The application of coated superabsorbent polymer in well cement for plugging the microcrack

• SAP has adverse effects on the pumpability, strength and integrity of cement.
• Gypsum–chitosan–gypsum coated SAP is used in well cement to plug the microcrack.
• Percolation theory is taken to calculate the dosage of coated SAP.
• Results show that successful plugging of microcrack is achieved.

The research objectives are designed to realize the application of superabsorbent polymer (SAP) in well cement to plug microcrack. Gypsum–chitosan–gypsum coated SAP is proposed. Percolation theory is used to research plugging microcrack mechanism. According to the exact analytical solution of square plane percolation threshold, dosage threshold of coated SAP microspheres is calculated as 28.40%, which can deliver the plugging of microcrack. The method of manufacturing quantitative microcrack is established, and self-designed instrument is employed to test plugging performance. The results show the ability of plugging microcrack when the dosage of coated SAP microsphere is higher than the threshold.