Effects of Proportion of Anhydrous CaCl₂ on the Expansion Properties of Soundless Cracking Agents

Abstract

Anhydrous calcium chloride (CaCl2) can improve the problems of long fracture time and low efficiency in fracturing hard rocks with soundless cracking agents (SCAs), but the effect of the proportion of CaCl2 on the expansion properties of SCAs and its optimal ratio are less studied. In this paper, a comparative analysis of SCAs with different contents (0, 0.4, 0.8, 1.2, and 1.6 wt %) of CaCl2 was performed. The macroscopic morphology, expansive pressure, hydration temperature, and potential were monitored using a static strain system and a temperature and voltage acquisition system, respectively, to investigate the effect of CaCl2 on the performance of the SCA. The results showed that CaCl2 could improve the hydration efficiency of the SCA. Compared with group “a” (0%), the volume expansion ratio of SCA in group “e” (1.6%) decreased by 17.9%, the initiation time of expansive pressure development and the time required for reaching the peak pressure were reduced by 96.25 and 96.48%, respectively, the peak expansive pressure was increased by 109.02%, and the time for reaching the peak temperature was reduced by 92%. The catalytic and adsorption effects of CaCl2 promoted the hydration of calcium silicate hydrate (C–S–H), which shortened the “dormant” period of SCA, increased the peak expansive pressure, improved the lag of peak temperature development, and significantly improved the hydration efficiency. The maximum potential gradually decreased, the minimum potential first decreased, increased, and then decreased, and the peak expansive pressure decreased with the increasing of the maximum hydration potential. The mechanism of the effect of CaCl2 on the hydration of SCA was explained according to the development of potential and catalytic principles. Considering safety and economy, the addition of 1.2% CaCl2 is preferred to enhance the hydration performance of SCA. This study is important for SCA applications in industry.