Identification of rotational torque and power in HDD

The efficiency and economics of directional drilling is influenced by drilling techniques and technology as well as drilling devices, drill bits – so much different from the ones used for deep drilling. Identification of the torque and power needed for rotating the string and drilling of rocks are of special significance. The present works on drilling techniques and technology (Brouthers & Silverman, 1982; Dvorak, 2006; Finnsson, 2005; Frantzen, 2003; Geborys, 1999; Iseley & Tanwani, 1992; Lubinski & Miska, 1988) do not provide a complex solution to the problems related to identification of torque and power in the drilling process, encountered during shallow HDD drilling at less than 30 m of depth in various types of rocks. Drilling companies frequently do not make use of appropriate procedures and standards systemizing the HDD processes. The results of field surveys made during performing a directional borehole in Rajsk, near the Sola river are presented in the paper. A zone of macroscopically homogeneous rocks was distinguished in the profile. Two very important parameters (especially at large diameter boreholes) were registered at constant values axial stress and rotational speed: torque and power needed for drilling rocks and rotating the string. Additionally, the deflection angle and azimuth of well along the string were measured. A pilot hole was drilled with a single-nozzle bit 0.0762 m in diameter and enlarged with a reamer 0.4 m in diameter. The above parameters were statistically analyzed and their influence on rotational torque and power needed for drilling and rotation of the string investigated. The most favorable regression equations are given in the paper. They account for the influence of the axial stress, rotational speed, length of the string and accumulated intensity of axis deflection on the torque (6 and 7)