Non-uniform fracture aperture not only might affect initial reservoir fluids in place, but also production behavior. In addition, previous lab experiment has already demonstrated the importance of nonuniform aperture on permeability and residual oil distribution. This study investigates the impact of aperture averaging techniques on production performance of complex fracture networks in unconventional liquid reservoirs through fracture generation, unstructured gridding and reservoir simulation of hydraulically fractured horizontal wells.
First, complex fracture networks are generated from microseismic-constrained stochastic algorithms. We reduce uncertainties of natural fracture length, center, and strike distributions by incorporating outcrop analysis and microseismic event locations. Hydraulic fractures are generated by randomly connecting natural fractures and by honoring material balance equations. Then, stress-dependent nonuniform fracture aperture distributions were taken from previously CT-scanning experiment. Moreover, in order to evaluate production performance, nonuniform apertures are sampled from the lab-measured lognormal distributions and then populated along complex fracture networks. Nonuniform aperture is explicitly gridded up and discretized using unstructured grids for reservoir simulations. Finally, numerous aperture-averaging techniques are investigated considering whether or not to honor input fracture conductivity distributions.
Numerical simulations show that the same aperture distribution yields similar cumulative oil curves. With the increase of overburden stresses, the lab measured lognormal aperture peaks shift to the left. Correspondingly, it is observed decreased cumulative oil production. In addition, if fracture conductivity remains the same, the cubic law–based averaging approach yields the best production performance. If the fracture conductivity is not kept the same, the arithmetic averaging method provides us with the best production performance, which is followed by the base, geometric and harmonic cases.
This paper demonstrated how to simulate production performance of stress-dependent nonuniform aperture in complex fracture networks. The crucial impact of nonuniform fracture aperture and averaging techniques are highlighted through comparison with the uniform fracture aperture.