致密气藏压裂气井产能计算新方法

超低渗致密储层孔喉细小,属于微纳米孔,物性差,属于微纳米级流动,气体普遍存在复杂的非线性渗流效应,如滑脱效应、启动压力梯度及应力敏感效应。本文将超低渗致密气井的生产划分为三个阶段,早期段大裂缝的高速非达西流动,中期段反映裂缝边界控制椭圆达西渗流,晚期段反映基质的低渗非达西渗流。根据扰动椭圆的概念和等价的发展矩形的思想,引入新的拟压力函数,建立综合考虑气体滑脱效应、启动压力梯度、应力敏感效应共同影响下的气井压裂后产能预测模型,为超低渗致密气藏合理产能的求取提供理论依据。研究结果表明：在气井生产过程中,压敏效应对气井产能影响最大,其次是阈压效应,而滑脱效应仅在低压阶段起作用,并且影响较小；压敏效应较强的气藏,应减小气井生产压差。

A new productivity calculation method of fractured gas well in tight gas reservoir

Due to the ubiquitous nano-micro pore-throat scale in ultra-low permeability tight reservoirs, gas flow in porous media complies with nano-micro flow mechanism, which presents complex nonlinear flow characters, such as slippage effect, threshold pressure effect, and stress-sensitivity effect. In this paper, the production process of fractured vertical gas wells in ultra-low permeability tight reservoirs is divided into three stages, including high-velocity non-Darcy flow in large cracks in the early stage, elliptical Darcy flow controlled by the crack boundaries in the middle stage, and non-Darcy flow in the low permeability matrix in the later stage. Based on the concept of disturbance ellipse and equivalent rectangular, a new productivity calculation method for fractured vertical gas well in tight gas reservoirs is established on a new pseudo-pressure function, with the comprehensive effect of gas slippage effect, threshold pressure effect and the stress sensitivity effect taken into consideration. The new calculation method provides a theoretical basis for productivity calculation in tight gas reservoirs. The simulation results show that in the production process of fractured vertical gas wells, the pressure-sensitive effect has the most remarkable impact on gas well productivity, followed by threshold pressure effect. The slippage effect only has a relatively unconspicious influence in the low-pressure stage. Consequently, production pressure difference in gas reservoirs with strong pressure-sensitive effect should be reduced.