Study On Productivity And Numerical Simulation Of Fractured Horizontal Well In Low Permeability Gas Reservoir At Sea

Though there is a huge potential in the tight gas resource in marine,it is difficult to develop by conventional vertical wells because the poor properties and low reserve abundance in this type of reservoir.Recent years,a technology of combining horizontal well(HW)drilling and hydraulically fracturing has been developed to improve well production performance.It makes great contribution in the commercial development of marine tight gas reservoirs.However,many engineering problems still exist,such as uncertainty in influence factors,difficulties of productivity evaluation caused by nonlinear flowing mechanisms.As a result,it is difficult for petroleum engineers to evaluate the gas well productivity,optimize fracture parameters and conduct reasonable managed drawdown of gas well.In conclusion,based on the production performance analysis of horizontal wells in gas field in the East China Sea,a steady-state productivity evaluating model is established by coupling reservoir and fracture flowing systems.In addition,various nonlinear flowing mechanisms including slippage effect,non-Darcy flow and stress sensitivity were taken into account.Correspondingly,the calculation software is developed by programming.Finally,the research results were incorporated into commercial numerical simulation to evaluate the productivity and future performance of HWs in tight gas field.The specific contents are as follows:(1)Combined with the basic theory of potential,superposition principle and fluid mechanics,a fundamental steady productivity model is established by coupling reservoir and fracture flowing systems,which is twofold:a)an analytical expression in reservoir flowing system is obtained by applying Fourier sine inverse transformation;b)an analytical expression in fracture flowing system is obtained by introducing multi-source function.A corresponding semi-analytical solution is developed by discretizing fracture panel into fracture segments and establishing linear equations.(2)Several nonlinear flowing mechanisms are considered including slippage effect in tight reservoir,non-Darcy flow effect in fracture,and stress-sensitivity conductivity of fracture.The resulting nonlinear problem is regarded as linear problem by combing special dimension transformation and the former fundamental model.The productivity index could then be obtained by solving the resulting nonlinear equations on the basis of the adaptive iterative algorithms.(3)On the basis of productivity evaluation model,various results can be obtained.The influence factors including engineering factors and geology factors are analyzed and detected in detail.As the same time,the sensitivity analysis is determined by using orthogonal tests.and the controlling factors are listed in the order of their impact degrees as follows:fracturing penetration radio,fracture length and fracture conductivity.As a result,the focus of fracturing treatment should be put on increasing fracture length and decreasing well spacing to enhance productivity of single well.(4)The other focus of this paper is put on integrating our productivity model with reservoir numerical simulation.A numerical reservoir model is established by using the characterized parameters from gas field.The full-cycle production performances are predicted under different scenarios.The 20-th year cumulative production is regarded as target function to optimize fracture parameters.The synthetic case results are in good agreement with that of our model.