Abstract:Special drilling techniques are needed for drilling of a 5, 000m deep scientific cored hole.The general criterion for the technical design is to optimize the economics of drilling operationunder the prerequisite of meeting the requirements of geoscientific research and of being technically feasibility.The final diameter of the borehole should not be less than 6 inches (152mm), to meet therequirement of logging which is an indispensible means for obtaining geoscientific information.According to the technical level and current status of the drilling techniques in the world, a hybridized drilling technology (rotary drilling/mining drilling) should be adopted for the drillingunder such special conditions. This technology is characterized by installing a high speed topdrive head onto a petroleum rotary rig, which makes diamond wireline coring possible and hasbeen proved in praxis to be the most cost effective method for coring in deep and hard formation.Based on this concept, a technical plan proposed for the drilling of a 5, 000m deep coredhole in hard formation is drawn up, with the main points as follows:(1) drill rig: petroleum rotary rig combined with a hydraulic or electric top drive system;(2) drill rod: Sa inch (140mm) steel rod for wireline coring;(3) core bit: impregnated diamond core bit and/or "Kantanite" core bit ;(4) coring system: combined coring system with hydraulic hammer, retractable bit anddown - hole motor (PDM) incorporated with the wireline coring system;(5)drilling mud: solid free or low solid drilling mud systems with thermostability as highas 150C and having low flow and friction resistance, high cuttings - carrying capacity and having no negative effects on geochemical analysis.
