Theoretical Research On Unstable Seepage Of Horizontal Wells In Low-permeability Fractured Gas Reservoirs

On the basis of fractured reservoir research results,focusing on the stress sensitivity and starting pressure gradient effect under consideration,the integrated use of modern methods of mathematical physics,fluid mechanics,computer programming and other related knowledge,systematic study of a series of seepage problem by using the integral transform method and Green function method.Including the unstable seepage model is established for horizontal well,horizontal well fracturing,using the method of variable substitution elimination equation of nonlinear characteristics of Laplace transform and orthogonal transform calculated by the solution of the model,draw the corresponding typical curves,and further explores the influence of wellbore storage coefficient,flow coefficient,skin effect and other parameters on the curve typical pressure,provide a theoretical basis for well testing of fractured gas reservoir.Through the study of this paper,the following conclusions and understanding are obtained.(1)Through the literature investigation and summary of the development practice of fractured gas reservoirs at home and abroad,the effects of stress sensitivity and starting pressure gradient on the seepage of fractured gas reservoir are deeply understood and recognized,and the characteristic parameters of natural fractures,the index of permeability variation and the movement equation of low speed non Darcy percolation in the fractured gas reservoir are determined.(2)Based on the equation of permeability variation index and low velocity non Darcy seepage flow,the mathematical model of unsteady seepage in horizontal well and fractured horizontal well is established under the influence of starting pressure gradient and stress sensitive effect.The analytical solution of the mathematical model is obtained by Pedrosa variable substitution and mathematical physics method,and the corresponding pressure response of each analytical solution is drawn.It should be dynamic curve.(3)According to the morphological characteristics of the dynamic response curve,the dynamic curve of horizontal well pressure in fractured gas reservoir is divided into 7 stages:well bore storage effect stage,transition flow stage,wellbore radial flow stage,fracture linear flow stage,fracture radial flow stage,matrix crack channeling stage,and gas reservoir radial flow stage.(4)According to the morphological characteristics of the dynamic response of the pressure response,the dynamic curve of the horizontal well pressure response in fractured gas reservoir is divided into 8 stages:the well bore storage effect stage,the transition flow stage,the pressure crack linear flow stage,the fracture seam radial flow stage,the fracture linear flow stage,the fracture radial flow stage,the matrix crack channeling stage and the gas reservoir radial flow stage.(5)Based on the established unstable seepage model and the corresponding analytical solution,the influence of the parameters of the wellbore reservoir coefficient,the skin coefficient,the stress sensitivity coefficient and the starting pressure gradient on the dynamic response curve of the horizontal well and the fractured horizontal well is analyzed.