不能用净应力评价低渗砂岩岩石应力敏感性

理论研究表明，低渗岩石由于存在微裂缝，净应力不等于有效应力。为了进一步论证净应力与有效应力的关系，开展了相关的实验研究，实验包含了老化处理和4个不同围压下的降内压实验，采用稳态法测定内压下降过程中各个压力点的渗透率值。实验结果表明：在不同围压下，净应力相等的点对应的渗透率值不相等，不能用净应力替代有效应力评价储层岩石的应力敏感性。此外，在低围压下渗透率的变化幅度较大；在高围压下，渗透率的变化幅度较小。最后，对实验岩样进行了储层岩石的应力敏感性评价，结果表明该低渗致密砂岩储层表现为中等应力敏感。

NET STRESS CAN NOT BE USED TO EVALUATE THE STRESS SENSITIVITY IN THE LOW-PERMEABILITY SANDSTONE

Theoretical study shows the net stress is not equal to the effective stress because of the existing microcracks in the low permeability sandstone.In order to demonstrate the relationship between net stress and effective stress，laboratory work is performed in this study.The experiment includes the aging treatment and four times test on decreasing inner pressure at different confining-stress.The permeability data at all pressure points in the process of decreasing inner pressure is obtained with the steady-state method.The results show that permeability is different for the equivalent net stress in the different confining-stress，which implies net stress cannot take the place of effective stress to evaluate the stress sensitivity.At low confining stress，the variation range of permeability is wider，while at high confining stress，it is narrower.In the end，the stress sensitivity evaluation on permeability is done and the results show that the stress sensitivity is moderate sensibility for the studied tight sandstone reservoir.