Adaptability Evaluation Of Multistage Fracturing Horizontal Well In Tight Gas Reservoirs

In the past twenty years,the multi-stage fractured horizontal well has been widel y used to develop the tight gas reservoirs.However,multi-stage fractured horizontal wells increase costs and unreasonable fracture designs may lead to financial loss.Ther efore,the preliminary adaptability evaluation of multi-stage fractured horizontal wells in the gas reservoirs can greatly reduce the investment risk.This paper presents an an alytical model and a numerical simulation method for adaptability evaluation of multi-stage fractured horizontal wells.The main results are as follows:(1)A fracture model has been developed in a rectangle bounded gas reservoir.Based on the superposition principle,the pressure at any point in the formation can be obtained for multiple fractured well.The coefficient matrix of pressure and producti on rate can be sloved by using Gaussian elimination method.The pressure of finite conductivity fracture can be obtained by adding a conductivity influence function.(2)This paper discusses the influence of fracture conductivity,formation permea bility,flow area,fracture damage and pressure difference on the production rate.It is shown that the fluid flow area is the main factor for the production rate.In the same pr oduction time,the bigger the formation permeability is,the bigger the flow area.Mea nwhile,the reserves,production pressure,fracture conductivity and the skin of fractur e have little affection on the fluid area and well production.(3)The fractured horizontal wells have large advantages than the fractured vertic al well.Multi-stage fractured horizontal wells are an effective way to develop ultra tig ht gas reservoirs.Reasonable well spacing is also very important.Well spacing is too 1 arge,the recovery will be very low;well spacing is too small,it will be not economic.(4)In a low permeability reservoir,the pressure propagation is not instantaneous reach infinity,but presents a moving boundary gradually spread outward.Under the s ame conditions of pressure gradient,the maximum extension length of theminor axis of the ellipse is π/2 times than ordinary vertical wells.According elliptical theory,the maximum distance of short-axis determines the fracture spacing;the maximum distan ce of long-axis determines the row distance of the horizontal well.(5)For the presence of pressure gradient in the gas reservoir,the analytical mod el can be used for adaptive assessment;semi-empirical model based on numerical si mulations can be used to assess the adaption of multi-stage fractured horizontal well f or the gas reservoir without staring pressure gradient.Two field examples demonstrat e the application of the new methods.