有效应力作用下岩石渗透性和电性响应特征

Permeability and Electrical Response Characteristics of Rocks Under Effective Stress

针对砂岩储层有效应力变化对渗透率和地层因素的影响,通过分析不同形状孔喉在有效应力作用下的形变规律,推导出有效应力变化对配位数z、孔喉分布变异系数V_、水力半径r_H孔喉长度,和孔喉截面纵横比ε等5个结构参数的影响;结合BLM模型分析,推导出地层因素、渗透率与有效应力间存在乘幂、线性和对数线性等3种响应关系。选取不同地区、不同物性砂岩的地层因素和渗透率的有效应力响应实验数据进行了验证。结果表明,对于高孔高渗砂岩,有效应力作用下地层因素和渗透率变化主要是由于水力半径r_H变化引起的,表现为有效应力作用下的孔喉形变;对于低孔低渗砂岩样品,有效应力作用下地层因素和渗透率发生变化主要是由于配位数z和水力半径r_H变化所导致,即孔喉形状和连通性均发生变化。

This study focused on the influence of the effective stress change on the permeability and the formation factor of sandstone reservoirs.By analyzing the deformation rules of differently shaped pore throats under effective stress,we inferred the influence of the change in effective stress on five structural parameters:coordination number(z),pore throat distribution variation coefficient(Vr),hydraulic radius(rH),pore throat length(l),and pore throat cross-section aspect ratio(").In combination with BLM model analysis,we inferred that three types of corresponding relationships exist between the formation factor,permeability,and effective stress:exponential,linear,and log-linear.Moreover,we selected experimental data on the effective stress response of sandstone from different areas,which were verified using different physical properties and varying formation factors and permeability.The results show that the change in the formation factors and permeability of highly porous and highly permeable sandstone under effective stress is mostly caused by changes in the hydraulic radius(rH)and is manifested through pore throat deformation.The change in the formation factor and permeability of low-porosity low-permeability sandstone samples under effective stress is mostly caused by the coordination number(z)and hydraulic radius(rH)and is manifested through changes in both pore throat shape and connectivity.