欠饱和煤储层气水有效渗透率动态变化规律

Dynamic change law for gas-water effective permeability in undersaturated coal reservoirs

为准确量化正负效应对相渗曲线的影响,采用欠饱和物质平衡方程,将改进的PMG绝对渗透率模型与CPL相对渗透率模型在相同储层压力与含水饱和度下耦合,建立了考虑水侵的欠饱和煤储层有效渗透率动态预测模型,并分析了气水有效渗透率动态变化规律.研究表明:模型将有效渗透率统一为储层压力的函数,能很好反映煤储层正负效应,特别是基质收缩对于气相有效渗透率的改善作用;水侵引起净产水减少,导致含水饱和度降低变缓,抑制气相有效渗透率的升高与水相有效渗透率的下降,但对曲线形态影响微弱;若水侵量不再变化,定速水侵就转化为定量水侵.适当提高排水速度有助于降低水侵的影响.

An average gas-water effective permeability dynamic prediction model with water invasion in consideration was established to accurately quantify the influence of positive and negative effects on the relative permeability curves. In this framework, the improved PMG absolute permeability model and the improved CPL relative permeability model were comprehensively coupled under the same reservoir pressure and water saturation conditions through the material balance equation of undersaturated coalbed methane reservoirs. With the new model, the dynamic change law for gas-water effective permeability was analyzed. The model indicates that the effective permeability is expressed as a unary function of reservoir pressure. The results illustrate that the dynamic prediction model can accurately reflect both the positive and negative effects of coal reservoirs, especially the matrix shrinkage effect which could improve the effective permeability of gas. The water invasion could cause reduced net water production and slow water saturation decrease. Also it could inhibit the rise of gas effective permeability and the decrease of water effective permeability, but has little effect on the curve shape. When the water influx no longer changes, the constant speed water invasion converts into constant volume water invasion. Increasing the drainage speed properly is helpful for reducing the effects of water invasion.