Weight-on-bit can be challenging to calculate at surface as downhole motor performance is generally observed from differential pressure and rate of penetration (ROP). If an accurate weight-on-bit (WOB) is maintained, motor performance and ROP can be maximized while controlling debris size. This will increase the efficiency of the entire millout operation. The weight-on-bit can be monitored and manipulated live via new software (Yeung, J. et al. 2015).

The objective of this research paper is to conduct a comparative study that analyzes the performance of the five bladed carbide mill, tri-cone and PDC bits in terms of debris size vs weight-on-bit. Two main criteria will be used for the analysis. Firstly, a test will be carried out in order to determine how the set down force affects the drilling tool in terms of generating smaller debris size. This knowledge intends to improve wellbore clean outs and reduce the number of wiper trips. Secondly, the test will analyze how set down force of the drilling tool affects the ROP on the bridge plug. One specific type of 4-1/2″ bridge plug with a combination of selected mills and bits will be studied in this paper to control the experiment. However, the overall milling parameters may vary greatly depending on the manufacturers, plug, mill, and bit types.

A series of bridge plugs will be milled out in a controlled environment using the five bladed carbide mill and tri-cone and PDC bits. Each bridge plug will be milled out using a different weight-on-bit. After the bridge plug is milled out, all the plug debris is collected, and sorted based on a debris size distribution graph. The ROP will also be measured during the milling process to determine milling efficiency.

In summary, this paper will compare the performance executed by the five bladed carbide mill, tri-cone, and PDC bits. This paper will identify the optimal weight-on-bit to achieve the desired quantitative debris size with these plugs. More studies need to be conducted for different plug types to see how weight-on-bit affects debris size.

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