Research On The Productivity Prediction Model Of Production Wells In Tight Gas Reservoirs

As an important type of reservoir,tight gas reservoir is getting more and more attention and its little single well controlled reserves,low and rapidly decreasing and low recovery means the develop method used in conventional gas reservoir can not be adapted to tight gas reservoir.A calculation and prediction study for tight gas wells' off-take potential will be necessary for the design of reservoir's development.This paper uses the theory of vadose in gas reservoir to build equation of gas well's off-take potential for vertical well,slope and horizon well under the consideration of all production condition and gas production with water,which is based on the tight gas reservoir's geological character and the analysis of well testing and producing test.Numerical simulation is done and mathematical statistics method is used to study effect factors of each type of well's off-take potential and their influence degree.As a result,layer's thickness,fracture's quantity,pressure fracture's half-length,horizon interval length of horizon well,permeability,porosity and fracture conductivity are found to have obviously higher degree of influence in production than that of gas viscosity,starting pressure gradient and stress sensitivity.Beyond that,pressure fracture's half-length,fracture's quantity,fracture conductivity have the positive correlation with gas well's off-take potential;starting pressure gradient and stress sensitivity are opposite to the above factors.Based on the result of numerical simulation,multivariable and quadratic regression is used to build each well type's calculation model for gas well's off-take potential,and a software called ‘Calculation and Prediction for Tight Gas Reservoir Software' is coded by Visual Basic.The model is calculated both by analytical model and regression model,aiming to contrast two models' accuracy,and compared to simulation result,both model's error are under 15%,which means the model can be used.Calculation models for each type of gas well are built to predict their off-take potential for different production time,which is based on the actual geological data and production decline theory,and the model can provide reliably basis for the IPR study in the future for its permissible error which accours when compared with actual production history.