Pressure And Rate Analysis Method For Well Intercepting Multiple Fractures In Multilayered Tight Gas Reservoir

After separate layer fracturing and refracturing of multilayer tight gas reservoirs,new and old fractures,hydraulic fractures,and natural fractures form the fracture system with different fracture lengths and fracture conductivity.Focusing on complex flow problems such as multi-fracture systems and multiphase flow in separate layer fractured wells of tight gas reservoirs,this work presents the pressure and rate transient analysis methods.It is of great significance to understand the flow of separate layer fracturing wells and further improve the development effectiveness in tight gas reservoirs.First,considering the differences in fracture length and conductivity between new and old fractures in tight gas reservoirs,the fracture flow model in tight gas reservoirs is established using the boundary element method.Based on the point source function and the pressure superposition principle,the reservoir flow model is established.A well test model is finally proposed after coupling the fracture flow model and the reservoir flow model and considering the interference from adjacent wells.The type curves are developed.The pressure transient analysis method for diagnosing the number of fractures and the interference degree of adjacent wells is proposed.The results show that the uneven fracture conductivity of new and old fractures affects the bilinear flow and linear flow regimes.The pressure and pressure derivative curves go downward,and the flow ability is stronger with more fractures and adjacent wells.The interference of adjacent wells mainly affects the flow regimes between wellbore storage and system radial flow regime.If the production ratio of test well to all wells equals δ,the pressure derivative value at the radial flow regime is 0.5 δ.The application of well test analysis example shows that this method is feasible.Secondly,in view of the difference in fracture length and conductivity of each layer after hydraulic fracturing in the multilayer tight gas reservoir,the fracture flow model with non-uniform conductivity is established based on the principle of mass conservation and Darcy’s law,and the reservoir flow model is established based on the Green source function.The well test model of separate layer fractured well in multilayer gas reservoirs considering the uneven fracture conductivity is presented after coupling the fracture and reservoir flow model,and is solved by the boundary element method and pressure superposition principle.The type curves for pressure and rate transient analysis are developed,and the pressure and rate transient analysis methods are further presented.The results show that the bilinear flow regime and the pressure derivative results of multilayer fracturing wells differ from single-layer fracturing wells.The decrease of fracture conductivity at the fracture tip causes the flow resistance within the fracture,which affects the linear flow regime,and makes it difficult to identify.If the fracture length difference between layers or the non-uniformity of fracture conductivity is not considered,the fracture conductivity will be overestimated.The feasibility and applicability of this method are demonstrated by analyzing the field examples.Finally,considering the stress sensitivity and gas-water co-production in tight gas reservoirs,a two-phase well test model for separate layer fractured wells in tight gas reservoirs is obtained based on the mass conservation equations of gas and water phases.The type curves are developed and the sensitivity analysis is conducted.Under the condition of two-phase flow,the upward amplitude of the pressure derivative curve with a start-up pressure gradient is much smaller than that of single-phase flow,indicating that the impact of the start-up pressure gradient on the pressure response is reduced after water breakthrough in the gas well.When the number of natural fractures connecting the upper and lower layers increases,the pressure derivative curve moves downward,and the flow resistance of the reservoir decreases.As the water production in the gas well increases,the pressure derivative curve gradually moves upward,and the flow resistance in the fracture system of the reservoir increases.The feasibility and applicability of this method are demonstrated by analyzing the field examples.