A system design approach for thermal insulation of subsea equipment using CFD

Subsea oil and gas production systems are becoming more complex and more automated. At ocean depths down to 2300m reliability and dependability are of utmost importance. During a production shut-down the production fluid in the subsea equipment will be cooled off by the surrounding ocean water. Simultaneous presence of light hydrocarbons and water in a cold environment with relatively high pressure can create hydrates that are ice like substances capable of blocking the production piping and prevent fluid flow. The equipment is therefore thermally insulated to slow down the cooling process. Field operators are challenging subsea equipment makers to break new boundaries with respect to passive thermal insulation and to increase reliability of the thermal performance. This paper will present the methodology and results of a thermal insulation design project conducted for Total E&P Angola. The project aimed to meet cool down times in excess of 20 hours in areas where 8 hours were previously the norm. In order to meet such a stringent requirement, a system approach to thermal design had to be adopted and reliance on computational analyses tools had to be strengthened. Following a design phase in which the computational analyses tools CFD and FE were used to design the thermal insulation, a full scale cool down test was performed with a subsea Manifold. The simulated cool down results generated by CFD and FE compared well to the results of a full scale cool down test.