The paper explores the 7" liner milling operations in re - entry well bores, operations that have become fairly common especially at the interface of corrosive effluents or after an extended life time. This however being a time and efficiency driven choice highlights the need for optimization from both the performance as well as the operational time perspective. The flat time endemic to the milling operation execution however, can be reduced and the operations can be optimized with effective mills, fine tuned rheological parameters of the milling fluid, the BHA stabilization and the finger printing of the milling parameters put in place to execute the entire operation. This paper looks into the various facets of optimization that can expand the avenue of flat time reduction and milling operations execution.

Considering the various wells in the database considererd vis – a – vis the milling operations, a baseline ROP of 2 – 6 FPH for liner milling can be established. The baseline reference for this operation averages out an approximate of a couple of weeks from the well duration and has inherent complications both of which can be circumvented with optimization. Albeit the best proponent for mill selection is the existing liner configuration downhole, however this is one luxury that is not available in most cases. More often than not, the maiden mill run is done in a well with the least amount of data available regarding the existing well casing state. Therefore, adequate mill selection and mill cutting structure preparation hold significane for the successful execution, after all each milling run dictates the progress of the successive one. The paper also looks into the proponents of operational optimization and the denominators that drive the successful execution of the job.

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