Abstract
Borehole wall instability in broken formations has long been a significant problem in drilling engineering. Microbe-induced calcium carbonate precipitation (MICP) technology offers a promising approach for solving this problem. This study combines microorganisms and drilling fluid technology for the first time to explore a new drilling fluid technology designed to address the instability of a broken-formation borehole wall. First, we selected a solid-free drilling fluid suitable for the growth of Bacillus pasteurii and formulated a microorganism-containing solid-free drilling fluid. We then conducted an orthogonal-design experiment to investigate the effectiveness of the drilling fluid in enhancing the borehole wall. Finally, we analyzed the borehole wall-enhancement mechanism of the drilling fluid using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that 0.4% sodium carboxymethyl cellulose (CMC) solid-free drilling fluid is suitable for the formulation of microorganism-containing solid-free drilling fluid and that it can cement gravel soil (simulating broken formations) into a whole. The amount of calcium produced in the sample reached 6.63 g, the unconfmed compressive strength was 0.324 MPa, and the permeability coefficient was reduced to 0.202 cm/s. The forms of calcium carbonate crystals generated in the sample were vaterite and calcite, which filled the pores and played a cementing role, thereby increasing the strength of the sample and reducing its permeability. This study proposes new ideas for solving the problem of borehole wall instability in broken formation using drilling fluid techniques and thus has positive theoretical and practical significance.
NSTL