The Multi-Inhibitive Drilling Fluids for Coalbed Methane Formations

In order to control the wellbore stability in the CBM drilling process, the drilling fluid with strong plugging, clay hydration inhibition and anti-collapse properties should be comprehensively considered. The multi-inhibitive CBM drilling fluid was prepared by introducing sodium formate, which is an excellent inhibitor, into the fuzzy ball drilling fluid. Laboratory evaluation experiments showed that the prepared multi-inhibitive CBM drilling fluid based on fuzzy ball and sodium formate, displayed favorable multi-inhibitive properties, not only for its excellent inhibition performance on clay hydration, but also for its strong plugging and anti-collapse abilities. The results showed that the specific surface area and grain size of clay particles were almost unchanged, when the concentration of sodium formate was 30%. Besides, the prepared drilling fluid can effectively plug fractures in coal plugs as the injection pressure increased to more than 20MPa after plugging. Moreover, the uniaxial compressive strength of coal plugs increased by 43.3% after the displacement of the prepared drilling fluid. During field applications in more than 40 CBM wells such as Well-X, Well-Y and so on, the results showed that the prepared multi-inhibitive drilling fluid can successfully maintained the wellbore stability during drilling in CBM wells.