Construction and Hydration Mechanisms of MgO-Based Curing Plugging Materials

Numerous magnesium-based curing materials with excellent pumping performance have been developed to address lost circulation during drilling and completion. However, the hydration mechanisms of these materials remain inadequately understood. This study introduced a MgO-based curing plugging material composed of curing agents, structural additives, activators (M), and retarders (HN). The materials were analyzed using SEM, XRD, EDS, and mechanical strength testing. The results indicate that the cured product transitions from Mg(OH)2 to a mixture of Mg(OH)2 and 5Mg(OH)2·MgSO4·7H2O with the addition of structural additives and activators, significantly enhancing the strength of the materials. The retarder extended the initial setting time from 100 to 160 min, improving its practicality for lost circulation control in field applications. Furthermore, while adjusting the curing temperature and curing time had a minimal effect on the final product composition, these parameters promoted further crystal growth. The cured product primarily consisted of approximately 20% free water, 11% oxide, 13% hydroxide, and 52% original components. Based on the Krstulovic–Dabic theory, the hydration process could be divided into three stages: crystallization, nucleation, and crystal growth (NG), phase boundary reaction (I), and diffusion (D). These findings offered valuable insights into the hydration mechanisms of MgO-based curing plugging materials and their potential application in controlling lost circulation during drilling operations.