Surface-set Diamond Bit Design for Deep-Sea Operating Environment of Seafloor Drill and Hole-Bottom Flow Field Analysis

Abstract

Drilling sampling technology is an important means for obtaining underground physical data and evaluating mineral reserves. The coring diamond bit is located in the front of the drilling equipment, which can reflect the drilling efficiency and core recovery of the bit when drilling into the coring. In order to improve the drilling efficiency and core recovery, a design scheme of diamond bit for seafloor drills is proposed, which combines the formation characteristics of the seafloor within 300 meters. Based on the fluid dynamics theory and considering the effect of bit rotation on the flow field at the hole-bottom, the effects of bit water passage structure and drilling parameters on the flow field are analyzed. The results show that the designed bit can avoid the core erosion by 80% of the drilling fluid. The rotary speed should be controlled at 250 - 330 rpm, and the pump displacement should be 50 - 60 L/min. When the drilling fluid is up-return along the hole wall, the velocity first rises and then drops, then stabilizes between 0.8 - 1.3 m/s, which meets the range requirements for the standard cuttings up-return and the stability of the hole wall. Finally, the rationality of the bit design scheme is verified by field drilling experiments. The average core recovery percent reaches 85 %, which is about 25% higher than the conventional bit of water passage system.