Study On Multi-scale Coupling Percolation Law Of Multi-fractured Horizontal Wells In Shale Gas Reservoirs

China is ushered in the shale gas revolution.However,the theoretical study of shale gas multi-scale seepage needs to be further strengthened.In this paper,through investigation and analysis,the insufficiencies that exist in the current research on transient flow of multi-fractured horizontal wells in shale gas reservoirs are concluded: the factors regarding to the micro-percolation mechanisms are not considered comprehensively and the assumption of artificial fractures' morphology after multi-fractureing in horizontal wells is too ideal.Aiming at the insufficiencies found,microscopic seepage mechanism models and macroscopic multi-stage fracturing horizontal well model that better fit the actual characteristics of shale gas reservoirs are established.This is of great significance for revealing the seepage law and pressure dynamic characteristics of shale gas at the bottom of multi-stage fracturing horizontal wells,and scientifically and efficiently using horizontal well fracturing to develop shale gas reservoirs.In terms of microscopic seepage model,the multiple migration mechanism in nanopores,the non-equilibrium adsorption and desorption of adsorbed gas,micropores and microfractures(which is a triple pore media.)are considered in this paper.A microscopic seepage mechanism model — — “ diffusion+ seepage in nanopore-micropore-microfracture” model is established innovatively.Then through dimensionless,Laplace transform,using the source function,delta function,etc.a unified form of point source solution is obtained.In terms of macro model,about well type: first study vertical wells,then horizontal wells;about flow form in fracturing fractures: first study infinite diversion,then finite diversion;finally,a seepage model for multi-stage fracturing horizontal wells in shale gas reservoirs is established in this paper.By coupling the solution of the microscopic seepage mechanism model to the macro model,the semi-analytical method of "discrete fracture + potential superposition" is used to find the solution of the model,and then MATLAB programming is used to draw a typical test curve.According to that,the gas flow in the fracturing horizontal well with limited diversion and multi-stage shale gas reservoir is divided into 9 stages.Finally,based on the typical well test curve,the influencing factors are analyzed.The research shows that the seepage effect in nanopores is so weak that it can hardly be considered,and the diffusion of the adsorbed gas cannot be ignored;fracture geometry distribution: fracture azimuth,fracture height and fracture spacing distribution have a great influence on the well test typical curve;compared with the traditional model,the model considered in this paper is more comprehensive and more in line with the actual development characteristics of shale gas reservoir.