基于可视缝宽测量的储层应力敏感性评价新方法

New Evaluation Method of Permeability Stress Sensitivity Based on Visual Fracture Aperture Measurement

储层应力敏感性在储层保护、产能预测、油气田开发方案制定等方面有着重要的研究意义。利用加载岩石微观图像分析装置,研究了致密碳酸盐岩在不同围压下的裂缝宽度和渗透率分布特征及变化规律,结合常规的储层应力敏感性评价实验,探讨了储层应力敏感性的裂缝宽度特征值。研究表明：①裂缝压缩过程具有自相似性,裂缝宽度在围压（0~20 MPa）增加后仍呈正态分布;②窄裂缝比宽裂缝对围压变化更敏感,但宽裂缝绝对变化量大;③宽裂缝宽度控制并反映了致密岩石渗透率的整体变化特征,岩样90%的渗透率由仅占10%的宽裂缝所决定;④裂缝宽度累积分布曲线上纵坐标为90%所对应的缝宽,可以用来评价裂缝性致密储层的应力敏感性,同常规应力敏感性评价结果较为一致。

Reservoir stress sensitivity evaluation is an important tool in reservoirs protection,production forecast,and development program decision.Because the fracture surface is not smooth,the fracture width is not a constant value along the fracture,and it can change with the wellbore pressure.It is still debatable which width value property of facture variati on has been argument.To solve this problem,the microscopic image analysis device for loading rocks has been used.The distribution and variation of facture width and permeability has been investigated at different confining pressures.In combination with conventional experimental evaluation of reservoir stress sensitivity,we discuss the eigenvalues of fracture aperture.The results show that aperture distribution would keep a normal distribution when the confining pressure increase between 0MPa and 20MPa,and the process of fracture compaction shows a property of self-similarity.The narrow aperture is more sensitive to the confining pressure than that wide one,but the changed range for the absolute value of wide aperture is lager than that of narrow one.The wider fracture aperture constrains the variation of fracture.Permeability of 90% is determined by only 10% of the larger fracture aperture in the fractured rock samples.The fracture aperture corresponding to 90% at ordinate axis in the aperture accumulation distribution curve can be used to evaluate the stress sensitivity of fracture tight reservoir.The new results are consistent with conventional methods,which verify the selected eigenvalue is validity.