Composite Choke and Kill Lines: Qualification and Pilot Installation
Authors: Skaugset Kjetil , Gronlund Per Kristian , Melve Bjorn Kristian , Nedrelid Kristin 
Published: June 2014

Choke and kill lines used on deep water drilling risers subjected to high pressure are traditionally made of heavy wall steel pipes. By introducing light weight composite choke and kill lines, the submerged weight can be reduced by 50%. Choke and kill lines for deep water and high pressure may contribute up to 50% of the total drilling riser weight.

The current development is making 22.6 m (75 ft) long composite choke and kill lines with an internal diameter of 114.3 mm (4.5") and pressure rated to 1034 bar (15000 psi). The lines have a steel liner and steel end connections to make them compatible with standard steel lines. The steel liner is reinforced with carbon fibre/ epoxy structural composite. The lines are designed to meet all relevant load cases both from operation, handling and qualification according to requirements in API and DNV standards.

A technology qualification plan has been developed after a threat assessment exercise according to DNV RP-A203. To close the gaps in the technology qualification plan a set of pipe tests (on full diameter pipe) was conducted satisfying the requirements in the relevant design documents, including burst, fatigue and creep tests. The technology qualification plan establish the degree of qualification required for the new technology and comprises all activities needed in order to provide the set of evidences needed to show that the component is fit for purpose, and shall demonstrate confidence that the manufactured C&K - lines meet all performance requirements and hence will function reliably for intended use.

To demonstrate the ability to make full length slender components by filament winding, three full 22.6 m (75 ft) lengths of the choke and kill lines were manufactured and have been successfully factory acceptance tested at 1560 bar (22500psi), i.e. 1.5 times the maximum design pressure.

One of the unknown factors identified in the threat assessment was potential handling damage. Based on the threat assessment it was decided to have a pilot installation of the technology at the desired technology readiness level. A drilling rig has been selected as the potential site for a pilot, and the pilot is closing all gaps in the technology qualification plan.

Introduction

Background

Hydrocarbon prospects are localized in water depths beyond 3000 m. At present it is a technological challenge to find cost-efficient methods to develop these potential ultra-deep water oil reserves found. Typical ultra-deep water areas are Gulf of Mexico, offshore Brazil, West Africa, East Africa (Kenya, Tanzania, Mozambique), Indonesia and India. Even more challenging is the ultra-deep water areas with harsh environment; these are Canada East Coast, Atlantic Margin and Norwegian Sea.

The subsalt (or presalt) reservoirs adds increased complexity of very deep wells (6000–7000 m below the sea bottom), with long casing strings that needs to be deployed in the wells. The casing string weights can also be a challenge to the hook load of the derrick system on the rig. A high pressure reservoir needs a heavier drilling fluid to balance the well pressure, which adds even more to the hook loads. The size of the drilling rig is dependent on the requirements from both drilling riser system and the casing string.

For deep water high pressure applications, choke & kill lines contribute to about 50% of the total drilling riser weight. Lighter choke & kill lines may increase the safety level by enabling use of heavier mud during drilling operations in deep water high pressure reservoirs.