Mechanical behavior of salt rocks: A geomechanical model

Abstract

The geomechanical behavior of salt rocks is a significant concern during drilling and development operations in some hydrocarbon reservoirs and underground gas storage sites. In this study, the static and dynamic salt rock geomechanical properties from a field in southwest Iran were evaluated using experiments such as waves' velocities, and thermo-mechanical coupled uniaxial and triaxial compression tests. As a result and by considering both the petrophysical well logs and laboratory data of the waves’ velocities, it is observed that the elastic properties of the core samples are concentrated within a narrow range unless an abnormality causes scatter. The results of uniaxial compression tests showed that rock strength decreases with increasing temperature linearly. In addition, the reduction of rock strength was observed with increasing porosity of the core samples as expected. In the case of triaxial compression tests, applying confining pressure on the core sample caused an increment in rock strength, while temperature decreased rock strength. The temperature also increased cohesion and decreases friction angle. The ratio of changes in stress to strain was used to investigate the dynamic changes in the geomechanical state. The maximum 0.25 damage factor was observed for the core samples for different definitions of the damage factor. Finally, we propose a novel analytical model to predict the stress-strain behavior of salt rocks at different conditions. The model was validated using experimental results and indicated a satisfactory accuracy.

Keywords

Salt rock / Underground gas storage / Geomechanics / Dynamic and static mechanical properties / Transition zone / Damage factor

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