Application state and prospects of bionic fuzzy-ball drilling fluids for coalbed methane drilling

The bionic fuzzy-ball drilling fluid was developed by imitating bacteria structure. Bionic Fuzzy-ball drilling fluid for underbalance drilling in well CLY-A shows the density of the fluid can range from 0.8 g/cm3 to 1.0 g/cm3 and it can be circulated without extra equipments. Compressed air drilling in well CLY-B proves that the different bionic fuzzy-ball additives varying drilling phases such as air, mist, foam and fuzzy-ball drilling fluid can be converted smoothly. Bionic fuzzy-ball drilling fluids for controlling and killing circulation loss in well DFS-C indicates it can control the leakage in forms of pressure reduced, pressure lost and pressure supported. The multi-branch drilling process in well FL-D shows both the cases of high viscosity with low shear rate and the low viscosity with high shear rate have good performance in cleaning wellbore and enhancing ROP. In well J-E, different formation pressure coefficients exist in the same open hole. The successful drilling proves it can improve the formation pressure bearing resistance in low-pressure section and help safe drilling in formations with narrow dynamic safe density window. Further study of bionic fuzzy-ball drilling fluid should focus on its microstructure, system type and circulation density, to satisfy more specific needs in drilling process.