Deepwater drilling has introduced the oil industry to a whole array of new technical challenges in constructing a well bore to a reservoir deep below the ocean. To build wells with similar dimensions used in shallower water has resulted in a new generation of rig with enormous capacity for riser tension, drilling mud volumes and casing storage. These units are extremely expensive to construct and operate. In addition there are only a limited number available which usually are locked into long term contracts. Many offshore operators have renewed interest in slimmer well construction1–8, in the search for providing them with the capability to drill in deep water without compromising the hole size across the reservoir. Typically this involves sacrificing one or two contingency strings in the process. This paper will present one development which has focused on retaining the necessary number of casing strings (including contingency) to TD while reducing the surface casing sizes to fit within the 14" riser envelope. In addition, with the arrival of new commercial materials and processes, this new well construction process offers exciting potential for low cost deepwater exploration and testing from a DSV. Introduction With the current trend towards deepwater operations smaller riser and casing configurations offer significant advantage over conventional well architecture. Figures 1 and 2 illustrate two potential casing configurations using this technology. The first illustrates the application of a taut leg moored 3rd /4th generation rig employing a 14" riser (the limit of rigs riser tension, mud and casing storage capability in great water depths). The second and slightly more radical application of this technology illustrates an 8" reeled riser from a DSV deploying the coiled casing option. Both these examples illustrate how this innovative solution will broaden the range of options for well architects/engineers. The common approach throughout all of the well construction processes described in this paper is a series of liners, with tiebacks to previous liner tops as required. Finally the well is completed with a production tubing tieback to surface. The main technical advancements are; A unique liner hanger system which mechanically seals the new liner into the shoe of the previous liner, forming a high pressure metal to metal seal in the process, while still retaining the same tensile load capacity as the virgin pipe. A novel conveyance system which allows for a high fluid circulation rate while the liner is being deployed and landed in the well, with a conventional mode for circulating and cementing operations. Technology Development This project has focused on reducing the clearance between subsequent casing strings to construct a flow path with optimum dimensions to/from the reservoir while significantly reducing the casing dimensions at surface. The casing deployment process includes a circulation method which avoids the casing acting like a huge piston exerting excessive pressure on the open hole.

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis 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.

As operating costs escalate and the oil price remaining stubbornly low, now more than at any time in the history of the oil industry the economics of every phase of business must be minutely examined from the exploration and appraisal through to production. In addition to this, another problem arises when dealing with a project such as coiled tubing drilling, as whilst this technology will provide a similar end product to conventional drilling practices it is such a departure from conventional drilling practices as to create scepticism. This paper describes some of the ground work involved as part of a feasibility study carried out for coiled tubing drilling for a situation of drilling from top hole to total depth and sets out a system whereby the financial implications of investment into a new technology can be assessed by comparing three strategies. The best scenario for return on investment and increased profitability can then be chosen. The study deals with the economic analysis, risk analysis and the methodology used in achieving the final results. These results compare the three strategies on the basis of numerical values of drilling operational costs and production. Introduction In order to reduce well costs and thereby effectively allocate exploration funds from the exploration portfolio the industry is looking for a low cost drilling method which is currently being envisaged by the emerging slim hole drilling rig technology. This according to companies that have used this type of technology can give attractive cost advantages over conventional drilling technology. It is also felt that further micro savings can be gained, if the same wells were to be drilled using a coiled tubing drilling system but this would require the development of new technology with large costs involved. In today's business environment in order that any new technology of this nature can grow quickly through the development stages it is generally accepted that financial support must come from the oil companies i.e. "customer driven projects". The motivation for such support and the eventual investment into new technology must be to have such technology earlier than it would be normally available without the financial support and to have some form of investment recovery. In addition to this the other advantage for investment into such technology is that the technology can be tailored to what the company really requires. NEW TECHNOLOGY With any new technology it must be proven that it is either more economically efficient or technically superior in order to be competitive with current options and whilst the technical aspects are easy to establish for the engineer, the economic efficiency can present a different set of problems. In developing a conceptual project for coiled tubing drilling it was felt that a system had to be devised whereby it could be proven by theoretical financial risk assessment that investment into new technology was to the company's advantage and where such technology could be best placed and utilised to its best advantage over conventional technology. In establishing criteria for such a system it was assumed that coiled tubing drilling technology can reduce the drilling operative costs. The options considered for the economic of new technology were considered to be involvement in the following :No investment in new technology and continued use of conventional technology using the traditionalists approach. P. 429^

This paper was prepared for presentation at the 1999 SPE/ICoTA Coiled Tubing Roundtable held in Houston, Texas, 25–26 May 1999.