Deepwater Pipeline Pre-Commissioning Operation Using Large Diameter Coiled Tubing Instead of Standard Downline: State of the Art of This Technology
Authors: Rodrigues Vinicius , Delgado Eduardo , Frotte Adriano 
Published: March 2019

Deepwater fields present challenges to the pre-commissioning of the pipelines responsible for transporting oil and gas. Hydrostatic pressure exerted by long water columns to the downline system must be addressed and overcome because it can collapse the downhole equipment that had previously been used only in shallow waters. With the development of deepwater fields, coiled tubing (CT) provides several advantages over regular downlines. Considering that the pipelines are longer than 200 km and larger than 20 in. diameter, months of continuous work are necessary during their pre-commissioning; consequently, higher flow rates are required to reduce time and costs.

Large-bore CT as downline has proven to be a cost-effective and reliable means to access deepwater pipeline pre-commissioning. With reduced layout and costs, as compared to regular downline systems, CT can provide the only economically feasible solution for some scenarios.

To extend CT life without compromising its integrity and the operation, on-site pipe management and high cycle fatigue studies were conducted. A multi-skilled crew also helped to reduce personnel on board for a small vessel application without reducing health, safety, and environment (HSE)/service quality (SQ) levels. Customized and reduced equipment layout was implemented to address deck load and space restrictions.

The use of a regular downline dramatically affects costs because several external layers must be added to provide suitable collapse pressure resistance, increasing its diameter and requiring a larger storage reel in accordance with minimum bending radius (MBR) to avoid damage to the downline, compromising deck layout. Complex manufacturing increases procurement costs and timing, and makes on-site repair capabilities impossible. However, 3.5 in. CT considerably reduced the final operational time, reducing friction pressure losses while maintaining a feasible layout.

Improvements made on rig-up and operational procedures, as compared to previous similar project experience, enhanced technology advantages and reduced the deployment and recovery time needed. Because of vessel limitations with rough weather conditions on this project, the CT eventually had to be recovered to the surface. Consequently, these improvements reduced rigging time and safely extended the operational window, enabling multiple deployments, even within shorter intervals of fair weather.

An optimized deck layout for CT and monoethylene glycol (MEG) collection spreads was necessary for small vessel use; it reduced customer costs, considering that a much larger vessel was simultaneously operating on the other pipeline end for the largest high-pressure dewatering spread ever installed on a vessel for a pre-commissioning operation. The CT control cabin was placed perpendicularly to the reel; consequently, a closed-circuit TV system was mounted behind the reel to allow pipe spooling.

Brazil's largest and deepest pre-commissioning operation was performed safely with service quality excellence, increasing efficiency levels of the industry within this scope of work. Several lessons learned have been assessed for further improvements.