Study on cement-based materials with controllable gelation time for wellbore protection and leakage sealing in shale gas drilling

Abstract:

To address the severe mud loss and borehole wall instability encountered in deep drilling operations such as shale gas exploration in China， this study proposes a gelation time-controlled strategy for wellbore stabilization and leakage sealing. A corresponding gelation time-controlled cement-based wellbore protection and leakage sealing material was successfully developed by compounding Portland cement with organic acid， sodium fluoride， triethanolamine， and aluminum sulfate， enabling precise regulation of the slurry''s setting behavior. The formulation was optimized through factorial design， and predictive models were established for the pumpable period （PPD） and the interval between pumpable period and initial setting time （IST）. The hydration mechanism was elucidated using thermogravimetric （TG-DTG） analysis and scanning electron microscopy （SEM）. Results demonstrate that the material exhibits excellent gelation time-control characteristics and rapid setting response： the PPD can be precisely adjusted within 10~60 min， with a minimum IST of 12 min； the 7-day compressive strength ranges from 18.8 to 27.5 MPa， meeting engineering strength requirements. TG-DTG and microstructural analyses indicate that all four admixtures initially inhibit cement clinker hydration， later transitioning into a promoting effect， with a distinct inhibition-to-acceleration transition point. Their dynamic synergistic interaction establishes a dual-effect control mechanism characterized by "early inhibition and late promotion"， which confers the gelation time-control property. Notably， organic acid only temporarily retards hydration， leading to substantial formation of C-S-H gel and microstructural densification after 7 days， thereby ensuring long-term strength development. This research resolves the longstanding engineering challenge of balancing slurry loss control and setting efficiency in conventional cement-based sealing operations， providing a novel technical solution for wellbore stabilization and leakage sealing in deep shale gas drilling.