Abstract
When employing the wire-line core drilling technology in loose strata, the core recovery rate is often low due to fragmented rock masses and the erosive effect of flushing fluids, severely affecting core quality and drilling efficiency. To address this, the paper designs a hydraulic closed-core cutting mechanism and water-sealed protective core bit compatible with traditional S75 wire-line core drilling tools. Comprehensive analysis and optimization of the design mechanism’s force, flow field patterns, and operational mechanisms have been conducted through numerical simulations, laboratory tests, and field applications. Studies indicate (1) the hydraulic cutting mechanism can smoothly close under flushing fluid action, with stress and strain within safe limits and the sealing area of the core barrel exceeding 75%; (2) post-optimization, the vortex flow within the flushing fluid flow control valve is significantly reduced, with the flow rate at the core after passing through the water-sealed protective core bit being less than 0.6 m/s, effectively protecting the core from being eroded by flushing fluids; (3) the hydraulic cutting mechanism has proven feasible through laboratory testing, with a recommended standard core claw with a 95% protective rate. In actual loose strata, the average core recovery rate reached 97.83%, an 88.13% increase compared to traditional drilling tools, demonstrating high engineering promotion value.
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