低渗气藏特殊渗流机理及稳定产能预测方法

摘要

The low permeability gas pools, different from conventional gas reservoirs, are characterized by poor reservoir physical properties and high water saturation, thus its seepage mechanism is even more complex. This paper sets forth in detail the special seepage mechanism of low permeability gas pools based on low permeability reservoirs. Meanwhile, in line with inadequate consideration factors for productivity forecast of low permeability gas pools and inaccuracy of the result of productivity assessment, this paper inferred a general equation for prediction of stable gas productivity, according to gas pool productivity equation under stable seepage conditions and activating pressure gradient model, and taking into full consideration the gas slippage effect and multiple non-linear effects like low-rate non-darcy effect, high-rate non-darcy effect, pressure sensitivity effect, in combination with seepage mechanic fundamentals. The result shows that the low-rate non-darcy effect, high-rate non-darcy effect and pressure sensitivity effect of low permeability gas pool all cause the gas pool productivity to become smaller. If these effects were neglected, then optimistic assessment would be made on productivity. Among which, the activating pressure gradient and pressure sensitivity coefifcient (particularly the anomalous high pressure reservoir) have a signiifcant effect on gas well productivity. The slippage factor plays a second role, and the high-rate non-darcy effect has the least effect. The examples conifrmed the correctness of the productivity model, which can be used for actual ifeld development work.%不同于常规气藏，低渗气藏由于其储层物性差、含水饱和度高的特点，其渗流机理更为复杂。以低渗储层为基础，对低渗气藏特殊渗流机理进行详细阐述；同时针对目前低渗气藏产能预测考虑因素不全、产能评价结果不够准确的问题，在拟启动压力梯度模型的基础上，依据稳态渗流条件下的气藏产能方程，综合考虑气体滑脱效应、低速非达西、高速非达西、压敏效应等多重非线性效应，结合渗流力学基本原理，推导了通用气体稳定产能预测方程，并进行参数敏感性分析。结果表明：低渗气藏的低速非达西效应、高速非达西效应、压敏效应都会使气藏产能变小；如果忽略其影响，将会造成对产能的乐观评价；其中启动压力梯度和压敏系数（尤其是异常高压储层）对气井产能影响显著，滑脱因子次之，高速非达西效应影响较小。通过实例验证了产能模型的正确性，可以用于指导现场实际开发。