低渗透储层应力敏感分析

Stress Sensitivity Analysis of Low-permeability Reservoirs

实验研究了低渗透岩石有效围压与渗透率之间的关系,以原始储层有效应力(上覆岩层压力与原始储层孔隙压力之差)为有效围压基准来评价低渗透储层的应力敏感性。实验结果表明:此应力敏感评价方法比较接近储层岩石的真实应力状态,得到的应力敏感伤害能反映真实的地层情况;有效围压与渗透率间满足二次多项式的关系;岩石的弹塑性变形使得压敏伤害是永久且不可逆的。理论计算表明,在实际生产中井底存在渗透率漏斗,压敏效应对气井影响显著。恒速压汞测试喉道结构结果说明储层的喉道分布特征决定了岩石的应力敏感程度。

The correlation between effective confining pressure and permeability for low-permeability rocks has been studied in laboratory.The effective stress of original reservoir(a difference between overburden stress and pore pressure in original reservoir)was selected as a reference effective confining pressure to evaluate the stress sensitivity in low-permeability reservoirs.The experimental results show:(i)this evaluation method can closely reflect the actual stress,and the obtained damage caused by stress sensitivity can also reflect the actual strata;(ii)the quadratic polynomial correlation is found between effective confining pressure and permeability;and(iii)the pressure-sensitive damage induced by elastic-plastic deformation is permanent and irreversible.Through the theoretic calculation,we found that there exists a permeability funnel in downhole,and the pressure-sensitive effect makes a significant impact on gas well.The test result of throat structure by the rate-controlled mercury indicates the stress sensitivity level is determined by the throat distribution of reservoirs.