Test of near-horizontal drilling hydraulic reverse circulation coring in leakage formation

Based on the urgent need of accurate exploration of geological anomalous bodies such as collapse columns and small faults in underground coal mines for near-horizontal boreholes coring drilling of leakage formation, the double-wall hydraulic reverse circulation continuous coring technology was proposed, its technical principle and characteristics were analyzed, the matching ø89/42 mm double-wall coring drilling pipes and reverse circulation coring bits were developed. Three near-horizontal coring boreholes were drilled, the functional tests were carried out in a surface mine, the maximum core recovery rate of a single borehole was 83.6%, the maximum roundtrip footage was 69 m and the average drilling efficiency can be up to 3.61-6.26 m/h. The relevant improvement and optimization schemes of double-wall coring tool were put forward to solve the problem of serious flushing fluid leakage in leakage formation, and subsequent tests have shown that the return water flow and flow rate of the core return channel were greatly improved with adopting optimized coring tools. Finally, the problems of borehole annulus slagging and core blocked in the reverse circulation core construction was pointed out and the corresponding solutions were put forward, including using the method of positive and reverse circulation deslagging to solve the problem of hole annulus deslagging and using the method of hydraulic releasing stuck in the center channel to solve the problem of core stuck. The test shows that the double-wall coring drilling tool can meet the operation requirements of underground geological anomalous bodies exploration and provides a new technical approach for underground geological anomalous bodies exploration.