Development and Application of a Novel Coiled Tubing String for Concentric Workover Services
Authors: Quigley P.A. , Nolet S.C. , Williams J.G. , Sas-Jaworsky A. 
Published: October 2008

Fiberspar and Conoco jointly developed a 1 112 inch O.D. advanced composite coiled tubing prototype for high pressure oil and gas well service. The tubing design is based upon a comprehensive set of performance specifications including: axial tensile and compressive behavior, axial and bend cycle Fatigue requirements, ultimate burst pressure, combined cyclic bending and internal pressure as well as surface wear, snubbing and external collapse specifications. The development philosophy was to utilize standard hardware for steel coiled tubing handling and injector equipment where possible. End couplings designed for easy make-up in the field were developed and advancements were made in stripper technology which are applicable to steel as well as composite coiled tubing.

A three-phase qualification approach was implemented:Sub-component testing of short-length specimens using a universal load test frame (axial tensile, compressive and Fatigue behavior) as well as combined internal pressure and cyclic four point bending tests; axial tests included room temperature and elevated temperature testing.Intermediate level testing of 40 to 100 foot long Fabricated advanced composite tubing designs using a fill-scale coiled tubing injector assembly and a modified stripper to cycle in and out of a 35 foot deep test well with 3,000 psi annulus pressure capability. Fully instrumented testing of snubbing loads, tube and annulus pressures as well as tubing strains was completed. Intermediate testing included multiple trips of specimens to investigate long-term fatigue and wear effects.Full-scale field level testing of a 1,000 foot string of advanced composite coiled tubing.

Fiberspar assembled a fill scale manufacturing line for continuous production of long lengths of advanced composite spoolable pipe. A 1,000 foot string of the selected coiled tubing design was built and spooled on a seven foot core diameter reel and successfully tested at the Halliburton Energy Services test well in Duncan, Oklahoma.

Test results demonstrated the ability to construct the novel coiled tubing product to attain the desired performance specifications at one-third the weight of conventional steel coiled tubing. The specified composite tube design provides a service tool which allows for increasing fluid pumping pressures, improved fluid flow characteristics, and greater handling capability through enhanced tube flexibility. The preliminary results of the prototype testing program demonstrate the potential for extending the service life by at least an order of magnitude beyond high-strength steel tubulars. Future applications actively being investigated for this technology include flowline remediation to remove paraffin and hydrates where the horizontal reach is predicted to be several times greater than the reach of steel products, spoolable production tubing and velocity string completions in deep and or highly corrosive wells, spoolable flowlines, umbilical systems, and risers for subsea applications.

Introduction

The use of coiled tubing (CT) for live well intervention has now become widely accepted for the economic benefits derived from its rapid deployment and short time on location. Down-time is minimized during service operations reducing cost while improving productivity.