Simulation study to investigate development options for a super-heavy oil reservoir

Abstract

A reservoir simulation study was performed on a heavy oil reservoir with the main objective of evaluating possible development options beyond the existing cold production method. The 206-acre area simulated - part of a significantly larger oil accumulation - lies about 3000 ft. ss. and has a gross thickness of 560 ft. The simulated area contains 120 MMSTB oil of 9° API gravity with in situ viscosity of 6,000 cp. Production began in 1992 with the reservoir being drained by one vertical well, one slanted well and one horizontal well. The simulation study was conducted in a systematic manner using two types of commercial reservoir simulators to minimize computational time. For history matching the cold production period and forecasting of cold production cases, a black oil simulator was used (ECLIPSE 100). A fairly satisfactory match of the production and pressure data was obtained which required an analytical aquifer to be attached to the northern part of the reservoir. For thermal EOR cases, the oil was simulated as a hydrocarbon consisting of three pseudo components. These cases were run using a thermal compositional simulator (ECLIPSE 300). Simulation results indicate oil recovery, for the area developed by the existing horizontal well and two new horizontal wells, to be as follows. For cold production, the oil recovery amounts to 13% of original-oil-in-place (OOIP). With cyclic steam injection, the recovery factor is slightly increased to 15% OOIP. However, with steam flooding -utilizing the new horizontal wells as injectors - the recovery factor is significantly increased to 22% OOIP. Steam flooding is evidently superior to cyclic steam injection primarily due to the fact that the reservoir is pressurized in the former EOR method and not in the latter, and to the fact that cyclic steam injection is more a near-wellbore thermal stimulation process as opposed to a more reservoir-wide heating process under steam flooding. Finally, with steam-propane injection (at a constant steam:propane mass ratio of 100:5), the oil recovery factor is further increased to 26% OOIP. Simulation results indicate this EOR method creates a more favorable distribution of heat in the reservoir, thus better sweep efficiency and reduction in produced water cut. Selection of development options to be implemented would depend on the economics of each case. Economic evaluation of the various cases has not been covered in the thesis and is best done by the operator of the field.