Chapter 12

Milling Operations


Milling is the main method to remove objects that are stuck in a wellbore by friction, mud, cement, scale, or sand, or there is no tool that can grapple the object because of outside diameters (ODs) versus inside diameters (IDs) or odd shapes (i.e., bit cones). Successful milling operations require the appropriate milling tools, fluids, and techniques. The mills, or similar cutting tools, must be compatible with the fish materials and wellbore conditions. The circulated fluids should be capable of removing the milled material from the wellbore. Finally, the techniques employed should be appropriate to the anticipated conditions and the likely time allotted to achieve the objectives of the operation. ...

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