A downhole mud motor is used with a drill unit in directional drilling to drill long and deep installations—as deep as 4,500 feet (1,372 m)—through hard rock. A mud motor is shaped like a long cylinder that somewhat resembles the extension of a drill string with a drill bit on the end. The basic parts of a mud motor are a power section, transmission, and output shaft assembly. Its size is also generally determined by its diameter.
 How it Works
Mud motors are powered by drilling fluid referred to as “drilling mud” within the oil industry. The fluid consists of water mixed with bentonite or polymer additives designed to match various soil conditions. The fluid is pumped down through the drill string to the downhole motor, which converts the flow to rotary speed and torque.
Steering a mud motor through rocky strata is achieved with a slight bend in the motor’s housing in combination with the capability to rotate the downhole motor separate from the drill string. In order to bore straight, the drill stem is rotated as the drill bit, powered by the mud motor, fractures and breaks the rock. To switch directions, the operator simply stops the rotation of the drill string and positions the bend so the bit is aligned in another desired direction. Thrust is then applied, causing the bore path to change in the direction of the bend. Because the bend angles on a mud motor are fairly small, directional changes are made very gradually.
Data is used to track and guide the drill head using either a walk-over conventional electronic system or a wireless guidance system. The mud motor also works in conjunction with a stand-alone cycling system. Recycling systems mix the additives and pump fluid into the drill rig. The drill rig then pumps the fluid down the drillhole to power the motor. The fluid gets returned to the recycling system. Solid waste is removed and any remaining clean fluid is then returned to the drill rig and pumped down the drill hole again.