Bearing Assembly of Downhole Motor is used to transmit motor rotary dynamic force to the bit, meanwhile to withstand axial and radial load from drilling weight.
earing Assembly of Downhole Motor is used to transmit motor rotary dynamic force to the bit, meanwhile to withstand axial and radial load from drilling weight. Inside of the Bearing Assembly, EFU PETRO uses TC Radial Bearing and a stacked thrust bearings. The thrust bearings support the downward force resulting from the “weight on bit” (WOB) and the loads from the combination of hydraulic thrust and weight loads from internal components.EFU PETRO provides different bearing assemblies, designed to meet the diverse requirements of the drilling industry.
1) Bit nozzle pressure loss is 7.0 Mpa, EFU PETRO uses a stacked multiple balls design for the thrust bearings. The thrust bearings support the downward force resulting from the “weight on bit” (WOB) and the loads from the combination of hydraulic thrust and weight loads from internal components.
Rolling Element Bearings (Ball Bearings)
Rolling element bearings, or ball bearings, have conventionally been used to react thrust, or axial, loads in downhole mud motors. When low rpm power sections are used in the application such bearings provide suffcient life and reliability. However, bearing component fatigue causes life to decrease linearly as speed increases; fatigue makes ball bearings unsuitable for high rpm motors. In addition to life, friction and horse-power losses are often of interest in drilling. Ball bearings are referred to as frictionless bearings due to the rolling nature of the elements; however in practice frictional losses exist duo to rolling resistance and sliding. An order of magnitude approximation of the coefficition of friction (CoF) for an angular contact bearing operation in ideal non-abrasive lubricant conditions is 0.0032. In drilling mud, the CoF can be assumed to be significantly higher.
2) Bit nozzle pressure loss is 14.0 Mpa, EFU PETRO uses PDC thrust bearings or Hydronamic bearings . It has longer life and higher bearing loading capacity.
Sliding Bearings (PDC Bearings)
Polycrystalline Diamond Compact (PDC) bearings have historically been utilized in high speed motors as they are not subjected to the same fatigue mechanism experienced by rolling element bearings. These bearings operate in a sliding manner and relative moving parts to transmit load. Common PDC bearings designs use an array of round PDC pads mounted to a ring.
In the case of PDC the value of coefficient of friction (CoF) can be estimated by 0.05 to 0.08.
Hydrodynamic, or fluid-film, bearings function by separating the bearing faces by a layer of visious fluid. A conventional hydrodynamic tilt-pad bearing was modified for use in downhole operation. The modification includes the use of spring mounted silicon carbide pads which:
- allow pads to tilt for fluid entrainment into the bearings surface
- allow deflection in the axial direction for efficiently sharing thrust load among pads and between stacked bearings
- resist mud abrasion due to hardness of the advanced ceramic
The coefficient of friction (CoF) for the hydrodynamic bearing operation in water can be estimated to be 0.0004.
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