This paper considers the ongoing development of an electrically powered bottom hole assembly that has been designed for use in closed-loop, coiled tubing drilling (CTD) applications.

The electric BHA has been conceived and designed through a European Drilling Engineers Association [DEA(E)1] joint industry project. This paper introduces the project and reviews its progress to date.

Electric coiled tubing drilling, or E-CTD, was delineated as a three phase project to stage progress and reduce technical risk. Phase I of the project, completed in late 1997 was designed to prove the feasibility and concept using standard motor technology.

Phase II, currently in a bench testing programme, intends to deliver a fit-for-purpose electric downhole motor (EDM) suitable for drilling a 3.75″ hole. The motor is being incorporated into an electric bottom hole assembly (BHA) which incorporates pressure, temperature and vibration sensors. This is shortly to be field tested in Aberdeen.

Phase III of the project, scheduled to start mid-1999, integrates geo-steering and variable-bend directional technology to provide what has been termed the ‘all electric’ BHA. The ultimate goal of the project is to integrate the electric motor into a closed-loop drilling system. It is envisaged that, based upon feedback from near-bit sensors, such a system would be able to automatically adjust drilling parameters to optimise drilling performance.

Upon successful completion of basic closed loop functions, the intention is to incorporate the controlability of the BHA into what they describe as an ‘intelligent’ drilling system. This paper outlines a definition of this ‘intelligence’ and the authors also provide an insight into how far they believe that this technology may be taken, in terms of the autonomous decision making ability of a surface computer.

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