Wet insulation. There are now several advanced wet insulation materials available for different subsea applications, such as solid polymers polypropylene (PP), novolastic, polyurethane, and syntactic foams glass syntactic polyurethane (GSPU). They can achieve low U-value for heat retention in subsea flowline systems including jumpers and hardware. The wet insulation is directly coated to steel pipes and placed on the seabed exposed to seawater. It is typically tailored to withstand compression due to hydrostatic head in deep water. It offers good mechanical properties along with an extended track record in the offshore oil and gas industry. Wet insulations are available in several forms, such as 3-layer, 5-layer and 7-layer consisting of FBE, adhesive foam PP, insulation materials, and an outer shield.
Pipe-in-pipe (PIP) insulation. For heavy oil production, PIP insulation can provide better heat retention to maintain fluid temperature above the safety margin of hydrate and wax temperatures during normal operation achieving lower U-Values (~ 1.0 W/m2-K or less) and high insulation performance. It also offers a significant reduction to both material and installation costs. Such insulations have been tested at deep water depths. In PIP, a pipe is inserted inside another pipe. The created intermediate annulus is used to hold a dry insulation material which is protected by the outer pipe from hydrostatic pressure and water penetration. In PIP insulation, the inner (carrier) pipe is insulated with a low conductivity dry insulation such as aerogel or low density polyurethane foam. The outer pipe is typically steel or polyethylene, depending on applications. In case a rigid outer pipe is required, an air gap exists between the outside diameter surface of the insulation and inside diameter of the outer pipe. The effective conductivity of the air gap is reasonably low and adds to the heat resistance of the system.
Other innovative methods. Other technological advances to address flow assurance problems include: cold flow technology for un-insulated pipe, collapsible pipe, coiled tubing remediation, phase change insulation, internally insulated corrosion resistance pipeline, and flow optimized system architecture with limited applications.
Non-chemical solutions can be applied safely in thermal management of hydrate and wax problems for subsea field developments. When the flowline production system including water stops and subsea hardware are not insulated adequately, cold spots may lower the temperature substantially and enhance the risks of hydrate and wax formations/depositions. Application of PIP insulation combined with wet insulation can prevent such risks effectively and reduce capex/opex by minimizing the use of chemical inhibition, pigging frequency, and depressurization. Even in PIP flowline/flexible riser production systems all subsea jumpers, structures, equipment, and water stop assembly involved should be insulated adequately to maintain fluid temperature above the hydrate and wax formation temperatures. The combination of chemical inhibition, depressurization, pigging, and dead oil circulation can help reduce opex for economical operation of the subsea production system throughout the life of field.
To see the full version of this article, please go to:http://www.offshore-mag.com/articles/2014/03/non-chemical-products-offer-effective-flow-assurance-solutions.html.
Keshawa Shukla, Ph.D., is senior manager of flow assurance engineering and global subject matter expert at McDermott in Houston, Texas.
The author wishes to acknowledge the McDermott business development teams in Houston and London, and the subsea engineering group for supporting this publication. Special thanks go to Miranda Smith and Jason Martinez.