Innovation of Numerical Simulation in Tight and Fractured Reservoirs for Better Offshore Development Strategy

Abstract It is well known that the oil and gas flow in the tight and fractured reservoir often deviates from conventional behaviors. Regular numerical simulation methods often find it difficult to represent the abnormal drainage area and heterogeneity in such formations, which makes the development strategy less reliable. In our study, we used pressure gradient threshold (PGT) to define a non-linear flow behavior in the matrix, and we used embedded discrete fracture model (EDFM) to represent the flow behavior in the natural fractures. This combination matches well with the testing result, and it provides a reliable approach for development strategy of production and injections in the field. Field-X is an offshore condensate gas field containing over 200 BSCM of natural gas and 200 MSCM of oil in place. Though field-X is the largest condensate reservoir in East China, the formation is tight and highly fractured. Previous studies show that in field-X, the actual drainage area from individual well is significantly smaller than the simulation predictions, while regular dual porosity dual permeability (DPDK) method cannot fully represent the flow impact from the natural fractures. In this study, we took innovative simulation approaches to solve those two problems. We incorporated non-linear flow equation in the matrix flow, where PGT definition were calibrated to match the well testing pressure build-up results. We also built a natural fracture model and converted it to EDFM for reservoir simulation to represent the true impact from those fractures. The combination of the two approaches allows us to properly simulate the flow in a heterogeneous reservoir environment in Field-X, so that systematic development strategy, including well pattern, injection preference, etc., can be better optimized. This technical innovation has been put into the actual operations of Field-X. In the development phase-I, 65 well site has been confirmed with this approach, 41 of which were drilled, completed and put to production, contributing approximately 4000 ton of oil and 3 MSCM of gas on daily bases, which is 50% higher than the original development planning.