非均质致密砂岩应力敏感性的定量表征

Quantitative analysis on stress sensitivity of heterogeneous tight sandstone

基于渗透率应力敏感实验研究非均质致密砂岩渗透率应力敏感性,根据颗粒Hertz接触变形法则,建立非均质致密砂岩毛管孔隙渗透率应力敏感定量表征模型,对孔隙度、渗透率和渗透率级差随有效应力变化规律进行了量化分析,并将理论计算结果与实验结果进行对比验证,从理论上对实验结果及规律进行了解释。结果表明,非均质致密砂岩的应力敏感性主要表现为渗透率应力敏感性,不同岩石渗透率随有效应力的变化具有不同步性,岩石渗透率越低,渗透率下降速度越快,非均质岩石渗透率下降速度介于岩石高渗透层与低渗透层渗透率下降速度之间;非均质岩石渗透率级差越大,渗透率应力敏感曲线越靠近岩石低渗透层渗透率应力敏感曲线,且渗透率级差随着有效应力的增大而不断增大。

The stress-dependent permeability in the heterogeneous tight sandstone has been studied based on the experiment of permeability stress sensitivity. Based on Hertz contact deformation principle,a capillary model for heterogeneous tight sandstone was established to characterize the stress sensitivity of capillary and porous media. The variation of porosity,permeability and permeability ratio under different effective stress was quantitatively analyzed. The theoretical calculation results were compared with the experimental ones as validation,and the experimental results were explained in theory. Research results show that the stress sensitivity of the heterogeneous tight sandstone is mainly presented as permeability stress sensitivity. Rock permeability varies with effective stress in different cores. The lower the rock permeability is,the faster the permeability declines. The permeability declining speed of the heterogeneous rock lies between those of the high permeability layer and the low permeability layer. When the permeability ratio increases,the stress-dependent permeability curves of heterogeneous rock are closer to that of the low permeability layer in rock. Heterogeneous tight sandstone permeability ratio becomes larger when effective stress increases.