Abstract:In the process of strategic mineral resources exploration and sampling, the traditional vertical hole faces some difficulties, such as high investment in a single hole and limited access to geological information, which cannot meet the needs of high efficient exploration. Therefore, the directional continuous coring technique is proposed based on wireline coring and directional drilling technology, which can efficiently and accurately obtain geological cores in underground three-dimensional space. To solve the technical difficulties of low drilling efficiency in hard rock, complex force on drilling tools and difficulty in continuous core acquisition, the effects of weight on bit and rotation speed on drilling efficiency, drilling speed and build-up rate on directional coring were studied by simulation. The simulation analysis results show that the weight on bit and rotation speed are proportional to the drilling speed, build-up rate and bend-joint stress. When the weight on bit is more than 30 kN and the rotation speed is more than 230 r/min, the build-up rate of 6°/30 m can be satisfied. The formation stress under the action of weight on bit is more concentrated and the extension depth is small, while the formation stress distribution under the action of rotation speed is wide, reflecting different rock breaking effects. Based on the comprehensive consideration of drilling tool life, the preferred weight on bit is 25~30 kN and the preferred rotation speed is 230-300 r/min. The contact stress between the core and core tube becomes larger with the increase of build-up rate, but the final contact stress will be kept within the stable range. The maximum contact stress was 514.7 MPa at build-up rate of 9°/30 m. This contact stress was less than the yield strength of coring tube. The above simulation provides theoretical support for the coordinated optimization about drilling parameters and deviation capacity of directional continuous core drilling tools.
