Dynamics of Fracture-matrix Coupling during Shale Gas Production: Pore Compressibility and Molecular Transport Effects

摘要

Much work has been done to demonstrate an economical impact of various fluid transport mechanisms on the long term behavior of shale gas production. These studies were elementary level and focused on identifying a dominant mechanism of production. They did not consider, however, the interaction of the fractures with the shale matrices in detail. In the near wellbore environment the fracture is the crucial component of transport, whereas the matrix is the place for storage. In this paper, using a new in-house reservoir flow simulator, we introduce the nature of this interaction and show that the transport in the tight matrix can be induced by carefully designing the well completions and by operating under the optimum production conditions. The simulator accounts for a hydraulic fracture coupled to shale matrix with an anistropic apparent permeability field, which is stress-sensitive and includes the effects of molecular transport phenomena. The fracture has a dynamic conductivity with a simple nonlinear deformation rule reflecting proppant embedment effect on the conductivity. Using a sector model, we predict short-term cumulative production trends. The results indicate that design of horizontal wells with multiple fractures should take into account the geomechanical and diffusional resistances associated with the gas transport in the matrices. Further, in-series nature of the production indicates that changes in fracture conductivity beyond its threshold value has negligible effect on the production trends. Therefore, production optimization efforts should instead focus to considerations to improve the flow rates in the matrix.