Qualification of Flexible Dynamic Risers for Supercritical CO2

Abstract

Abstract In the oil and gas industry there is a growing demand for riser solutionsdedicated to high partial pressures of CO2. Part of this demand is driven bydeep water high pressure reservoirs with high CO2 content. In addition there isa growing interest in reinjection of CO2. The reinjection can be driven by adesire to reduce CO2 emission as in Carbon Capture and Storage (CCS) projects, but also as a way of Enhanced Oil Recovery (EOR). In all cases it is likelythat CO2 will be present at high pressures and in its supercriticalphase. NKT Flexibles is about to complete a three-year documentation and qualificationprogram with the aim of qualifying a broad range of flexible pipe solutions foruse with supercritical CO2 (SCCO2). An important part of the program has beenmaterial qualification. For polymeric materials, the main challenge is the highsolubility in some polymers of supercritical CO2. This leads to potential highswelling and a risk of mechanical damage (blistering) in explosivedecompression situations. Furthermore, supercritical CO2 has a strongextraction power which may result in rapid loss of plasticizer in plasticizedpolymers. The qualification program included a broad variety of tests qualifying againstpotential failure mechanisms. The testing program is executed on polymers incontact with the bore stream. Results show that cross-linked poly-ethylene(XLPE) inner liner has superior resistance to SCCO2 on all tested parameterscompared to other available liner materials. For steel materials, the main potential risk when exposed to supercritical CO2is corrosion. High CO2 content together with water forms a corrosiveenvironment which could have some impact on the metals used. For flexible pipeapplication, this is primarily relevant for the carcass material and endfitting which is in direct contact with the bore stream. Selection ofappropriate metallic materials will be based on the actual specification of thebore stream. This paper will present the full scope and results of the qualification workcompleted for qualification of flexible dynamic risers for SCCO2. Introduction For the last 35 years, unbonded flexible pipes have been a key component inoffshore oil and gas production. They represent an alternative solution torigid steel pipes where they have the advantages of faster installation timesand better adapting potential for changes in field layout. These advantagesoften make unbonded flexible pipes a more economical solution than rigid steelpipes.