Microfoam Drilling Fluid for Coalbed Methane Extraction Based on Oil Drilling Fluid Technology: Concentration Optimization and Drilling Slag Carrying Simulation

Summary Coalbed methane extraction drilling is prone to stuck drill, blowout, and collapse, making it difficult to achieve efficient gas control. To this end, we developed a high-performance microfoam drilling fluid. Through optimization experiments, we preselected 10 foaming agents, four foam stabilizers, and modified bentonite materials and determined their optimal concentration ranges. In addition, we carried out coal-carrying performance tests and numerical simulations of coal-carrying laws. The results show that the optimal concentration of foaming agent is approximately 0.2–0.6%, the optimal concentration of foam stabilizer is approximately 0.4–0.8%, and the optimal concentration of modified bentonite material is approximately 2–4%. This proves that the microfoam drilling fluid has good coal slag carrying capacity, and that the drilling efficiency can be improved during the drilling process by appropriately increasing the inlet speed of the microfoam drilling fluid, increasing the rotational speed of the drillpipe, and avoiding the eccentricity of the drillpipe. The research results of this paper will provide a theoretical basis and technical support for the research, development, and application of microfoam drilling fluid for gas extraction drilling, which is of great significance for improving the efficiency and safety of gas extraction drilling.