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

Abstract

Abstract This paper examines the effects of matrix microfractures on effective matrix permeability of a dual-porosity medium. An analytical model is presented with composite matrix blocks consisting of a core where unconnected microfractures do not considerably contribute 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. The paper investigates the effect of matrix-surface stimulation and demonstrates improved fluid transfer from the matrix medium to the fracture network due to matrix microfractures. It is shown that matrix microfractures accelerate production by providing earlier and more effective contribution of matrix into flow rates. This contribution of the matrix due to microfractures cannot be simulated by enhanced matrix permeability as the micro-fractured surface-layer of the matrix causes different flow characteristics than a homogeneous (unfractured) matrix. The effect of the micro-fractured 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 either.