7/25/2023 0 Comments Drilling hydraulicsMining drilling (through hard formations) consists In small rods rotating at a high speed but inside a hole with nearly the same dimensions (the rod/hole diameters ratio is about 0.90). This conventional technic is largely experienced all around the world and empirical rules are deduced to help drilling designers. Conventional drilling in sedimentary formations use small rods rotating at a low speed inside a large hole (the pipe/hole diameters ratio is about 0.30). Two main different technics are used in drilling. Tests realized in a slimhole well have allowed to validate the theoretical assumptions. The final output is the compromise which integrates all these requirements for a successful operation. Outputs are annulus thickness, drilling parameters (including mud flow), and mud characteristics, all to be respected to reduce slimhole drilling problems. The developed model takes into account mud rheology, drill string rotation and eccentric position of drill string. Therefore, it is essential in slimhole to investigate drilling hydraulics, using basic theoretical equations derived from fluid mechanics. To transfer that drilling method to the oilfield and keeping high rotation speed and small annulus, many problems occur due to the sedimentary type of formations drilled, and hydraulics become crucial for following points of view : the lifting up of cuttings in the annulus (no balling up), the well bore stability, the cleaning of the bit, the differential mud pressure in the annulus, the hydrodynamic lubrication between rods and the well bore. In this context, the drill string rotates at high speed very close to the hole wall, which is in general of good stability. Drilling in small diameters is not new : the mineral industry currently drills slim holes in hard rocks.
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