Due to the growing adoption of optical sensing technologies for system performance instrumentation in the oil and gas industry, evidence that technologies are robust and reliable is being demonstrated. This paper reports the results of tests carried out in the laboratory detailing the temperature gradient performance of a newly developed insulation material used on subsea infrastructure. Tests carried out in an environmental test chamber are presented to illustrate the sensor performance in transient temperature conditions. Results of tests during a system cool-down on a subsea tree prior to deployment of the equipment to monitor system temperatures during the cool-down cycle are also discussed. Measurements were taken as the tree was heated to an equilibrium state using circulating water.
A critical element of the subsea hydrocarbon production system is the subsea tree which sits on the wellhead and provides the interface between the reservoir and the rest of the subsea infrastructure. The subsea tree controls the flow of the production fluid from the reservoir, through the wellhead and to the rest of the subsea infrastructure, until it reaches the topside facilities used to process the production fluid.
Assuring the continual flow of fluids through the subsea tree is a vital requirement of the production process. As part of flow assurance schemes, the operator must reduce the potential for blockage of wellbore or production flowlines due to hydrates and wax forming in low temperature conditions. The effective control of an oil or gas field can require production to be stopped in the event of an emergency or dangerous conditions forming in the system. During this period of shutdown, production fluid will remain present in the flow loops of the subsea production system. The initial temperature of the production fluid will be dependent on the reservoir characteristics, but this will begin to match the surrounding subsea temperature while production is interrupted. During such conditions, temperatures where hydrates and waxes can form within the subsea system can often be reached.
Typically, insulation is used around critical items in the subsea infrastructure in an attempt to maintain above hydrate forming temperatures of the production fluid contained within the equipment during shutdown. Traditionally, insulation materials based on glass syntactic polyurethanes or neoprene based rubber materials have been used for subsea infrastructure insulation. Effective insulation is critical to give operators confidence when performing shutdown operations that hydrates will not form in the system; consequently there is considerable interest in developing improved insulation.
The emergence of hydrocarbon production systems operating at higher temperatures has also required the development of new materials that can operate at these higher temperatures and are efficient insulators, highly flexible and less susceptible to cracking. Additionally, the ability to combine insulation with in-built methods for monitoring the temperature of the fluid during shutdown offers a significant opportunity to enhance the operation of hydrocarbon production systems.
Fibre-optic sensor technology is well established and has a number of advantages over traditional electronic sensors for subsea sensing applications