Interactive mechanism of manufacturing factors on the properties of microbial cementing slurry

Abstract

In recent years, there has been an increasing interest in microbial self-healing technology in the field of well cementation due to its environmentally friendly, high efficiency, low maintenance cost, and intelligent characteristics. Previous studies have proved that the mechanical strength, setting time, and permeability are the fundamental properties of self-healing cementing slurry which determine the quality of well cementation and the recovery of oil and gas. However, limited research was reported on the effect of manufacturing factors on those basic properties of microbial self-healing cementing slurry in the field of well cementation. In the process of preparation, the air is introduced into the microbial self-healing cementing slurry, causing macropores in the cement stone. Besides, the ammonia produced by microorganisms also results in pores with various size in the microbial cement stone. Those pores which are not conducive to the development of mechanical strength of cement stone might develop into cracks, leading to the failure of well cementation, even causing severely fluids channeling in the wellbore. Therefore, it is of great significance for us to explore the cause of pores in microbial cement stone and choose the proper manufacturing parameters for the field application. In this paper. we studied the influence of manufacturing factors including stirring rate, defoamer dosage and curing ages on the mechanical strength and durability of microbial cement stone. Besides, we explored the interaction mechanism between micro pore structure parameters and macro properties such as compressive strength and permeability of microbial cement stone by the computed tomography technology. The results showed that the number of pores in the microbial cementing slurry was increased with the stirring rate, whereas it was reduced with the increase of defoamer dosage and the extension of curing ages. We also found that there was a poor correlation between the pore structure parameters such as porosity, radius of pores and throats, pore throat ratio and mechanical strength, but a positive correlation between the pore throat ratio and permeability. Moreover, the optimal manufacturing parameters were suggested for the possible field application in this paper. These findings provide a theoretical guidance for the fabrication and application of microbial self-healing cementing slurry in the underground construction buildings besides the well cementation.