Analysis of Loads and Stresses of Drilling Tool in Trenchless Directional Drilling

摘要

To evaluate the capabilities of horizontal directional drilling (HDD), the loads and stresses must be determined first. The loads of directional drilling tools, such as weight of drill string, torque and thrust at the cutterhead exerted by the drilling rig, reaction force at the rig, axial friction, circular resistance torque from friction as well as fluid pressure are analyzed with the consideration of structural characteristics of drilling tools. Axial stress, bending and shear stresses from torsion, shear stress from buoyancy force, tangential stress and radial stress from shear force are analyzed. Then, the influence of bottom hole assembly, drill-bit pressure, pulling back force, size of the borehole and density of drilling fluid on stresses of drilling tool with specifying parameters of drill string are analyzed. From the loads and stresses analysis above, the failure reasons of trenchless directional drilling are extrapolated and suggestions for preventing HDD failures are provided.