储层岩石的应力敏感性评价方法

Evaluation Method for Stress Sensitivity of Reservoir Rock

油气藏岩石同时受外应力(外压)和内应力(内压,孔隙压力)的共同作用。油气藏岩石对外应力的敏感程度,用外应力敏感指数进行评价;对内应力的敏感程度用内应力敏感指数进行评价。油气藏的外应力敏感指数远大于内应力敏感指数。由于油气藏生产过程中外应力不发生变化,内应力随开采过程而不断变化,因此,油气藏岩石的应力敏感程度应采用内应力敏感指数。岩石的外应力敏感指数仅受敏感常数的影响,岩石的内应力指数受敏感常数和孔隙度的共同影响。因加载过程存在塑性变形,应力敏感性评价应采用卸载曲线。

Reservoir rock is affected simultaneously by external stress(external pressure) and internal stress(internal pressure and pore pressure).Sensitivity of reservoir rock to external stress is evaluated with sensitivity index of external stress,while sensitivity to internal stress is evaluated with internal sensitivity index.Sensitivity index of external stress is much higher than that of internal stress.In the process of production,external stress does not change,while internal stress changes.Therefore the sensitivity of reservoir rock should use the sensitivity index of internal stress.Sensitivity index of external stress is only affected by sensitivity constant,while index of internal stress is affected by both sensitivity constant and porosity.Because loading process has plastic deformation,unloading curve should be used for sensitivity evaluation.