Historically, well drilling operations have been based exclusively on steel pipe. Recently a well construction system that incorporates composite coiled-tubing technology has been introduced. This paper examines this system and its implications for the future, with specific emphasis on composite issues: the pipe and connectors. This revolutionary full-system development encountered numerous challenges, many of which are related to the unique properties of composite pipe in difficult hole conditions. The technological solutions to these challenges are examined in depth.
This new technology, originally developed by Halliburton and Statoil and called the Advanced Well Intervention System (AWIS, Fig. 1), is based on breakthrough advances in composite materials, telemetry, and system-control sciences. Halliburton and Statoil originally planned this unique technology to develop inaccessible reserves in Statoil's mature North Sea Fields. In less than 27 months, from the feasibility study in late 1997 to completion of an extensive testing and qualification program in early 2000, Halliburton and Statoil produced this complete fit-for-purpose, digitally controlled system that uses Advanced Composite Coiled Tubing (ACCT, Fig. 2), a carbon-fiber composite umbilical with embedded conductors, and a bottomhole assembly (BHA, Fig. 3).
During an extensive feasibility study, team members challenged each other to not be bound by traditional thinking in the development of a new concept. Before the new concept could be developed, the following obstacles had to be identified:
the dependence on steel tubulars for conveying formation and downhole sensors, drilling tools, and hydraulic fluids, and
the low bandwidth of conventional mud-pulse telemetry for transmitting downhole measurements.
The concept that arose from the feasibility study overcame these obstacles by embedding power and telemetry wires within the ACCT umbilical. Additionally, to preclude the inevitable problems of making up wired jointed tubulars, team members determined that a reeled system would be most appropriate.
When the feasibility study was complete, a development team was tasked with turning the vision into reality. The multinational team was composed of personnel based in Norway, the United States, and Great Britain. Technical expertise included petroleum engineering, mechanical engineering, electrical engineering, technical safety, and health, safety and environment (HSE). In addition, user groups representing coiled tubing, drilling, and logging operations contributed to the functionality of the final system.
The end result was a system that combines exceptional safety and design features with technology that allows the transmission of real-time bottomhole data through the embedded wires in the ACCT. The remotely operated AWIS minimizes human/machine contact and dramatically reduces the chance of accident or injury. The real-time monitoring capabilities, a unique tractor-driven BHA, and a 3D steering device allow the ACCT to reach and be maneuvered into hydrocarbon pockets that would previously have been inaccessible. Exploiting these previously unreachable reserves would minimize cost-per-barrel and extend the life of the field.