Nipple Profile Milling Operations

Profiles with a well’s completion can become obstacles to workover or remedial operations.

Profiles with a well’s completion can become obstacles to workover or remedial operations. The ID of these nipple profiles may be too restrictive for tools to pass through for operations that may be required deeper in the wellbore, such as tubing cutting, underreaming, fishing, zonal stimulation, or isolation

If the nipple profile can be sacrificed for enlargement, Weatherford can provide a solution with special milling operations. As in any milling operation, general wellbore details and existing well conditions are important considerations. In addition, when using coiled tubing and a downhole motor, it is imperative to establish the following criteria:

• The type of material from which the nipple profile is made.
• The size and type of downhole motor available for the job.
• Whether the well is capable of sustaining a column of fluids or the use of nitrogen, or a commingled drive fluid will be required for the motor.

Nipple milling applications are approached by progressively milling to increase the diameter of the nipple until the required width is achieved and the bottomhole assembly (BHA) can pass freely through the restriction of the nipple without the risk of sticking the BHA. The length of the mill can vary depending on the amount of material that needs to be removed from the nipple. The steps can be spaced out for special milling engagement sequences, and special pilot features can be added for additional stabilization while milling. The goal of the step mill design, which is key when using the smaller downhole motor designs, is reduction or control of the amount of torque necessary to effectively mill.

Weatherford’s ClearCut™ step mill design accommodates the following cutting media:

• Cut-rite or special insert design placement for operations using higher-torque-output motors.
• A mill with a special diamond matrix design to provide a lower-torque-output milling option.
• Placement of the cutting structure on the top-side taper of the mill to allow for back-milling up through the nipple.

It takes longer to mill higher-tensile-grade steel than medium-grade steel. Chrome and similar alloy steels require special cutting structures and techniques because of the smearing effect commonly encountered with these metals.