Research progress on trajectory control technology for geological core drilling

Geological core drilling is one of the important technical means for geological exploration, and the actual drilling trajectory of the borehole is an important parameter of drilling quality. It not only affects the safety inside the borehole during drilling construction, but also relates to the quality and accuracy of geological exploration. The limited conditions such as small bore diameter, low pipe strength and continuous geological coring which lead to difficult to control the drilling trajectory. Based on the analysis of the characteristics of geological core drilling, the trajectory control methods of geological core drilling were systematically sorted out, classified and summarized. The following research results are obtained. First, The primary goal of primary directional hole is to obtain the core of the target layer, analyzed the design method of parameters such as the inclination angle, orientation, displacement, etc. of the borehole and their variation with depth, and clarified the applicable conditions and drawbacks, provided ideas for the use of primary directional hole in drilling construction less than 500m, and pointed out that deep holes should be used in conjunction with other measures. Second, in terms of packed hole assemble for geological drilling, analyzed the usage of conventional hole assemble and large-diameter hole assemble, and proposed the mechanical theory of wire coring string with packed hole assembly.Third,around controlled directional drilling technology, analyzed the application in drilling deviation correction and lateral drilling obstacle avoidance, 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.Through a review and analysis of the current status of geological core drilling trajectory control technology, clear identification of key factors affecting drilling trajectory and various techniques for controlling drilling trajectory, which can provide useful references and research ideas for improving the exploration accuracy of geological drilling.