Abstract

Coiled Tubing (CT) equipment in the Norwegian sector of the North Sea has traditionally been heavy, due to CT reels using larger sizes of CT - a trend also observed in other areas. Due to the requirement of performing well interventions in longer wells and larger completion sizes, CT drums weighing 40–60 t have been utilised. Not many platform cranes are capable of lifting such heavy CT drums and during bad weather periods operations are often delayed, even when using significantly lighter CT drums. Using spoolable CT connectors allow for a long and heavy CT string to be lifted on board of a platform on two or more separate drums and joining them together again once onboard. More than 50% weight reduction has been achieved making operational schedules more predictable. In the geographical areas considered, spoolable CT connectors have outperformed traditional methods like boat spooling and butt-welding from a safety, operational and economical point of view.

Due to the reduction in weight, larger CT sizes have become available on older platforms as well. New CT applications that were previously considered unfeasible, like selective, high-rate acid fracing through CT, have been performed, extending the capabilities of CT interventions beyond previous logistical and technical limits. Being able to select the correct size of CT, with less dependency on offshore crane limits and weather has a fundamental impact on the usage of CT in the offshore industry.

Rather than discussing the spoolable CT connector itself, the primary intention of the paper is to re-view case histories that were performed during the last 5 years. Operational challenges that have been mastered, successes, failures and further developments are presented. A new CT reel configuration to simplify spoolable CT connector installation will be presented. The new applications made possible by this technology and their economic impact on the Norwegian CT market since year 2003 will be reviewed.

Introduction

Reducing the weight of CT reels has been an ongoing objective, especially in the offshore CT industry. Several methods have been established, ranging mainly from reducing the CT size itself, butt-welding, spooling the CT from a boat to the offshore installation or using split-reel systems (drop in drums). The trend to larger CT sizes observed in many markets during the recent years clearly demonstrates the desire not to compromise on the CT size itself. Especially in markets using larger sizes of CT, split-reel systems have become the standard during day to day operations. Butt-welding and spooling of CT from a boat to the offshore installation has a substantial track record for CT sizes of usually up to 2". All of these methods have their advantages and disadvantages mainly circling around issues like economic feasibility, required special resources for implementation, offshore logistics, operational flexibility and reliability.

The development of the spoolable CT connector has been described in previous publications [H.B.Luft et al, 2004]. Field implementation has been successfully performed [L.Link et al, 2005] in the Norwegian and Danish sectors of the North Sea as well as adding new types of CT applications to the conventional CT offshore market [K.Ormak et al, 2003]. The track record established for the spoolable CT connector during the last 5 years in the Norwegian sector of the North Sea clearly indicates acceptance from the operators. It has been recognised as a method of further reducing the lifting weight of CT reels and reliably performing CT operations using larger sizes of CT. Using this method CT strings have been lifted onboard the offshore installations in two or more sections (2 or more CT drums) and joined together using the spoolable CT connector.

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