Research On Optimization Design Of Fractured Horizontal Wells In Low Permeability Gas Reservoirs

Fractured horizontal wells are now widely used as the key technology for the development of low permeability gas reservoirs efficiently in oil fields.However,some complex seepage phenomena such as starting pressure gradient existing in low permeability gas reservoirs lead to the nonlinear flowing of gas and the difficulty on productivity prediction.Therefore,it is of great significance to predict the productivity of fractured horizontal wells accurately and reasonably for the efficient development of low permeability gas reservoirs.First,this paper analyzes the problem on low initial production and rapid production decline of individual wells in the development of the Y gas reservoir.It is found that the starting pressure gradient has a great influence on the productivity of Y gas reservoir.Next,a partitioned physical model is built which meets the actual flow characteristics of the gas reservoir,where the gas seepage is divided into four flowing regions.Based on this,considering the starting pressure gradient,a mathematical model under the condition of the unsteady flowing is set up;then,using dimensionless treatment of parameters and the Laplace transform,the flowing equations in the four regions are coupled to obtain the productivity equation in the Laplace space,and the Stehfest numerical inversion is applied to obtain a semi-analytic solution to the productivity model.Furthermore,the productivity forecasting module is compiled.At last,the productivity-influencing factors are analyzed,ordered and optimized.Their impact orders are as follows from high to low: artificial fracture spacing,artificial fracture number,artificial fracture permeability,length of the horizontal section,half length of artificial fracture.Also,based on the different program values of the productivity influencing factors in this paper,the optimization combination of them is obtained under the premise of not considering the economic cost,realizing the productivity optimization of the Y gas reservoir to some extent.The research results in this paper have important and guiding significance for the efficient development of the Y gas reservoir using fractured horizontal wells.At the same time,they also have certain reference value for the development of similar low permeability gas reservoirs.