Research Of Shale Gas Production Prediction Considering Fracture Propagation Patterns

Shale gas has the characteristics of self-generation,self-storage,low porosity and low permeability,not only exists in natural fractures called free gas,and also occurrence in the micro-nano pore called adsorbed gas,so that the shale gas percolation mechanism is very complex.For productivity prediction of shale gas fracturing horizontal well,the discrete fracture network seepage model is widely accepted,but due that horizontal well adopt the transformation model of staged fracturing and multiple clusters perforation,it will lead to the obvious stress shadow effect among the clusters in the reconstruction section and cause the distortion of adjacent hydraulic fractures.However,existing commercial numerical simulation software of reservoir usually assumes hydraulic fractures as discontinuities with the same width and permeability,without considering the deflection in hydraulic fracture extension.Therefore,it is very important to consider the effect of fracture propagation morphology on production prediction results.In this study,numerical simulation of production is carried out on the basis of fracture propagation model,the fracture propagation and production prediction coupling model is built to perform fracturing optimization design of shale gas reservoirs.Firstly,based on the fluidsolid coupling theory of hydraulic fracturing,the extended finite element method is utilized to study the influences of geomechanical parameters and fracturing parameters on fracture propagation pattern and induced stress fields in the process of synchronous fracturing,zipper fracturing and modified zipper fracturing.On this basis,the secondary development to ABAQUS software is carried out to derive the crack propagation trajectory and crack width,import which into the multi-field coupling numerical simulation software COMSOL Multiphysics as output.At the same time,the percolation mathematical model of fractured horizontal well under shale gas reservoir fracture system is established,and based on the finite element method,with the help of numerical simulation software COMSOL Multiphysics to solve it,contraposing crack propagation path of two different horizontal in defferent fracturing mode,shale gas production prediction and influence factors analysis is carried out from fracture mode,fracture cluster spacing,fracturing fluid displacement,the fracturing fluid viscosity and bottom hole flowing pressure and so on.This work of founding fracture propagation and productivity prediction coupling model is of fundamental importance to determine the optimal fracture spacing of horizontal Wells in different fracturing modes and field fracturing design.