Study on high-performance micro foam drilling flushing fluid for coal seam extraction drilling

In order to solve the problem that the traditional clean water and anhydrous flushing fluid are easy to cause borehole deformation and collapse, a microfoam borehole rinsing fluid system was constructed by optimizing the foaming agent, foam stabilizer, bentonite and filtration loss reducing agent, and the similar material model of the soft coal seam was established through indoor simulation experiments, and the simulation experiment of the extraction borehole was carried out to analyze the hole protection effect of the microfoam borehole flushing fluid.The results show that: ① The microfoam drilling and rinsing fluid system has moderate viscosity, good rheological properties, high dynamic plastic ratio, small filtration loss, density of 0.38 g/cm3, and half-life of over 90 h, It has a thick hydration film, strong stability, and a normal distribution of particle size, with an average particle size of 158 μm.② The rock-carrying capacity of microfoam drilling flushing fluid is about 67 times that of clean water.③ The expansion of the coal seam rock sample in the microfoam borehole flushing fluid was 0.2 mm, and the rolling recovery rate was 96.4 %, indicating that the microfoam borehole flushing fluid had good inhibition performance and could maintain the stability of the hole wall of the gas extraction borehole.④ The microfoam borehole flushing fluid has good temperature resistance and good hole protection effect, which can effectively prevent water from seeping into the coal seam and prevent the instability and collapse of the hole wall of the extraction borehole.