Application of Insulation Materials for Deepwater Subsea Completion and Production Equipment
Authors: Janoff Dwight , Davalath Janardhan 
Published: October 2008

As oil and gas wells are being developed in deepwater, hydrate formation in the production system has become a major concern. During a production shut down, hot produced fluids become stagnant and are cooled by the surrounding cold water, resulting in gas hydrates. Such blockage can plug the bore of a subsea tree, tree piping, jumper, manifold and flowlines, causing loss of production and inability to open or close valves. Several options are available to manage hydrate formation in the seabed hardware: continuous or intermittent chemical injection, partial or full thermal insulation of all hardware or some combination. The selection of these options impacts overall flow assurance performance, capex, opex, operability and project risk.

For a thermal insulation material to perform for subsea completion and production equipment, it must have the following characteristics: low thermal conductivity, ability to retain its insulating properties under hydrostatic compression and long term exposure to sea water, ability to fit into limited available space, ease of installation and repair, ability to withstand handling impacts and corrosion protection. Trees and manifolds represent a difficult application for insulation because of the complex and irregular surfaces. Different types of insulation materials used for subsea completion equipment include epoxy syntactic foams, flexible epoxies, urethanes, and vulcanized elastomers.

This paper will present an overview of the selection and design process to manage hydrates in subsea production equipment with respect to performance, cost, operability and risk issues. For thermal insulation design, methods of evaluating the properties and assessing the long-term performance will be presented and review several examples of FMC's successful field application of this technology in water depths up to 5,000 ft. Also, the advantages and disadvantages of these materials with regard to subsea components will be discussed. This paper will also describe the status of the high temperature insulation material development for subsea production equipment, which will be required for upcoming projects.

Introduction

Options for Hydrate Management.

As drilling and production operations expand into deepwater environments, operators need to consider the potential risk of gas hydrate formation in wellbores, subsea pipelines and subsea equipment during both drilling and production operations. Specifically, this paper addresses the hydrate management options for subsea equipment such as Christmas trees and associated piping, well-to-manifold jumper lines, manifolds, manifold-to-sled jumpers, flowline termination sleds, etc. Gas hydrates are ice-like solids that form from gas and water under combinations of high pressure and moderately low temperatures. Alkane hydrates in the form of crystalline methane hydrate can form at temperatures as high as 21 °C (70 °F) at pressures of 300 bars (4,300 psi)1. This is illustrated in Figure 1.

Figure 1. Phase Diagram showing the conditions under which hydrates will form1.(Available in full paper)

Hydrates can form at conditions to the left of the curve shown in Figure 1. At conditions to the right of this curve, hydrates will not form. Hydrate formation conditions depend on gas composition, primarily the presence of low-molecular weight hydrocarbons such as methane, ethane, propane, isobutane and normal butane and the water salinity.