated 25 years of production. Recovery up to this point is approximately 60% of the original oil in place. The field contains undersaturated oil and is being developed under waterflood. A screening study of Increased Oil Recovery (IOR) options highlighted CO2 injection as technically feasible, suggesting an additional recovery of in the range 5-10% of the initial oil in place (STOIIP), subject to further work on the investment economics of the project and corporate sanction. This paper describes the study of the CO2 injection scheme with a focus on the reservoir simulation workflow. Various techniques for evaluating the full field benefits of IOR schemes can be used including the Todd and Longstaff approach1 or a coarsely gridded conventional compositional reservoir simulation model. The evaluation presented in this paper builds upon a technique that incorporates detailed conventional simulation results into a full field streamline front-tracking simulation. This method was originally developed by Arco and has been successfully applied in several Alaskan oil fields2. The technique captures the complex physics of the IOR process through fine scale, 3D, compositional, finite difference simulations of ‘type’ sections of the reservoir (the original method used 2D simulations). Results from these simulations are then used to calibrate ‘recovery’ curves that capture characteristics of oil mobilisation and returned solvent volumes as a function of gas injected. The calibrated curves representing gas injection response are then applied as tracers using streamline front tracking simulation to scale up to full field response.