Whilst the combination of wet insulation systems on the risers and composite syntactic foam buoyancy can provide a cost effective solution there are situations where the minimum achievable overall heat transfer coefficient (OHTC, U Value) of standard wet insulations is inadequate for the more challenging project conditions.
Many deepwater reservoirs are relatively shallow beneath the seabed and so have low wellhead temperatures which, in turn, creates a propensity for wax deposition and hydrate formation. The limiting U Value achievable by standard deepwater wet insulation systems (approx. 3.5W/m2.k) may be inadequate to prevent excessive fluid temperature loss during seabed flowline or riser transit. However, macrosphere-free epoxy syntactic foams have massively superior insulation performance compared to deepwater wet insulation systems (0.10-0.12W/m2.k vs. 0.16-0.18W/m2.k respectively) and can also be used in essentially unlimited thickness. Pure epoxy syntactic foams can therefore offer a level of thermal insulation performance which is unachievable with standard pipeline external insulation coatings.
Balmoral has developed a family of epoxy syntactic foams which, as well as providing the required buoyancy performance for HRTs, provides ultra-high insulation performance on HRTs and seabed flowlines.
This family of materials, generically named Supatherm, is capable of providing U Values down to 2.0W/m2.k. Under normal flowing conditions, the temperature loss during the entire HRT transit will routinely be well under 1°C. Similarly, when used in a flooded bundle configuration for seabed flowlines, temperature drops of less than 1°C per kilometre have been achieved.
As Supatherm syntactic foam is directly providing the insulation performance rather than being installed external to the riser external insulation coating it is permanently exposed to seawater at the full process fluid temperature. Wellhead, and therefore riser, temperatures can be in the 80-100°C range and, at this temperature, standard epoxy resin systems used in drilling riser-type foams and distributed buoyancy-type foams are subject to hydrothermal degradation.
Supatherm is based on an epoxy resin system originally developed as a lining material for downhole tubulars operating at ultra-high temperatures of up to 140°C. Formulated as syntactic foams in the Supatherm range, the resin system provides the ultimate in hydrothermal degradation resistance to temperatures exceeding 100°C.
Cross section of modular Supatherm insulation in flooded sea-line bundle
The Supatherm system was supplied as HRT insulation/buoyancy and as seabed flowline bundle insulation on the first of the offshore deepwater Angolan developments in 2002 and continues to operate satisfactorily.
Balmoral’s unique Supatherm system is formulated to allow the production of elongate moulded shapes such as bundle and riser modules as required for combined insulation/buoyancy on sealine bundles and hybrid risers as well as more simple half-shell systems as used in the encapsulation of pipeline mid-line flanges and flange terminations to subsea structures.