Scale and Cement Milling Operations
Scales commonly form as a result of chemical reactions within the wellbore and historically require intervention to restore optimal production levels. Chemical compounds forming hard, adherent scale can accumulate on the tubular wall and cause costly production interruptions. The following are some of the more frequently encountered scales:
- Calcium carbonate
- Calcium sulfate
- Barium sulfate
- Strontium sulfate
- Iron sulﬁde
- Various silicates
- Phosphates and oxides
Excess cement left in the wellbore as a result of cementing operations is also a commonly encountered obstruction, and milling has historically proved to be the most effective method for its removal.
When removing various scale or cement obstructions from a wellbore, the key measure of success is rate of penetration (ROP). The principal factors affecting ROP are the amount of mechanical energy transferred downhole and the design of the mill used to break up the obstruction.
Weatherford’s line of downhole motors is designed to maximize horsepower and safely transfer it to the mill. Both the CTD® line, for heavy-duty milling operations, and the MacDrill™ motor, for either high-temperature or underbalanced applications, have a proven record of performance and reliability in scale and cement milling.
Weatherford’s advancements in mill technology let you tailor the mill selection for optimized milling performance. ClearCut™ mills are designed to pulverize scales and cement; their exceptional durability maximizes the life of their cutting structures and minimizes costly trips to change out mills. Weatherford’s polycrystalline diamond compact (PDC) mills have consistently proved themselves as having superior penetration rates through high compressive-strength barium scales.