Self-sealing performance of oil well cement incorporating pH-sensitive superabsorbent polymers: Experimental and numerical analysis

This study develops a novel pH-sensitive superabsorbent polymer (P-SAP) to enhance the self-sealing performance of oil well cement. Synthesized from dimethyl aminoethyl methacrylate (DM) and acryloyloxyethyltrimethyl ammonium chloride (DAC), P-SAP exhibits selective absorption behaviors under different conditions: it maintains a low water absorption rate in highly alkaline cement slurry to avoid compromising cement properties, but rapidly swells upon exposure to formation water when cracks occur, effectively sealing the fractures and restoring cement integrity. Various techniques were employed to comprehensively evaluate the thermal stability, pH sensitivity, water absorption behavior, and microstructure of the synthesized P-SAP. Experimental results indicate that P-SAP has good thermal stability and strong pH-sensitive swelling behavior , with an absorption ratio in cement slurry approximately one-eighth of that in fresh water. Cement slurries with different P-SAP dosages (1 %, 2 %, and 3 % by weight) were prepared, and fractures were induced using the Brazilian splitting method. Micro-CT scans quantitatively assessed the crack sealing effects, showing that P-SAP significantly improved the sealing efficiency. In cement samples containing 3 % P-SAP, numerous interconnected pores transitioned into isolated voids, with permeability decreasing by nearly 90 % within the first hour. Additionally, a theoretical model based on fractal geometry and elastic mechanics successfully predicted the self-sealing performance under various P-SAP concentrations, particle sizes, water absorption capacities , and crack widths. Sensitivity analysis further revealed that P-SAP particle size and content had the most significant impact on sealing efficiency, providing a quantitative basis for the optimized design and application of self-sealing materials in oil well cementing systems under various downhole conditions . • A novel pH-sensitive superabsorbent polymer (P-SAP) was synthesized. • P-SAP maintains low water absorption in alkaline cement slurry. • Micro-CT showed significant crack healing efficiency with P-SAP. • Permeability in cement samples with 3 % P-SAP decreased by 88 %. • Sensitivity analysis identified particle size and dosage as key factors for self-sealing.