Research On The CBM Wellbore Stability And Anti-sloughing Fluid

The coal-bed methane(CBM) is one of the critical safety factors for the coal field mining. But meanwhile, it is also one kind of the Green Clean Energies. The coal seam is easily to be collapsed due to the hardness of the coal seam itself is low, cleat development, low mechanical strength. These characteristics raised the difficulty level of CBM drilling while makes more downhole engineering accidents. This problem has seriously affected the development of China’s major CBM drilling technology.This thesis comprehensively analyzed the distribution of well’s circumferential stress for vertical and deviated well model. Explored the mechanism of CBM borehole collapse mechanics. Clarified the effect on wellbore stability by coal bedding plane. The borehole has lower collapse pressure and higher stability when the wellbore trajectory is approximately perpendicular to the coal bedding plane, while the borehole will have higher collapse pressure and lower stability if the trajectory and bedding plans into large angle.Theoretically studied the impact of wellbore circumferential stress distribution and calculation by borehole Mechanics-Chemical coupling effect.Based on the experimental data and analyzing the physic-chemical reaction between drilling fluid and coal bed, this thesis deigned polysulfonate anti-sloughing drilling fluid formulations for CBM drilling and evaluated the application in Turpan-Hami Basin coal field drilling. We gradually derived a series of polysulphonate anti-sloughing drilling fluid formulations in line with the characteristics of different coal field by revising and optimizing the basic formulation in drilling practice. These formulations positively provided downhole safety for CBM drilling.