超低渗透砂岩储层应力敏感性实验

采用全自动岩心驱替系统，应用双重有效应力理论对鄂尔多斯盆三叠系超低渗露头全直径岩心进行应力敏感性评价。实验结果表明：在使用变内压定围压方法进行实验时，由于压力传感器和压差传感器在较大压力变化范围内存在零点漂移问题，会导致完全错误的实验结果，进一步通过变围压定内压的方法对超低渗渗透储层进行了应力敏感性评价。研究结果表明，岩石被压缩的过程可分为微裂缝闭合阶段与岩石受压缩阶段两个阶段。前一阶段由于微裂缝闭合，渗透率快速下降，降幅达20%左右；微裂缝闭合之后，岩心继续被压缩，渗透率下降变缓，降幅为5%左右，即在地层有效应力条件下，超低渗透储层应力敏感性很弱，应力敏感性对低渗储层的产量影响不大。

An experimental study on stress-dependent sensitivity of ultra-low permeability sandstone reservoirs

According to the theory of dual effective stress,the present paper studied the stress-dependent sensitivity of ultra-low permeability sandstone cores(full diameter) sampled from the Triassic outcrop of the Ordos Basin by using an automatic core displacement system.The experimental results indicated that when the method with variable internal pressure but constant peripheral pressure was used,the outcome went against common knowledge due to the zero drift of both the pressure sensor and the differential pressure sensor caused by broad variations in fluid pressure.So the method with constant internal pressure but variable peripheral pressure was adopted in the test,and the outcome demonstrated that the process of rock deformation could be divided into two phases,namely the microcrack closure phase and the rock compression phase.During the first phase,the permeability reduced dramatically by 20% due to the closure of microcracks,while in the second phase,the permeability decreased slowly by 5% with the increase of peripheral pressure that keeps compressing rocks.Therefore,the paper proposed that the stress-dependent sensitivity of ultra-low permeability reservoirs under the in-situ stress was weak and its effect on the productivity of low permeability reservoirs was negligible.