2008 · 101 citations · 10 references
EngineeringGeological EngineeringPetroleum EngineeringReservoir EngineeringReservoir SimulationSubsurface Fluid FlowFracture GeometryFracture MechanicsFracture PropagationFractured Reservoir FlowFractured Reservoir SimulationShale Gas ReservoirsDarcy Flow ModelingFracture PermeabilityFracture SpacingGas StorageGas Storage MechanismsMatrix DiffusionMatrix PermeabilityStress-dependent Permeability
Gas shale production is highly variable due to heterogeneity and microfabric of matrix and fracture networks, with Darcy flow through fractures often considered the main control and matrix primarily serving as storage. The study develops a 2‑dimensional numerical model to evaluate the relative influence of fracture spacing and matrix diffusion/flow on gas shale production. The model incorporates experimentally derived diffusion rates and stress‑dependent fracture permeability to simulate gas flow through both matrix and fractures, enabling comparison with measured production histories. Simulations indicate that, across a wide range of fracture and matrix permeabilities, reservoir productivity is governed by matrix diffusion rates.
Abstract The heterogeneity and complexity of gas shales cause substantial and often inexplicable variability in the production histories of gas wells. A major factor contributing to this variability is the microfabric of the matrix and the fracture network of the reservoir. It is widely postulated, although not proven, that the gas production from shales is controlled principally by Darcy flow through the fracture system and the matrix is considered important principally for gas storage. In order to gain insight and test the relative importance of fracture spacing and matrix diffusion/flow on the production of gas shales, we have developed a 2-dimensional numerical simulation model, which considers the flow of gas through both the shale matrices and the fractures for varying fabrics utilising experimental data obtained from a variety of important gas shales. The results of initial, constant parameter, numerical simulations showed that for a wide range of relative fracture permeability, matrix permeability/diffusivity and fracture spacing, the productivity of a gas shale reservoir is dependent on matrix diffusion rates. The diffusion rates and stress dependent fracture permeability data when integrated into the numerical simulator can be tested against measured production histories leading to more accurate production forecasts of new reservoirs and optimisation of field design.
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