Experimental study of the mechanical properties and microscopic mechanism of carbonate rock subjected to high-temperature acid stimulation

Abstract

To clarify the effect of acidification on the stress distribution around wells in deep carbonate reservoirs, it is necessary to study the changes in mechanical properties of carbonate rocks under different acid stimulation conditions. In this paper, a novel acid stimulation experiment is designed to investigate the mechanical properties of the carbonate rock through a self-built acid-rock reaction experimental system and triaxial rock mechanics apparatus. The changes in the core mechanical parameters with the acid stimulation time at different acid stimulation temperatures are obtained. Based on stress relaxation, the rheological properties of the core after acid stimulation are explored. The internal structural damage mechanism of the core after high-temperature acid stimulation is as analysed via by SEM. This research finds that the elastic modulus and compressive strength of the core exponentially decrease with increasing of acid stimulation time. The higher the acid stimulation temperature, the faster the core damage rate changes, and the earlier the damage amount tends to stabilize. The core has an obvious rheological mechanical property after acid stimulation. The stress relaxation amplitude exponentially increases with increasing strain during loading. Interestingly, when the acid stimulation temperature reaches 120 °C, a sudden stress drop occurs during stress relaxation. It is also found that the stress relaxation amplitude increases exponentially with increasing acid stimulation time under the same strain level. Moreover, a higher acid stimulation temperature results in greater stress relaxation under a constant acid stimulation time and strain. In addition, the core skeleton is destroyed through acid stimulation, and many complex damaged structures appear inside the core, which leads to a decrease in the core strength, which is the reason for the enhanced rheological characteristics of the rock after acid stimulation. These results can provide insights into the mechanical response mechanism of wellbore acidification.