Application research on the split-tube in drilling of Rossing Z20 Mining Area， Namibia

Abstract:

Aiming at prominent drilling challenges in the Z20 Mining Area of the Rossing Deposit， Namibia， including strong lithologic heterogeneity， interbedded soft and hard rock layers， well-developed primary bedding， brittle disintegration of hard rock masses and densely distributed joints and fractures， this study intends to improve core recovery quality and enhance the reliability of geological logging data. Two boreholes in the mining area， borehole R181 in fractured strata and borehole R239 in intact strata， are selected as research objects. A systematic comparative analysis is carried out between the conventional double-tube coring technology and the split-tube coring technology， based on three key evaluation indicators： core recovery rate （RCR）， rock quality designation （RQD） and core fragmentation index （CFI）， combining with field engineering application effects. The test results demonstrate that the split-tube coring technology achieves remarkably superior performance in all three core indicators compared with the conventional double-tube technology， especially in the fractured strata. This technology can effectively mitigate secondary core breakage and core loss， prevent distortion in rock mass integrity evaluation， and completely preserve the primary structural characteristics of strata. Large-scale field application verification proves that the split-tube drilling technology delivers excellent comprehensive construction performance. A total drilling footage of 10527.37 m was completed， with an average core recovery rate of 95.73% across the whole mining area， and all finished boreholes were rated excellent in construction quality. The technical conclusions obtained in this research can provide reliable technical references for coring construction in the Rossing Z20 Mining Area and similar fractured complex strata at home and abroad， and the split-tube coring technology has broad prospects for popularization and application.