富黏土低渗透砂岩应力敏感性实验和微观变形机理

Stress sensitivity laboratory and microcosmic distortional mechanism of clay-rich and low permeability sandstone

为了评价大牛地气藏储层的渗透率应力敏感性,分析富黏土砂岩的微观变形机理,文中开展了大牛地气田富黏土低渗砂岩的渗透率应力敏感性实验。实验按2种方案进行:方案1按照部颁标准SY/T5358—2002进行;方案2是在几个固定的围压下,由孔隙流体压力(内压)变化产生对渗透率的变化。然后,运用3种评价方法对实验结果进行了对比分析,其中方法3最符合实际地层情况,最终得到此岩样应力敏感性中等偏弱的结果。在此基础上,文中还对该类富黏土砂岩在应力变化情况下的微观变形机理进行了分析,得出了黏土在孔隙压力减小的情况下,是由体积膨胀和颗粒分散运移2种原因对岩石渗透率产生影响的结论。

In order to evaluate the stress sensitivity of permeability for Daniudi gas reservoir and analyze the microcosmic deformation mechanism, this paper studied the stress sensitivity of clay-rich and low permeability sandstone and also conducted a series of experiments. The experiment was conducted by two different methods. In the first method, the ministerial standard SY/ T5358-2002 was used; In another method, the sensitivity by changing the pore-fluid pressure while keeping the confining pressure constant was obtained. Then, three kinds of methods were used to estimate the experiment results. After comparison, we find that the third method coincidences the actual situation best. At last, it comes to a conclusion that this kind of sandstones have strong sensitivity. On the basis of this experiment, the microcosmic deformation mechanism is analyzed, which shows that the clay in sandstone decreases the permeability by volume expansion and the scattered migration of grain.