Low Invasion Corehead Reduces Mud Invasion While Improving Performances

Abstract

A corehead was designed, manufactured and tested to reduce fluid invasion of the core. This is obtained by minimizing the exposure time of the core to the drilling fluid in increasing the rate of penetration (ROP). The design incorporates a medium heavyset polycrystalline diamond compact (PDC) cutting structure developed in accordance with cutting models and balancing methods used for drill bits. The highest ROP is achieved by a particular hydraulic design: flow ports shape and positioning to clean the cutting structure enhance the drilled cuttings removal while preventing drilling fluid in the throat of the corehead. Moreover, an internal lip works with a special inner barrel shoe to effectively seal off mud flow from the throat. All the design features have been subjected to laboratory tests, including measurement of pressure drop across the corehead and flow visualization studies. Flow visualization tests include high-speed filming of the flow and paint tracing to indicate the special flow pattern. In conjunction with lab tests, a numerical simulation was performed using fluid dynamics software to optimize hydraulic parameters. The low invasion core bit has been used in numerous applications. The performance achieved was significantly better than the average achieved over a period of years using various PDC coreheads. The rate of penetration was increased by a factor of 4.8 and bit life by 2.3 (often with reusable condition).

Rotary ultrasonic machining of rocks: An experimental investigation

“…Cutting force increased as drill bit diameter increased for all three rock types as shown in Figure 11. The increment of cutting force from drill bit diameters (9, 7) mm to drill bit diameters (12,10) mm was much lower than the increment of cutting force from drill bit diameters (12,10) mm to drill bit diameters (15,13) mm, despite the difference between the effective cutting areas of the two drill bits being constant.…”

“…This method increased the drilling depth and decreased the axial force, torque, and tool wear. 8,9 Clydesdale et al 10 developed a core drill bit for the core drilling of rocks, which reduced the fluid invasion and resulted in a higher penetration rate compared to that when using a conventional polycrystalline diamond compact core bit.…”