Applying whipstocks and casing mills to kick-off out of existing wellbore has become commonplace. However, this operation is becoming more critical because extended ratholes are often required to accommodate long rotary steerable assemblies out of casing before new formation drilling can commence. This extra trip, depending on window depth, can take up to two days worth of rig time and significantly increase well costs. Ideally, the window milling and thole drilling should be performed in one run to improve operational efficiency and cut drilling costs.

To address this developing niche, a new-style formation mill (NSFM) has been developed by Baker Oil Tools (BOT) and Hughes Christensen (HCC). The NSFM utilizes technology from HCC's industry-leading Genesis PDC line. The tool uses a special PDC compound designed to effectively cut both metal and formation. The NSFM also has specially engineered spiral set cutter alignment that reduces vibration while large water courses keep the PDC cutters cool for increased endurance. The NSFM also has the capability of adapting to any BOT whipstock system or can be run as standalone technology, providing a one call solution resource.

Since its introduction, the mill/bit has been used in various regions. Performance has been closely monitored in applications ranging from 4-1/2" tubing (3.800" OD) TT exits to 13-5/8" 88.2# Q125 casing (12-1/4" OD) in deepwater salt to 7" 32# P-110 casing (5-7/8" OD)in 30,000 psi dolomite with chert nodules.

The versatile tool has saved numerous trips on simple hard rock sidetracks in the Rocky's as well as in deep-water GOM plays where rotary steerable drilling systems were being utilized to save trips and push the reachable envelope. The authors will document this cost cutting performance improvement with several in-depth case studies. The authors will also discuss how the NSFM will play an important role in helping operators reach previously un-economical reserves.


A new casing exit technology is proving to be a valuable ally against time-consuming trips in a variety of re-entry applications. The polycrystalline diamond compact (PDC)-based window/formation mill was developed to mill one-trip casing exits through high alloy or chrome casings and difficult-to-mill/drill formations. The ability to depend on a one trip casing exit in areas where hole conditions, casing type and/or formation strength and abrasiveness have in the past demanded multiple trips to complete can mean the difference in an economical project. With today's ever- increasing rig rates and overall drilling costs, reentries are much more attractive and any time that can be saved from the project also means a lower AFE and shorter time to production.

The natural extension of this milling and drilling ability is to extend the rathole as far as possible. In deepwater Gulf of Mexico, that means an extended rathole to fit long rotary steerable drilling assemblies out the window eliminating the need to an intermediate bit trip with a motor kick off BHA.

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