Analysis Of The Expansion Law And Influencing Factors Of Drainage Radius In Tight Gas Reservoirs

Due to the extremely-low permeability of tight gas reservoirs,the wells need to be hydraulically fractured before production,and most field engineers treat the fractured zone as the drainage area.However,the phenomenon of weak fluid supply from the outer zone to the drainage area is observed in tight gas reservoirs,which caused the problem of single well control reserves increasing and uncertainty.To solve this problem,based on the theory of seepage and well test,the expansion low of drainage radius in tight gas reservoir is studied.First,an additional skin factor is introduced at the interface of the two zones to characterize the weak fluid supply ability.Then,a novel radial composite fractured well model is developed by considering weak fluid supply,stress-sensitivity effects,and finite-conductivity fractures.The reservoir model is solved by the perturbation transformation,point source integration method,Laplace transform,and numerical inversion.While the fracture model is solved by fracture discretization and superposition principle.Finally,the bottom-hole pressure is obtained.Based on the model pressure solution,the theoretical calculation formula of drainage radius in tight gas reservoir is obtained by the derivation method.Combining pressure rate coupling analysis method,a set of calculation methods suitable for drainage radius in tight gas reservoir is proposed.The expansion low of rainage radius in tight gas reservoir is also investigated.Results show that the additional skin factor causes the curves merge and uplift at the interface of the supply zone and the fractured zone,which is called pseudo-boundary effects.In addition,the increase of the mobility ratio,the storage capacity ratio and the stress sensitive modulus of the reservoir makes the pseudo-boundary effect more obvious.Based on the theoretical calculation formula,in the vertically fractured well and the multistage fractured horizontal well models,there is a linear relationship between the drainage radius square difference and the production time difference in the supply zone.The drainage radius main effect factors of the vertically fractured well are the radius of the inner zone,the storage capacity ratio,the mobility ratio and the additional skin factor.While for the multi-stage fractured horizontal well are the radius of the inner zone,the storage capacity ratio and the additional skin factor.Finally,based on the pressure rate coupling analysis method and calculated formula,the expansion laws of drainage radius for the actual tight gas wells are investigated,indicating that the study is practical.