Well Test Analysis Method Of Oil-water Two-phase Flow For Volume Fractured Horizontal Well In Tight Oil Reservoir

Volume fractured horizontal well technology is an effective technique to enhance the oil recovery of tight oil reservoir.The seepage resistance between the reservoir and horizontal wellbore decreases after the fracture network formed around the horizontal wellbore by volume fracturing.Thus,it effectively improves the development efficiency of tight oil reservoirs.The fluids in the reservoir are in oil-water two phase flow condition for high water cut reservoir and water flooding reservoir.If the well test data is interpreted by single phase well test theory,deviations may occurs between the interpretation results and actual reservoir and fluid parameters.Therefore,based on the two-phase flow theory and method of mathematical physics,the two-phase flow well test analysis method for volume fractured horizontal well is formed.Firstly,an oil-water two-phase flow well test model was developed for water injection well in natural fractured oil reservoir.The saturation gradient and water imbibition were considered in the model.By combining the empirical imbibition formula and 1D B-L water displacement theory,the saturation model was developed and solved analytically by Laplace transform and inversion.Then the water saturation distribution at any time during water injection in naturally fractured reservoir can be obtained.By coupling the results with the pressure equations,the dimensionless bottom-hole pressure solution was solved through Laplace transform finite difference method.Features of the type curves for oil-water two-phase flow model were analyzed by drawing different type curves.On basis of the two-phase flow well test analysis of vertical water injection well,the oil-water two-phase flow well test model of multi-stage horizontal well was developed.The variation of water cut in reservoir and fracture system and the finite conductivity of hydraulic fracture were considered in the model.The model was solved semi-analytically by discretize the fractures into discrete fracture elements and the feature of the pressure curves was analyzed.Based on the investigations above,two well test models of oil-water two-phase flow for volume fractured horizontal well were developed.The hydraulic fractures were divided into main fractures and second fractures.The variation of water cut in reservoir and fracture system and the finite conductivity of hydraulic fracture were also considered in the model.The model was also solved semi-analytically by discretize the fracture into discrete fracture elements and the features of the pressure curves under different fracture network conditions were analyzed.Results from the study show that the shape of the pressure curves between the single phase and two-phase flow model is similar,but the curves move left and downward with the increase of the fluid mobility.There are two more stages,which are the fluid flow from second fracture into main fracture stage and the interference flow stage between the main fracture and second fracture,on the pressure curves by comparing the volume fractured horizontal well with the multi-stage horizontal well.The water cut in reservoir system of volume fractured horizontal well mainly has an effect on the formation pseudo-radial flow period and formation linear flow period,but has little effect on the fracture flow period.The water cut in fracture system mainly influences the fracture linear flow period and the period that fluid flow from second fractures into main fractures.With the increase of water cut in reservoir and fracture system,the curves move left and downward.This study provides guidance for the development and dynamic monitoring of volume fractured horizontal well in tight oil reservoir.