基于连续拟稳定法的页岩气体积压裂水平井产量计算

水平井体积压裂是开发页岩气藏的关键技术。体积压裂后，未改造区域的流动为受微纳米孔隙介质控制的非线性渗流，而改造区域的流动则是由微米级裂缝网络控制的达西渗流。综合考虑页岩气藏体积压裂后的多尺度流动、页岩气解吸附、扩散等特点，建立了耦合未改造区域和改造区域流动的稳态产量计算模型；在此基础上，首次运用连续拟稳定法，考虑压力波不稳定扩散，结合物质平衡方程建立了页岩储层体积压裂水平井非稳态产量计算方法，并对页岩气体积压裂水平井非稳态产量的影响因素进行了分析。结果表明：基于连续拟稳定法建立的产量预测模型具有求解过程简单、计算速度快，与数值模拟结果吻合程度高的特点；页岩气的解吸效应主要影响生产中后期的产量；随着体积压裂区半径、压裂区渗透率、扩散系数、朗格缪尔体积的增大，页岩气井产能增大，且增加幅度逐渐减小；朗格缪尔压力对产量的影响较小。该方法为页岩气体积压裂水平井非稳态产量的计算提供了理论依据。

A productivity model of volume fractured horizontal wells in shale gas based on the continuous succession pseudo-steady state method

The volume fractured horizontal well is the key technology for developing shale gas reservoirs.After the stimulated reservoir volume is fractured,the gas flow in matrix is non-linear seepage controlled by the nano-scale pores,while the seepage in stimulated region is converted into Darcy flow controlled by the micro-scale fracture network.In this paper,the steady productivity model of volume fractured horizontal well was firstly established by comprehensively considering the multi-scale flowing states,shale gas desorption and diffusion,which coupled flows in matrix and stimulated region.On this basis,for the first time,a transient productivity calculation model combined with the material balance equation was obtained with the continuous succession pseudo-steady state method (SPSS),which considered the unstable propagation of pressure wave.And the horizontal well productivity prediction and factors analysis was carried out by using the SPSS.The results show that the model has the advantages of simple process,fast calculation speed and high agreement with numerical simulation results.Furthermore,it can be found that the seepage of shale gas is an unstable process.The pressure wave first reaches the boundary of the stimulated region,and then propagates to the reservoir boundary.During the production process,the desorption effect of shale gas is the key factor affecting the middle and late stage production of gas wells.With the increase of the radius and permeability of the stimulated region,the diffusion coefficient and Langmuir volume,the productivity of shale gas wells would increase,while the increasing rate would decrease.And the effect of Langmuir pressure on productivity is less.It is concluded that this method provides a theoretical basis for the calculation of transient productivity of shale gas fractured horizontal wells.