Induced CaCO₃ mineral formation based on enzymatical calcification for bioremediation under different pressure conditions

Enzymatically induced carbonate precipitation (EICP) is widely studied as a promising technique for soil stabilization and consolidation. Most of the studies of biomineralization are carried out at a normal pressure. However, several practical application fields are in high-pressure environmental conditions, which affect treatment effects. In this study, a new high-pressure research apparatus has been constructed and used to provide a maximum confining pressure of 20 bar for sand solidification. In addition, the N-(n-butyl) thiophosphoric triamide (NBPT) addition was proposed to improve the solidification homogeneity at higher pressures. The formed sand columns demonstrated the feasibility of the constructed apparatus for high-pressure sand solidification. The permeabilities of EICP or EICP-NBPT treated specimens both decreased during the treatment regardless of different confining pressures. The increase of confining pressure decreased pore sizes, eventually leading to smaller CaCO3 contents in specimens. With the confining pressure increasing from 0 to 12 bar, the increasing rate of strength for the sample with EICP treatment was 75%, while decreased to 35% and 12% at 16 bar and 20 bar, respectively. The NBPT addition resulted in smaller differences of sonic time values and CaCO3 contents at different parts, achieving higher strengths. The sample with EICP-NBPT treatment had the largest strength at 16 bar. In this study, the difference of strength was attributed to the combined effects of solidification homogeneity and confining pressure. The results demonstrated that the EICP or EICP-NBPT treatments in this study had several promising applications potentials: improving wellbore integrity, reducing near-wellbore pressure loss, and enhancing CO2 sequestration, which benefit the petroleum industry.