What is a Mud Motor?

Mud motors have been utilized under specific circumstances for vertical drilling—such as drilling in oil patches where drills have to push through bedrock—for some time. By making several minor adaptations, these tools have also become effective for horizontal directional drilling (HDD) projects. However, many operators remain somewhat in the dark regarding the value of mud motors when it comes to HDD drilling.

Many HDD drillers are well aware of the basic concept of a mud motor and recognize that it is used primarily for drilling through solid rock. However, this is the extent of their knowledge. With that in mind, this article provides valuable insights into the specifics of a mud motor, including its functioning and how this tool can improve both the efficiency and profitability of drilling projects.

How Do Mud Motors Function?

Conventional drilling methods can run into problems when drilling through solid rock. In particular, traditional duckbill or blade set-ups make drilling through hard materials time-consuming and inefficient. Directional shifts are particularly challenging, requiring the drill head’s rotation to come to a complete stop with the driller relying on the rig’s thrust and fluid pressure, paired with a gentle rocking motion, to align the drill on its new path.

In a typical drilling set-up, the directional drilling fluids (mud) are ejected from the system as waste. However, a mud motor derives most of its power from that very fluid by using the flow pressure to spin the drill bit, displacing the force from the rig’s hydraulic motor.

The unique features of the mud motor enable an operator to bring the spin of the drill stem to a complete halt when changing directions, which stops the motor and allows only a small portion of it—where the bit is connected—to continue to spin. The power section of a mud motor relies upon a rotor and a stator, which, together, harness the pressure and flow of the drilling fluid to create the torque and rpm that spins the drill bit. It allows the mud motor to offer rotary cutting and the ability to steer simultaneously.

How Do You Steer a Mud Motor?

Unlike a conventional setup, where the duckbill or blade is placed at an angle, a mud motor is typically established with a 2-degree bend and set back approximately two to three feet from the drill bit. With a conventional setup, the blade deflects as the operator applies thrust, which causes the drill to change directions. However, with the mud motor, the head can be rotated until the bend reaches the necessary direction. The operator can stop any further rotation of the drill carriage while the bit keeps spinning, enabling more accurate steering that requires significantly less effort.

Other HDD Equipment and Necessary Accessories

It is important to remember that mud motors need a great deal of drill fluid to function correctly. You should be prepared to purchase significantly more fluid and use a recycler or reclaimer to pump out the mud, separate the solids, and return it to the system.

Another thing to be aware of the that when using a mud motor, the operator will need to implement a high-flow transmitter housing into the drill string. The fluid passages on this housing help to decrease restriction to avoid fluid pressure drops due to bottlenecks at the transmitter housing. While this can be costly, this equipment is also helpful during conventional drilling, so it is multi-functional and—quite frankly—a necessity.

Lastly, to increase the footage of your drilling, investing in a specialized bit for rock drilling will be incredibly helpful. The most commonly utilized bit used with mud motors is called a tricone. On a tricone, three small balls surfaced with carbide studs fracture the rock, then break it down into smaller pieces. While it is a more expensive piece of equipment than the standard bit, it is worth it.

Additional Information to Review Before Drilling

Mud motors do not necessarily have to be purchased. Unless you will be drilling into solid rock almost all the time, renting this equipment is likely more beneficial to your operation. Mud motors undergo a great deal of stress, causing the efficient HDD tools to wear down over time. After 150 hours of use, they will require a basic service, with a more extensive service needed at 1,000 drill hours. Rather than invest in the specialized equipment necessary to maintain the motor, most operations rely on outside companies to perform maintenance and repairs.

It is critical to obtain and implement a mud motor correctly for it to be a successful endeavor. By purchasing a cheap rock bit, refusing to use the high flow housing, or cutting other corners, you may compromise the efficiency and profitability of the entire drilling job. Trust me; this is not the time to rush things along. However, you will see that working with a mud motor will help you to improve productivity when drilling through rock, which will make the time and financial expense worthwhile.