Abstract

In 1997, Statoil and Halliburton Energy Services, Inc. began jointly evaluating technologies that could be used to develop a revolutionary coiled-tubing and well-intervention system. This system, which will be deployed initially in the Norwegian sector of the North Sea, sets a new standard for drilling with conventional drilling rigs or coiled-tubing drilling units. The advanced well-construction system consists of a digitally controlled and automated coiled-tubing drilling system that uses a new advanced composite coiled tubing (ACCT) with embedded wires and a tractor-driven bottomhole assembly (BHA). This system enables the geological steering of complex, extended-reach wellpaths that were not previously achievable. This paper discusses a joint development project in which the operator and the service company worked together to design a fit-for-purpose system that met Norway's stringent health, safety, and environment (HSE) requirements. The system's three major subsystems are discussed: the digitally controlled and automated surface equipment, the 2 7/8-in. ACCT with embedded wires, and the drilling and intervention BHA. Test results from qualification and pilot wells are also included.

Introduction

Statoil and Halliburton entered the development process for the Anaconda system with the primary goals of reducing drilling costs and optimizing the position of the wells to enhance production. The hostile environment of the North Sea presents several offshore drilling challenges. The Norwegian government and Statoil emphasize safety, and their statutory HSE requirements for offshore wells are among the industry's most stringent.

Feasibility

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:

  1. the dependence on steel tubulars for conveying formation and downhole sensors, drilling tools, and hydraulic fluids, and

  2. the low bandwidth of conventional mud-pulse telemetry for transmitting downhole measurements.

The concept that arose out of the feasibility study overcame these obstacles by embedding power and telemetry wires within the ACCT umbilical. This composite tubing is much lighter than steel tubing, exhibits excellent bending fatigue, has high tensile strength, and a high burst rating. It also becomes neutrally buoyant in mud weights typical of many North Sea fields, which results in reduced drag while enabling longer reaches and extended steering than could be achieved with steel tubing.

The embedded conductors provide power, data telemetry, and control of the downhole tools without the need for expensive batteries, downhole memory, downhole processing, or slow simplex mud-pulse telemetry. These conductors enable the downhole sensors to transmit all raw data collected by the downhole sensors to the surface where any number of surface computers can process the raw data into engineering units. To preclude the inevitable problems of making up wired jointed tubulars, team members determined that a reeled system would be most appropriate.

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