煤岩储层应力敏感性及其对气井开发的影响

Stress sensitivity of coal rock reservoir and its influence on gas well development

以沁水盆地3#煤为研究对象,对煤岩储层渗透率应力敏感性进行了实验研究,建立了以储层原地有效应力为初始点的渗透率应力敏感性评价方法。结果表明,该方法能够真实反映储层岩石应力状态,有效应力和无因次渗透率之间较好的符合二项式关系。利用扫描电镜和恒速压汞实验,分析了煤岩储层应力敏感性机理。孔隙大小和形态的改变对渗透率应力敏感影响较小,而孔喉大小和形态的改变以及微裂隙的开度决定了渗透率应力敏感程度。结合二项式方程,从理论上计算了渗透率应力敏感性对煤层气井产能的影响。计算结果表明,在气井井底附近煤岩储层中存在渗透率漏斗,距离井筒越近的储层,渗透率变化越大;在远离井筒的区域,渗透率变化较小。渗透率应力敏感性影响煤层气井产能,且初始渗透率越小,产能降低越严重。

The permeability stress sensitivity of Qinshui 3#coal rock reservoir is studied by experiments,and a new method to evaluate the permeability stress sensitivity is established on the basis of in-situ effective stress of reservoir rather than low effective stress.The results show that the method can correctly reflect reservoir rock stress state,the relationship between effective stress and dimensionless permeability in accordance with quadratic polynomial curve.The pore structure and fracture aperture tested by scanning electron microscope and constant rate controlled mercury penetration show that changes of porosity size and morphology is weakly affected by permeability stress sensitivity,while the throat and fracture aperture determine the degree of permeability stress sensitivity.The theoretical calculation shows that there exists a funnel of permeability near the bottom of gas well,the distance from wellbore is inversely correlated with permeability variation.Stress sensitivity of permeability has influence on coalbed methane gas deliverability,and the lower of initial,the more serious of deliverability reduce.