有效应力对煤储层不同方向渗透率影响的差异性

为探究有效应力对煤储层不同方向渗透率的影响差异,以鄂尔多斯盆地东缘柳林矿区南部4号煤层为研究对象,运用脉冲衰减克式渗透率测试方法,分析了不同有效应力条件下顺层渗透率及垂层渗透率变化规律及两者之间的相互关系。研究表明：煤储层不同方向渗透率随有效应力的增加均呈现幂指数降低的趋势,当有效应力为10MPa时,顺层渗透率及垂层渗透率均处于渗透率变化临界点,而且两者随有效应力的增大呈现线性相关的降低趋势,顺层渗透率与垂层渗透率比值为4∶1。通过对顺层及垂层的储层应力敏感性差异性研究,发现顺层及垂层裂隙压缩系数随有效应力压差的增大而减小,渗透率应力敏感性随有效应力差的增大而增大,顺层裂隙压缩系数、应力敏感性均小于垂层方向。通过煤储层不同方向的裂隙应力敏感性、渗透率应力敏感性对比分析,认为有效应力对煤储层不同方向渗透率的控制主要是由有效应力对煤基质裂隙的压缩存在空间差异性所造成的。

Study on the differences of effective stress on coal reservoirs permeability in different directions

In order to study the influence of effective stress on the permeability of coal reservoirs in different directions, this study takes the No. 4 coal seam in the south of Liulin mining area as the research object. And use the method of pulse attenuation gram permeability test to analyze the regional difference between the bedding permeability and the vertical layer permeability and the functional relationship between the two: the permeability of coal reservoirs in different directions shows a decreasing trend of power index exponent sign with the increase of effective stress. When the effective stress is 10MPa, the bedding permeability and the vertical layer permeability are at the critical point of permeability change, and the relationship between the two shows a linear correlation with the increase of effective stress. The ratio of the permeability of the bedding layer to the permeability of the vertical layer is 4∶1. By studying the differences in reservoir stress sensitivity to bedding layer and vertical layer, it is found that the compressive coefficient of the bedding layer and the vertical layer fracture decreases as the pressure difference of the effective stress increases, and the permeability stress sensitivity increases with the increase of the effective stress difference. The compressive coefficient and stress sensitivity of the bedding fracture are smaller than the vertical bedding direction. Through the fracture stress sensitivity and permeability stress sensitivity in different directions of coal reservoirs, it is believed that the reason why the effective stress controls the permeability of coal reservoirs in different directions is mainly due to the spatial difference in compression of coal matrix fissures by effective stress.