Traditionally, the standard procedure employed by ADNOC Onshore for re-entry wells sidetracked from a cased hole involved milling a window in the casing and followed by a dedicated elongation run with a mud motor bottom hole assembly (BHA) for kick-off and to achieve desired separation from the original casing/wellbore before pulling out of hole with the motor drilling assembly. This is then followed up with a rotary steerable plus measurement/logging while drilling (M/LWD) assembly to continue drilling the 8-1/2″ deviated section to target landing point (LP). The main reasons for having the dedicated motor elongation run are to get enough separation from the main wellbore (not tracking the original hole) within the shortest distance to avoid the magnetic interference to the M/LWD tools from the casing and to assure not following the previously drilled well. However, associated with this practice are some negative impacts operationally which can be summarized as below

  • High localized dogleg severity (DLS) during the sliding interval with the motor

  • Requirement to make-up and round-trip two separate BHAs before drilling to planned LP

  • Potential hanging of the motor assembly at the window during sliding interval

  • Additional cost due to utilizing 2 different types of drilling bit (Initially TCI for the motor run and then PDC to drill the section)

The only way to avoid those cons is by doing one trip with RSS to exit the window and drill away from the whipstock. The main challenge doing this will be to have enough rat hole to accommodate the BHA (including smart tools with electronics parts) and avoid damaging the BHA components during rotating it inside the casing. This can and has been achieved with a high build rate RSS by some operators but however, use of this technology still exposes the delicate components of the M/LWD tools to possible damage due to contact with the window while rotating the string with the tools still within the parent casing.

The introduction of the motorized rotary steerable system (MRSS) in the suite of steerable drilling assemblies has opened additional window of opportunities. Ability to combine some of the benefits of using a mud motor with that of a rotary steerable system all in one bottom hole assembly without doubt offers the potential of pushing further the limit of performance and productivity. With the MRSS BHA, with a minimum required rathole drilled with the whipstock milling assembly, the rotating part of the BHA will be out of the window prior to start circulation. This paper presents the success achieved with a MRSS system with Near bit Gamma-ray sensor requiring only 18ft rat hole delivered in ADNOC Onshore re-entry wells sidetracked from whipstock window.

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