Introductions and applications of a self-locking wire-line coring system with a water-shielding bit and a circlip-shielded core barrel

The great progresses have been made in the research of wire-line coring system used in complex formations at home and abroad in recent years. However, the key technology problems that affect coring quality and drilling efficiency have not been well solved, such as the resistence caused by core clamping components when the core gets into the core-barrel and the mud pad at the bottom of jet bits. The common S95 wire-line coring system is selected as the example in our study. Adding stainless steel liner with 0.7 millimetres thickness in the inner core barrel separates circlip components. The methods of increasing the number of water holes at the bottom of jet bit and widening the drainage channels have been adopted in these tests. There are two kinds of core lifters alternatives, one is hairpin spring and the other is clip spring. A new type of wire-line coring system with three-ply core barrels has been developed for drilling in complex formation, which has the advantages of water shielding, circlip-shield and automatic core locking. This new kind of wire-line coring system with hairpin core lifter is tested in the broken formations with strong water sensitivity. The average roundtrip footage is 1.13 m and the core recovery is 94.48%, which is increased by more than 50 percent comparing with the core recovery rate of similar formation nearby. The test has been carried out in the muddy formation with developmental fractures by using the circlip core lifter. The core cutting is as reliable as the circlip used in the ordinary wire-line coring system. The tests show that the coring technology by using liner to separate the core clamping components is feasible, which solves the obstruction of the core clamping components to the soft and loose core, and which is effective to protect the core in original state. The water-shielding jet bit improves the flush effect at the bottom of the bit and reduces the damage of the mud pad on the drilling speed by calculating the reasonable drilling pump volume and the effective number of water holes. This new kind of wire-line coring system is easy to operate and is cheap to use. It is expected to be popular and applied in the current wire-line coring drilling crew in China, which is going to have a strong universality and wide application.