煤储层应力敏感性试验及其评价新方法

煤储层应力敏感性是影响煤层气井产能的关键地质因素，在煤层气井排采过程中如何降低或避免煤储层应力敏感性对渗透性的影响是值得考虑的问题。通过不同应力下煤储层渗透性试验，研究了有效应力作用下煤储层渗透率的变化规律；在对已有应力敏感性评价参数分析的基础上，提出了新的应力敏感性系数S₁与S₂，揭示了有效应力对煤储层渗透性的影响规律。研究结果表明:煤储层渗透率随有效应力的增加按负指数函数规律降低，在煤层气开发中煤储层表现出明显的应力敏感性；试验煤样应力敏感回归系数a为0.099~0.115 MPa-1，平均为0.108 MPa-1，应力敏感性系数S₁为0.383~0.436，平均为0.414，应力敏感性系数S₂为0.572~0.666，平均0.625；应力敏感性系数S₁与S₂具有整体性与唯一性，可以结合应力敏感回归系数a进行煤储层渗透率应力敏感性评价。 

Research on stress sensitivity of coal reservoir and a new method for its evaluation

The stress sensitivity of the coal reservoir is one of the key geological factors affecting coalbed methane well productivity, so how to reduce or avoid the effect of stress sensitivity on permeability is a question worth considering in CBM wells production process. Through the experiment of coal samples on permeability under different stress condition, the change law of permeability affected by effective stress has been studied. Based on the analysis of the pre-existing stress sensitivity evaluation parameters of coal reservoir, new stress sensitivity coefficients S1 and S2 were proposed, and the impact law of the effective stress on the permeability of coal reservoir was revealed. It is shown that the permeability of coal reservoir reduces with the increasing effective pressure by the negative exponential law and coal reservoir exhibits obvious stress sensitivity during the development of CBM wells. The permeability of coal reservoir cooperatively responses to coal strain under different stress condition. The stress sensitivity regression coefficient of tested coal samples is 0.099~0.115 MPa-1 with an average value of 0.108MPa-1, and is consistent with the well testing analysis results. The stress sensitivity coefficient S₁ is 0.383~0.436 with an average value of 0.414, and the stress sensitivity coefficient S₂ is 0.572~0.666 with an average value of 0.625. The defined stress sensitivity coefficients S₁ and S₂ in this paper exhibit integrality and uniqueness, and can be used to evaluate the coal reservoir stress sensitivity when combining with the stress sensitivity regression coefficient a.