Evaluation Method for Stress Sensitivity of Reservoir Rock

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.