Development of a Three-Dimensional Three-Phase Fully Coupled Numerical Simulator for Modeling Hydraulic Fracture Propagation in Tight Gas Reservoirs

摘要

Conventional fracture propagation models predict fracture geometry based on fracture fluid mechanics, rock mechanics, petrophysical properties, and analytical leak-off models. Reservoir flow simulators are then used to evaluate post-fracture well performances. This approach is called de-coupled modeling. It is a major challenge to couple these two processes, particularly when dealing with large amount of input data. Furthermore decoupled modeling is a time-intensive job that requires a coordinated effort from stimulation and reservoir engineers. This approach does not work in low-permeability reservoirs because the hydraulic fracture propagation is complex, fracture fluid leak-off is pressure/reservoir/fracture dependent, and there are changes in in-situ stress, permeability and porosity during and after fracturing. Therefore, a new model is needed to include all of these influences. This paper describes a three-dimensional, three-phase coupled numerical model which takes into consideration the mutual influence between dynamic fracture propagation and reservoir flow. The model is capable of fully simulating reservoir flow, fluid leak off, fracture propagation and resulted stress change through a stationary reservoir/stress grid system. The model uses a three-dimensional, three-phase finite difference reservoir flow simulator coupled with finite difference geomechanics model where both are applied on the same grid system. Using an iterative procedure, changes in pressure, in-situ stress and fracture propagation boundaries are determined during and after the fracture treatment. The model has been validated with the most recent available data. The results show that the model predicts fracture parameters accurately and match the history of injections and change in fracture /matrix area pressure/stress. Using this model, parametric studies can be made to quantify important factors affecting fracture and recovery processes. The new findings lead to better understandings of hydraulic fracturing and well performances in tight gas reservoirs.