Research on the Mechanism of Sand Bridge Stuck Drill in Deep Coal and Rock Gas Horizontal Wells

ABSTRACT Deep coal and rock gas, as an important component of unconventional natural gas, has attracted much attention due to its abundant reserves. However, in the current process of coal and rock gas development, underground accidents of burying drilling tools due to sand bridge stuck drill accidents often occur, which is one of the important difficulties faced by coal and rock gas wells at present. This paper systematically studies the mechanism of stuck drill caused by sand Bridges in deep coal‐rock‐gas horizontal Wells for the problem of stuck drill in sand Bridges. Studies show that collapse and block shedding caused by wellbore instability a key factors in the formation of sand bridges. Traditional models have limited applicability in deep coal‐rock gas reservoirs because they ignore this factor. Based on the drilling conditions, considering the “bulldozer effect” and the influence of coal seam collapse and block drop, the calculation models of the stuck pipe resistance of permeable and impermeable sand bridges were established, respectively. The calculation methods of the sand bridge volume and the additional axial force and torque were derived. Through sensitivity analysis, the results show that the length of the sand bridge, the annular clearance, and the internal and external pressure difference significantly affect the stuck pipe resistance. Among them, the resistance effect of the impermeable sand bridge is particularly prominent. The engineering applicability of the model was verified through the example of the horizontal well for coal and rock gas in Changqing. The research proposes control measures such as optimizing the performance of drilling fluid, staged drilling, and controlling the drilling speed, providing theoretical support and technical reference for the drilling operation of deep coal, rock, and gas horizontal Wells.