Feasibility of large-diameter wireline coring technology for ultra-deep scientific drilling： Experimental verification from the CCSD-SK-2 East Borehole

Abstract:

To improve coring efficiency in ultra-deep scientific drilling and address the large-diameter coring requirements of the CCSD-SK-2 East Borehole， systematic research on equipment configuration and tool innovation was carried out. The API drill pipe was modified to achieve an inner drift diameter of ≥112 mm， accommodating both conventional trip coring and wireline coring operations. A 6500 m wireline coring winch featuring a rope-guided spooling mechanism was developed， and various combined coring tools centered on a hollow downhole power tool were innovatively designed. Tests in the ?311.2 mm， ?215.9 mm， and ?152.4 mm boreholes demonstrated the overall feasibility of large-diameter wireline coring technology in deep wells， with the optimized drill pipe and automatic rope spooling mechanism performing well. For boreholes of ?215.9 mm and above， hollow downhole power tools are preferable， whereas conventional "three-in-one" tools suffer from insufficient power. Conventional wireline coring achieved good results in the ?152.4 mm borehole； however， components such as the locking latch and landing device are prone to failure due to cuttings accumulation. This study verifies the technical feasibility of large-diameter wireline coring in deep wells， provides technical reserves for ultra-deep scientific drilling exceeding 10000 m， and proposes targeted optimization suggestions for drilling tools and fluids in ultra-deep well environments.