A bottom-hole powered hard-rock coring tool independently developed by the Institute of Exploration Techniques, Chinese Academy of Geological Sciences, recently completed sea trials in the Shanwei sea area. For the first time, the hollow bottom-hole powered drilling tool achieved 10.1 meters of drilling in submarine granite formations, recovering 8.69 meters of core with a core recovery rate of 86.04%, far exceeding the IODP hard-rock coring level. The success of these sea trials marks a breakthrough progress by China in the key equipment research for hard-rock coring in ocean drilling.

Sea trial site

Compared with conventional rotary coring, the greatest advantage of bottom-hole powered coring is that the rotational power of the rock-breaking bit is driven by mud, and the drill pipe does not need to rotate. This coring tool significantly improves borehole stability and drill pipe stress conditions, greatly enhancing borehole wall safety and tool safety. Therefore, bottom-hole powered hard-rock coring technology has always been an ideal coring tool for ocean scientific drilling. Over three years, the ocean drilling technology research team of the Institute of Exploration Techniques carried out four rounds of continuous optimization and improvement of the bottom-hole powered coring tool, from principle research to onshore field reliability tests, and developed a φ197 mm hollow screw motor coring tool with a single-run core length of 7.3 meters and a core diameter of φ55 mm. In tests in intact granite formations on land, the maximum drilling efficiency reached 15 meters per hour, with a core recovery rate of nearly 100%. This sea trial was carried out aboard the ocean geological survey vessel Haiyang Dizhi 10, using a construction process combining full-face drilling and coring drilling, and successfully drilled to 80 meters below the seafloor, penetrating the granite formation. During the sea trial, the bottom-hole powered drilling tool fully demonstrated its characteristics of high drilling efficiency, strong stability and good core quality, and all technical parameters met the expected design targets.

This sea trial of the bottom-hole powered hard-rock coring tool is the world's first successful case of hollow screw hard-rock coring, solving at one stroke the original technical challenge worldwide of "hollow screw + wireline coring," and providing a brand-new set of process equipment for ocean scientific drilling and ultra-deep borehole hard-rock coring. It provides strong technical support for China's ocean drilling to penetrate the Moho discontinuity and explore the mysteries of the Earth's deep interior.