The Design Of Wire-line Coring Rigin Complex Strata

The geological variability of complex strata, also known as unconsolidated stratawhich are not easy to drill throughin drilling engineering, leads to the failure of gaining asatisfactorily high core recovery by applying conventional coring rigs. Two facts contributeto this failure: severe geological conditions which lead to excessive consumption of drillbits, low drilling speed and long hoisting intervals, the absence of core protection devicewhich leads to core sample fractures washed away and results in low core recovery.Aiming at solving the conflict between the high expectations of core recovery inenvironmental science drilling projects and the low core recovery efficiency, this paperdevelops a new type of wire-line coring rig by integrating new design ideas into theoperating principle of conventional S-75series wine-line coring rig and chamfer guidedevice, which meets the high requirement of core sample recovery in complex strata forenvironmental science.With its mature technology the classical set of wire-line coring rigs S-75is widelyused for core sample recovery, especially in well-conditioned hard rocks. However, itssimple core catching mechanism greatly lowers the core recovery efficiency when S-75isapplied in fractured strata. This paper brings out the method of adding a catching spring tothe original core catching device to protect disturbed core, which will greatly improve itsapplicability in complex strata. Also there is the disadvantage with the conventionalS-75that the entire drill string has to be withdrawn to check or to change the seriously worndrill bit. Based on the undercutting principle of step dual-bit drill, this paper develops thedrill bit system whose inner bit heads over the outer bit to undercut the rocks. The inner bitis connected to the inner tube and can be withdrawn along with it, thereby substantiallyimproving the time efficiency and economic benefits. The inner and outer bits are designedwith chamfered in-out splined coupling structure, which guarantees precise positioning ofthe new inner bit and also effectively helps to prevent the forming of dike.The design of the new-type wire-line coring rig contributes to solving core recoveryissues in complex strata. The dual-bit coring drill simultaneously meets the high corerecovery requirement in environmental science and greatly improves drilling efficiency bychanging the inner bit while the drilling string is kept in the borehole. While coming withnormal strata, the drilling rig can be replaced with the conventional coring rig, thereby saving costs with the guarantee of working efficiency.