An Approach For Analyzing And Predicting Production Performance Of Multiple-fractured Horizontal Gas Wells

The production conditions of gas wells would be changed by the adjustment of working system.Variable operating conditions would result in a notable change from the current constant-rate state to the subsequent constant-pressure state.These variations would change the inner boundary condition of the mathematical model of the well from the Dirichlet boundary condition to the Neumann boundary condition.Such a production system is defined as a two-stage production system in this paper,and such an inner boundary condition is defined as a two-stage inner boundary condition.Based on the construction and solution of intermediate function,the models of vertical gas well and vertical fracture gas well under the two-stage production system are established respectively.The results suggest that a high initial rate reduces the extents of both the constant-rate period and the total production life.However,the initial rate has no effect on the cumulative gas production when the production period is sufficiently long.Moreover,the initial rate should be appropriately adjusted to achieve the optimum cumulative gas production in a specific production period.The cumulative gas production can be effectively improved by establishing a lower limiting bottom-hole pressure.For multiple-fractured horizontal(MFH)gas wells under a two-stage inner boundary condition,the intermediate function for the MFH well is built by using the superposition of the intermediate function for a single fracture.Pseudo-functions,pointsource function,conductivity influence function and Laplace transform are used to solve the model semi-analytically.Finally,analysis of the characteristics of an MFH gas well under the two-stage condition is conducted.The results suggest that the initial rate should be adjusted based on the actual demand downstream and known fracture parameters,including the fracture half-length,fracture conductivity and fracture number.The limiting bottom-hole pressure,initial rate and fracture parameters affect the formulation and optimization of the rational production allocation and production system for MFH wells.Besides,on the basis of the derivation of the pseudo-functions that considering the effects of adsorbed gas and stress sensitivity,this model can be extended to a two-stage production system model for MFH wells in shale gas reservoirs.A semi-analytical model of MFH wells in multi-block heterogeneous gas reservoirs is established by the use of the source functions,Laplace boundary element method and Green's solution.To solve the problem that the combination of the pseudofunction approach with the material balance equation describing homogeneous gas reservoirs cannot be effectively linearize the nonlinearity in heterogeneous gas reservoirs,a multi-region material balance equation for heterogeneous gas reservoirs is derived.The influences of the crossflow coefficient,fracture conductivity,fracture halflength and storage ratio are analyzed.