Mud Motor Seals

Mud Motor Description

Mud motors are used for various drilling tasks such as straight hole, horizontal, directional, and short-radius oil field drilling, river crossings, and other utility drilling. An oilfield mud motor includes a bearing assembly, with a shaft that is rotated by a power section, which is typically a positive displacement motor that is driven by drilling fluid circulation. The shaft rotates a drill bit, against the formation while axial and radial bearings guide the shaft and react the drilling forces between the bit and the drill string.

For directional drilling, a small bend angle is provided between the power section and the bearing assembly. This bend angle gives mud motors the ability to drill curved or straight holes selectively. Drill string rotation produces a straight, slightly oversized hole. In the absence of drill string rotation, the hole curves in the direction of the bend.

Schematic of a Typical Oilfield Downhole Drilling Mud Motor

Surface pumps are used to circulate the drilling fluid to flush rock cuttings to the surface for disposal. The drilling fluid flows down through the bore of the drill string, exiting into the annulus of the well through the jets in the drill bit. These jets are not shown in the diagram above. The cuttings are flushed up the annulus of the well by the returning drilling fluid. The annulus pressure is substantially lower than the drill string bore pressure due to the pressure drop that occurs as the drilling fluid passes through the drill bit jets.

In sealed bearing mud motors, drilling motor seals are used to retain the bearing lubricant while excluding the drilling fluid and abrasive cuttings. Kalsi Engineering offers several effective options for mud motor seals, which are discussed in more detail below.

Mud Motor Bearing Assemblies

Mud motors fall into two categories based on their bearing types. These are described in more detail below:

  • Mud Lube Bearing Assemblies: Designed to withstand extreme drilling conditions, mud lube bearing assemblies are a more traditional mud motor type. However, these types of bearing assemblies tend to have a higher repair and maintenance cost than sealed bearing assemblies.
  • Sealed Bearing Assemblies: Alternatively called oil lube bearing assemblies, sealed bearing mud motors are exceptional regarding performance and typically can take higher torques for longer periods of time than mud lube bearing assemblies.

Additionally, these assemblies tend to be axially more compact, facilitating short-radius drilling. They may also employ off-the-shelf conventional bearings and typically have a lower total repair and maintenance cost as compared to mud lube bearing assemblies.  Kalsi Engineering provides a family of rotary shaft seals for sealed bearing mud motor assemblies.

Mud Motor Seal Locations

Sealed bearing mud motors have several rotary seal locations, and all are critical to reliability. These seal locations include:

  • Fixed Location: A rotary seal in a fixed location is used to withstand the high-pressure differential between the lubricant and the well annulus pressure.
  • Axially Floating Pressure Compensation Piston: A rotary seal in an axially floating pressure compensation piston is used to balance the lubricant pressure to the drill string bore pressure.
  • Axially Floating Barrier Piston: A rotary seal in an axially floating barrier piston protects the high-pressure seal from the drilling fluid.

The rotary seals in the two floating pistons are exposed to the severe abrasive content of the recirculated drilling fluid, and all seal locations are subject to shaft motion resulting from drilling forces and power section rotor thrust and nutation. Each location presents its own unique challenges, including high differential pressure at the fixed location seal, and reversing pressure and sliding motion at the piston-mounted seal locations.

State of the Art Oilfield Seals

The lack of reliability and short life of conventional seals had previously limited the acceptance of sealed bearing assemblies, but the Kalsi Seal has allowed them to attain widespread use in mud motor drilling. The reliability, ease of maintenance and economics of the Kalsi Seal have been proven by the thousands of motors that use them today. Kalsi Seals represent state-of-the-art mud motor seal technology. Several oilfield seal customers have achieved runs more than 500 hours long.

Guidelines for implementing Kalsi Seals in mud motors and other oil field mud seal applications are included in the Kalsi Seals Handbook. The sheer volume of information can be overwhelming, so we’ve organized it to make it as accessible as possible for anyone to find the information they need. Read Chapter E3 to find the most direct information on the use of Kalsi Seals in mud motors.

Contact Kalsi Engineering for More Information

Kalsi Engineering, Inc. is a leader in providing engineering products and services for the energy, petrochemical, manufacturing, and mining industries. Kalsi Seals are world-renowned for their longevity and state-of-the-art status, the result of pioneering research in hydrodynamic lubrication. On top of these products, Kalsi Engineering also provides engineering consulting services backed by decades of experience in the engineering field.

Whether your company is interested in purchasing Kalsi Seals or needs an experienced engineering resource for your next project, Kalsi Engineering can help you find the best solutions. Contact Kalsi Engineering today to request a quote, or to learn more about mud motors and our recommendations for Kalsi brand rotary seals for your application.