一种确定低渗透油气藏有效井网的新方法

A New Method to Establish Effective Well Pattern in Low Permeability Reservoir

低渗透油气藏经过压裂改造后,油气井周围渗流规律表现为非达西的椭圆流,确定这种复杂流动状态下的压力分布特征对于建立有效压力系统和制定科学的井网、井距至关重要。应用压降叠加原理和保角变换方法,建立了人工裂缝周围非达西椭圆流的压力梯度分布数学模型,对椭圆流长轴和短轴进行了求解,分析了低渗透油气藏建立有效井网的主控因素和部署对策。研究结果表明:随着流体流度的降低,椭圆流长短轴呈现指数式衰减,有效井网建立难度迅速增加;扩大压裂规模有助于建立井距方向的压力梯度,对排距方向压力梯度没有影响;对于那些受经济条件限制无法进行井网加密的油气藏,增加生产压差是建成有效注采压力系统的最主要途径。该方法准确、实用,对低渗油气藏有效井网的建立具有指导和实践意义。

Fracturing is generally applied to low permeability reservoir development and nonlinear elliptic flow occurs around the well.It is important to describe the pressure distribution contributed to build effective pressure system and then plan appropriate well spacing.With the theory of pressure drawdown superposition and conformal transformation,the distribution of pressure gradient for non-Darcy elliptic flow surrounding artificial fracture is derived.Meanwhile,the expressions of long-axis and short-axis are solved.Furthermore,the main factors affecting the well spacing and related solutions are analyzed.The result indicates that fracture scale,drawdown pressure and fluid mobility are the main factors.Studies have shown that effective pressure system is more difficulty to establish with decreasing mobility which will lead to rapid shortening of long-axis and short-axis and rapid decreases of well drainage distance.Expanding the fracturing scale can only increase the well spacing instead of row spacing;for those who neither establishing effective pressure system,nor having no possibility to infill considering the economic constrains,increasing production pressure gradient is the main way to build up an effective injection and production pressure system.One case is presented and the result reveals that the new method can be used to establish effective well pattern conveniently and practically.