Experimental research on deterioration of mechanical properties of carbonate rocks under acidified conditions

Abstract Understanding the relationship among the individual factors (i.e., carbonate rock types, acid rock reaction kinetics, deterioration of rock mechanical properties) can provide practical guidelines that can be used for the design and optimization of acid fracturing operation. A comprehensively experimental study was conducted to investigate the acid rock reaction kinetics of carbonate rocks under acidified conditions, and how the acid rock reaction would influence the carbonate rock mechanical properties. In addition, the deterioration mechanism of the carbonate rock mechanical properties is determined by the qualitative analysis of casting thin section images. Results show that the limestone rock is more susceptible to acid dissolution than limy dolomite rock under the same acidified conditions. The limestone rock has relatively large reaction rate constant and low activation energy, however, it is reverse in limy dolomite rock. As a result, the mechanical properties of rocks with relatively low cementation strength could be highly or lowly weakened. The reduction (in percentage, %) in mechanical properties of the limestone rocks with relatively high cementation strength is greater than that of the limy dolomite rocks with relatively high cementation strength. Casting thin section images show that the cementation and fillings of limestone and limy dolomite rocks are calcite and calcite-dolomite, respectively. The non-uniform (i.e., superficial and local deep) and uniform etched pattern (i.e., superficial and symmetrical) occur on the end surface of limestone and limy dolomite, respectively. Consequently, the mechanical properties of relatively high cemented limestone rocks are more significantly reduced than that of relatively high cemented limy dolomite rocks. This work is of great practical guidelines for the design and optimization of acid fracturing operations, as well as the efficient stimulation of carbonate reservoirs.