Preferred Ratio and Properties of Microfoam Drilling Fluid for Gas Extraction in Soft Coal Seams

During the gas extraction drilling process, especially the soft coal seam drilling process, due to the constraints of geological conditions, technical conditions, and other factors, it is easy to encounter stuck holes, blowout, lost circulation, and hole collapse, which affect the realization of efficient gas management. In the petroleum industry, microfoam drilling fluid has unique advantages as a drilling and flushing medium. Through the response surface method, this study conducts a preliminary experimental study on the types of foaming agents, foam stabilizers, modified bentonite materials, and filtrate reducers and determines the optimal formula as 3.98% modified bentonite + 0.586% compound foaming agent + 0.776% foam stabilizer + 1% sulfonated phenolic resin + 2% carboxymethyl starch sodium. The performance of the microfoam drilling fluid system is tested. Subsequently, a simulated soft coal seam drilling test is carried out to verify the effectiveness of the developed directional microfoam drilling fluid for protecting coal rock holes. This microfoam drilling fluid system technology can improve the drilling quality of the sealing section of coal seam gas extraction drilling and effectively improve the gas extraction rate of coal mines.