Experimental study on transport law of multiphase slag discharge and optimization of well washing parameters in gas lift reverse circulation of drilling shaft sinking

Based on the engineering background of 04. 2 m advanced drilling of central return air shaft in Kekegai Coal Mine, the problem of low efficiency of air-lifting reverse circulation well washing in the construction of vertical shaft drilling method in Jurassic strata in western China was studied. The law of multi-phase coupling migration of liquid, solid and gas in bottom hole and slag discharge pipe was studied by using similar model test and PIV (Particle Image Velocimetry) testing technology. Based on the model test results, the main influencing factors of well washing were analyzed, and the technological parameters of efficient well washing were put forward. The results show that the self-developed coal mine vertical shaft air-lifting reverse circulation slag discharge test device can realize the visual experimental study on the fluid migration characteristics of the bottom hole and slag discharge pipe of drilling method. The rock slag moves in a dynamic cycle of "accumulation―suspension―adsorption―replenishment―re-accumulation" at the bottom of the well. The fluid in the liquid-solid section in the slag discharge pipe moves up and down spirally, while the liquid-solid section oscillates up and down alternately, and the upward velocity distribution has a strong pulsation phenomenon. The movement of the bottom hole fluid is mainly horizontal flow, the vertical upward return of the fluid only exists near the slag suction, and the upward return velocity is positively correlated with the mud circulation, increasing the cutter head speed or mud circulation can increase the bottom hole circulation and radial velocity. The significant influencing factors of slag discharge effect are cutter head speed, gas injection flow rate, air duct sinking ratio and mud viscosity. Based on the engineering background and test results, the drilling parameters related to bottom hole cleaning and slag discharge are cutter head speed 11. 5 r/min and gas injection flow rate 3 500 m?' /h. The research results can provide useful theoretical reference for solving the technical problem of low efficiency of well washing and slag discharge in deep and large vertical shaft drilling in Jurassic strata. © 2024 China University of Mining and Technology. All rights reserved.