Research progress on trajectory control technology for geological core drilling

Objective and SignificanceGeological core drilling serves as a critical technical method in geological exploration, with borehole trajectory being a key factor in assessing drilling quality. The borehole trajectory not only impacts borehole safety during construction but also directly influences the accuracy and reliability of geological exploration outcomes. However, challenges such as small diameters, low pipe strength, and continuous coring requirements of the borehole significantly complicate trajectory control. Analysis, Discussion and ProgressBy analyzing the characteristics of geological core drilling, we systematically classify and summarize methodologies for trajectory control. The following results are obtained: First, the primary objective of primary directional boreholes is to obtain the core of the target layer. Design methods for parameters such as inclination angle, orientation, and displacement alongside their depth-dependent variations were analyzed. The applicable conditions and drawbacks were clarified, providing ideas for the use of primary directional boreholes in drilling construction of depths less than 500 meters. It was pointed out that deep boreholes should be used in conjunction with other measures. Second, in terms of packed hole assemblies for geological drilling, we analyzed the use of conventional hole assemblies and large-diameter hole assemblies, and proposed the mechanical theory of the wire coring string with packed hole assembly. Third, regarding controlled directional drilling technology, we analyzed its application in drilling deviation correction and lateral drilling obstacle avoidance. We pointed out the advantages and disadvantages of different methods, indicating that small-diameter bottomhole power drilling tools have obvious advantages. However, due to the requirements of geological coring technology, they have many limitations in geological core drilling. Conclusion and ProspectsThis study reviews the status of geological core drilling trajectory control technologies, identifies key influencing factors, and evaluates various control techniques to enhance exploration precision.