Experimental research on decreasing coalbed methane formation damage using micro-foam mud stabilized by nanoparticles

For the low porosity and pressure coalbed methane(CBM)reservoirs in China, the paper adopted the technology thought of combining the temporally plugging technology of the nanomaterials with circulative micro foam drilling fluid. Through the methods of evaluation on the stability of foam drilling fluid, performance tests of drilling fluid and microstructure observation, the expansibility, rolling recovery rate and gas permeability test of original coal rock, the ability of micro-foam mud stabilized by nanoparticles on reducing the damage of CBM reservoir was evaluated. We found that firstly, nanoparticles can improve the stability of foam drilling fluids. Furthermore, the micro-foam mud stabilized by nanoparticles have the advantage of high-controllable density (0.7-1.0 g/cm3) and viscosity, which can adapt to the drilling requirements of the low porosity and pressure coal seam, and which can effectively restrain the adsorption and swelling of coal rock matrix. Finally, the micro-foam mud stabilized by nanoparticles can effectively plug the low porosity and permeability coal seam, while the gas permeability recovery rate of coal is as high as 72%-96% after slice processing for the surface of pollution section of coal rock. With the integrative consideration, the micro-foam mud stabilized by nanoparticles can not only protect coal seam stability, but reduce the reservoir damage of coalbed methane, and is suitable for the low porosity and low pressure coalbed methane reservoirs drilling.