Design of Diamond Bits Water Passage System and Simulation of Bottom Hole Fluid Are Applied to Seafloor Drill

The performance of the diamond bit directly affects the drilling efficiency of the seafloor drill. The drill bits used in land drilling are prone to abnormal wear, low coring efficiency, and large sample disturbance in marine exploration. At first, in this paper, the operation and formation characteristics of a seafloor drill are utilized to design a water passage system for bottom-jetting diamond bits based on the multi-objective optimization theory. Additionally, then, fluid dynamics theory and the effects of bit rotation on the flow field at the hole bottom were used to analyze the impact of structural and drilling parameters of the HQ-size bit on the flow field of the waterway system. The linear regression equation of the influence of drilling parameters on the bottom hole velocity field and pressure field is obtained. Finally, a field drilling test of the drill bit was carried out. Considering the effect of the grinding length ratio of the bit on the lopsided wear of the inner and outer diameters, the water passage system parameter design and maximum projection area of the cutting tooth are effective optimization goals to improve the normal service life of the bit. The flow field of the drilling fluid at the hole bottom becomes more turbulent and the efficiency of the carrying cuttings return decreases as the waterway height of the bit increases. The optimal bit rotation speed is 250–400 rpm. When drilling into conventional formations, the pump displacement should be controlled within the range of 50–80 L/min. When drilling into sediment formations, the pump displacement should be controlled within the range of 50–65 L/min. An on-site drilling test verified the rationality of the bit water passage system. This work may enrich the existing theories and designs of the water passage system.

Development of Impregnated Diamond Bit with Primary and Secondary Abrasives Based on Matrix Weakening Theory

Along with economic advancement, diamond bit is widely used in mine exploration and engineering geological investigation. To reduce the cost of impregnated diamond bit and improve its drilling efficiency in highly abrasive formation, this paper designs a diamond bit based on matrix weakening theory, and prepares the matrix from high-grade diamond abrasives and SiC particles. Through theoretical calculation, diamond bits were designed with six different formulas of diamond concentrations and weakened SiC particle concentrations. The theoretical analysis shows that the weakened SiC particle concentration fell within 0-50%; the number of diamond particles dropped from 750,115 to 375,150, saving the diamond cost by 50%. To further explore the life, drilling efficiency, and working mechanism of diamond bit, the apparent form of bit materials was analyzed through field tests, using EPMA-1720 electron probe microanalyzer and GENSIS60 energy spectrometer. The field tests show that: the proposed bit, with 35% of matrix skeleton and 65% of bonding metal, improved the drilling efficiency of ordinary impregnated diamond bit by 68%, while reducing the service life by merely 30%. The apparent form analysis shows that: In the diamond bit designed by matrix weakening theory, the weakened SiC particles could easily fall off the matrix surface, leaving recoverable pits on the surface. The non-smooth form weakens the abrasion resistance of the matrix, reduces the contact area between the crown of the drill bit and the rock surface at the hole bottom, and increases the pressure of the crown on the rock per unit area. The fallen wakened particles participate in the abrasion of the matrix at the hole bottom, improve the grinding ability of the rock powder at hole bottom, and promote the protrusion of new diamond particles in the matrix.

Design and Application of Diamond Bit Water Passage System, Seafloor Drill Parameters

The operation and formation characteristics of a seafloor drill are utilized to design a water passage system for bottom-jetting diamond bits based on the multi-objective optimization theory. Fluid dynamics theory and the effects of bit rotation on the flow field at the hole bottom are used to analyze the impact of structural and drilling parameters of the HQ-size bit on the flow field of the waterway system. Considering the effect of the grinding length ratio of the bit on the lopsided wear of the inner and outer diameters, the water passage system parameter design and maximum projection area of the cutting tooth are effective optimization goals to improve the normal service life of the bit. The flow field of the drilling fluid at the hole bottom becomes more turbulent and the efficiency of carrying cuttings return decreases as the waterway height of the bit increases. The optimal bit rotation speed is 250–400 rpm. When drilling into conventional formations, the pump displacement should be controlled within the range of 50–80 L/min. When drilling into sediment formations, the pump displacement should be controlled within the range of 50–65 L/min. An on-site drilling test verified the rationality of the bit water passage system design and corresponding drilling parameters.

Air reverse circulation at the hole bottom in ice-core drilling

ABSTRACTIce-core drilling to depths of 200–300 m is an important part of research studies concerned with paleoclimate reconstruction and anthropogenic climate change. However, conventional drilling methods face difficulties due to firn permeability. We have developed an electromechanical ice-core drill with air reverse circulation at the hole bottom. We believe that the new drilling system will recover ice cores faster than shallow auger drills, with high efficiency and low energy consumption. The theoretically estimated up-hole speed of the airflow should be not <7.7 m s−1 to allow proper removal of ice cuttings from the borehole bottom. The computer simulation and test results showed that the design of the new ice-coring drill is feasible. The maximum allowed penetration rate depends by square law on airflow.