低渗气藏考虑非线性渗流特征的稳态产能方程

THE STEADY-STATE PRODUCTIVITY EQUATION CONSIDERING NONLINEAR PERCOLATION FEATURE IN LOW-PERMEABILITY GAS RESERVOIRS

低渗、致密砂岩气藏已逐渐成为勘探开发的热点,其储层特征和高含水特点导致了渗流机理不同于常规气藏,主要表现为:在近井区呈现为高速非达西渗流形式;在远井区由于启动压力梯度的影响呈现低速非达西渗流形式。因此,采用常规达西渗流条件下建立的产能方程评价单井产能必然存在误差。目前针对非线性渗流机理对开发的影响已有深入研究,但建立的模型大多是复杂不稳定渗流模型,现场实际应用不方便。为了弥补现有气藏工程理论的不足,从基本渗流方程出发,建立了考虑低速非达西渗流机理的直井稳态产能方程,与实际井测试数据进行了对比,并深入分析了低速非达西渗流机理在不同条件下对产能的影响程度。

Low permeability and dense sandstone gas reservoirs have become the focus of exploration and development. Its reservoir characteristics and high water cut feature lead to the fact that the percolation mechanism is different from that of conventional gas reservoirs, which are mainly manifested as following aspects: the high-speed non-Darcy percolation form is presented near well bore; the low-speed non-Darcy percolation form is presented far from borehole due to the impact of starting pressure gradient. Therefore, there must be errors existed by using the productivity equation to evaluate the productivity of single well, which is established under the condition of conventional Darcy flow. At present, the in-depth study has been conducted on the impact of non-linear flow mechanism to development, but most models established are the complex unstable flow ones, which are inconvenient in the worksite application. In order to make up the deficiency of the existing gas reservoir engineering theories, the study proceeded from the basic seepage equation, established the vertical wells steady-state productivity equation considering the low-speed non-Darcy flow mechanism, compared the result with actual well test data and took the in-depth analysis on influence degree of the low-speed non-Darcy flow mechanism to productivity under different conditions.