页岩气致密储层渗流模型及压裂直井产能分析

页岩气储层中存在大量的纳微米孔隙，其中气体的流动规律不同于常规气藏. 文章考虑克努森扩散及解吸作用的影响，建立页岩气稳态条件下产能公式，利用渗流阻力法得到了页岩气储层压裂直井产能方程.结合生产实例，进行了数值模拟计算. 结果表明：当裂缝导流能力达到0.12μm²·cm 后，产气量增幅减小，由此对裂缝导流能力进行优化. 游离气产量占总产气量的85%～90%，游离气对总产气量贡献较大. 该模型为页岩气产能预测及开发指标优化提供了理论依据.

SEEPAGE MODELOF SHALE GAS RESERVOIR AND PRODUCTIVITY ANALYSIS OF FRACTURED VERTICAL WELLS

The flow mechanism in the shale reservoir involves the seepage, the diffusion and the desorption. A productivity formula for the shale gas is obtained under the stable condition with considerations of both the Knudsen diffusion and the desorption. With this formula, a productivity equation for the fractured vertical wells is established by the method of percolating resistance, with consideration both of the desorption and the diffusion. According to the formula derived and the production examples, the influence of the diffusion coefficient, the half-length of fractures and the fracture conductivity on the well gas productivity is studied. It is shown that the gas production increases with the increase of the diffusion efficiency. The greater the fracture conductivity, the larger the gas production will be. When the fracture conductivity adds up to 0.12 μm²·cm, the amplification of the gas production decreases significantly. The contribution of the free gas accounts for 85%～90%. So the free gas has a great contribution on the productivity. The model provides a theoretical basis for the production prediction and the optimization of the development index.