Simulation study on the influence of different influencing factors on the amount of drilling cuttings

The drilling cuttings method is an important means to determine and predict the risk of coal and rock dynamic disasters such as rock burst. Accurately obtaining the variation law of drilling cuttings is one of the keys to understanding the stress state of coal. In order to further understand the failure process of coal body in drilling process, this study introduces the calculation formula of drilling cuttings based on elastic theory, designs the discrete element model of coal body drilling simulation, carries out drilling simulation experiments under different influencing factors, and puts forward the simulation method of indirectly reflecting the drilling cuttings by the number of discrete particles. The variation laws of the number of discrete particles under different mechanical properties of coal body, confining pressures and hole diameters are revealed. The results show that: the discrete element model based on PFC^3D can effectively simulate the cutting process of the drill bit, the simulation results are basically consistent with the laws obtained by the test, and the number of discrete particles is approximately positively correlated with the amount of drilling cuttings. According to the failure range, the failure area can be approximately divided into drilling failure area and deformation failure area, the drilling failure area is related to the geometric characteristics of the drill pipe, and the deformation failure area is related to the mechanical properties and confining pressure characteristics of the coal body. The mean value of discrete particles in the model is negatively correlated with the strength coefficient and elastic modulus coefficient. In practical application, the influence of mechanical properties such as softness and hardness of coal samples on the drilling cuttings index method should also be paid attention to. Under the condition of different lateral pressure coefficients, the mean value of discrete particles in coal is approximately linear. When the lateral pressure coefficient increases from 1.1 to 1.4, the high displacement area of the hole wall gradually changes from circle to ellipse, and the mean value of discrete particles increases by 8.7%. There is a certain proportion relationship between the mean value of discrete particles in coal under different hole diameter conditions. When the hole diameter increases sequentially from 20 mm to 24, 28 and 32 mm, the phenomenon of borehole stress concentration increases significantly, the displacement of the hole wall increases significantly, and the amount of discrete particles increases by 17.3%, 23.6%, 16.7%, respectively.