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

摘要

This paper examines the effects of matrix microfractures on effective matrix permeability of a dual-porosity medium. Ananalytical model is presented with composite matrix blocks consisting of a core where unconnected microfractures do notconsiderably 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 ofmacrofractures as in the conventional dual-porosity idealizations of fractured media. The paper investigates the effect ofmatrix-surface stimulation and demonstrates improved fluid transfer from the matrix medium to the fracture network due tomatrix microfractures. It is shown that matrix microfractures accelerate production by providing earlier and more effectivecontribution of matrix into flow rates. This contribution of the matrix due to microfractures cannot be simulated by enhancedmatrix permeability as the micro-fractured surface-layer of the matrix causes different flow characteristics than ahomogeneous (unfractured) matrix. The effect of the micro-fractured surface-layer of the matrix cannot be taken into accountby a triple-porosity model used to incorporate two sets of connected natural fractures or connected fractures and vugs either.