Development of a Dual Media Full-Field Simulation Model to Optimize Injection/Production Strategy for Two Communicating Mature Carbonate Reservoirs

Abstract

Abstract An advanced integrated reservoir study has been performed for a giant mature oil field in Saudi Arabia. The field is composed of two naturally fractured reservoirs that are separated by a thick non reservoir formation. Same pressures have been recorded in both reservoirs since the start-up of production. Consequently, the two reservoirs are clearly in direct hydraulic communication. The geological data support that the communication is taking place through fractures swarms (sub-seismic faults) which affect the two reservoirs. A multidisciplinary approach was used to characterize and model the location of the fracture swarms by integration of available dynamic and static data. The resulting fracture grid of the simulation model combines diffuse fractures and fracture swarms. This paper discusses the ways to simulate these dual porosity – dual permeability (DPDP) systems that behave very differently, but still interact with each other. The lower reservoir is a tight matrix with diffuse fractures. Fracture density and capillary pressure control the oil recovery in this mixed wettability carbonate rock. Moreover, fracture swarms create reservoir anisotropy, which causes preferential fluid paths. In the upper reservoir, the matrix is very permeable with highly conductive strata. Due to the high matrix permeability, the dynamic contrast between the matrix and fracture media is low; thus, the fracture swarms only act as global permeability enhancers. This fracture multi-scale approach enabled us to history match the 5 millions active cells model (DPDP mode). The modeling accuracy was significantly improved by better representing the physics of the fracture-controlled system. It also provided new insight into the complex interactions between the two reservoirs through fracture swarms. The production history supports that these exchanges have been controlled by pressure regimes and fluids segregation in the fracture swarms. A better understanding of these communications led to a more optimized future injection/production development strategy.