Study On Unsteady Flow Of Vertical Fractured Gas Wells In Dual Porosity Media

In view of the geological characteristics of low porosity and low permeability in natural fractured gas reservoirs,hydraulic fracturing technology is usually used to effectively develop and utilize the reservoir.Vertical fractures are usually formed in the reservoir after fracturing.Therefore,it is of great significance to study the seepage mechanism of vertical fractured gas wells in dual porosity media.This paper starts with the nonlinearity of natural gas seepage equation and its semianalytical solution method,and then takes the seepage model of micro-compressible fluid in infinite dual media reservoir as an example to study the difference between the Warren-Root pseudo-steady interporosity flow model and the transient interporosity flow model of spherical matrix,and the influence of the matrix rock block geometry(spherical,cylindrical and layered)on the transient interporosity flow model.At the same time,a material balance equation that is more in line with the characteristics of dual media is established,which takes into account the effective compressibility of natural fractures and matrix rocks.On this basis,this paper establishes the transient interporosity flow model of spherical matrix to solve the unsteady flow problem of one-dimensional dual media gas reservoir.The nonlinear seepage partial differential equation is linearized by defining the pseudo pressure function of fracture and matrix respectively and the unified pseudo time function.The pressure distribution expressions of fracture system and matrix system are derived by using Laplace transform method.It is found that the pressure difference between the two systems is large in the early stage of seepage,and tends to be the same in the middle and late stage of seepage.The method to calculate the quantitative relationship between pseudo function and function is given with specific application examples.The unsteady flow problem of vertical fractured gas wells in rectangular closed dual media is studied by establishing the transient interporosity flow model of layered matrix.The expression of pressure distribution is derived by Laplace and Fourier integral transformation,and the early and late approximate results are compared with the analytical results.The treatment method of finite conductivity fracture is given,the typical dimensionless pressure and pressure derivative curve are drawn,and the flow segments are divided.According to the relationship between production and pressure,the expression of dimensionless production and cumulative production are derived,and the influence law of characteristic parameters and fracturing parameters is analyzed.The pressure and production performance of gas reservoirs are analyzed according to the specific application examples.The optimal fracture length and permeability can be determined under the premise of considering the field fracturing conditions and economic costs.Finally,the unsteady flow model of vertical fractured wells is applied to the production data analysis and performance prediction of multi-stage fractured horizontal wells.