Effect of Discontinuous Microfractures on Ultratight Matrix Permeability of a Dual-Porosity Medium

Abstract

Summary This paper examines the effects of matrix microfractures on the effective matrix permeability of a dual-porosity medium. An analytical model is presented, with composite matrix blocks consisting of a core in which unconnected microfractures do not contribute considerably to flow capacity and a surface layer where the microfractures connected to the matrix surface (resembling wormholes) cause a stimulation effect. The composite matrix flow is coupled with the flow in a network of macrofractures, as in the conventional dual-porosity idealizations of fractured media. This paper investigates the effect of matrix-surface stimulation and demonstrates improved fluid transfer from the matrix medium to the fracture network because of matrix microfractures. It is shown that matrix microfractures accelerate production by providing earlier and more-effective contribution of the matrix into flow rates. This contribution of the matrix because of microfractures cannot be simulated by enhanced matrix permeability because the microfractured surface layer of the matrix causes flow characteristics different from those of a homogeneous (unfractured) matrix. The effect of the microfractured surface layer of the matrix cannot be taken into account by a triple-porosity model used to incorporate two sets of connected natural fractures or connected fractures and vugs.