Qualification of Polymer Materials for High Pressure CO2 Flexible Pipe Structures

Abstract

In the oil and gas industry there is a growing demand for riser solutions dedicated to high partial pressures of CO 2 . The demand is primarily driven by deep water high pressure reservoirs with high CO 2 content. In addition there is a growing interest in reinjection of CO 2 . The reinjection can be driven by a desire to reduce CO 2 emission as in Carbon Capture and Storage (CCS) projects, but also as a method for Enhanced Oil Recovery (EOR). In all cases it is likely that CO 2 will be present at high pressures and in its supercritical phase.NOV Flexibles has in recent years developed dedicated riser solutions for a broad range of flexible pipe applications for use with high pressure dense phase CO 2 also referred to as supercritical CO 2 (SCCO2). An important part of the qualification program has been material qualification. For polymeric materials, the main challenge is the high solubility in some polymers of high pressure CO 2 . This leads to potential high swelling and a risk of mechanical damage (blistering) in explosive decompression situations. Furthermore, high pressure CO 2 has a strong extraction power which may result in rapid loss of plasticizer in plasticized polymers. This paper describes the latest status and achievements in the qualification program including a broad variety of tests qualifying against potential failure mechanisms to CO 2 pressures in the range of 650 to 700 bar. The results show that peroxide cross-linked poly-ethylene (XLPE) in-line cured inner liner with a high degree of cross linking has superior resistance to high pressure CO 2 on all tested parameters compared to other available liner materials. This makes it the preferred liner material for ultra high pressure CO 2 gas risers and flowlines whereas PVDF is the optimum choice for production risers with temperatures above 90 °C and intermediate CO 2 partial pressures.

Prediction of flexible pipe annulus composition by numerical modeling: identification of key parameters

“…Besides experiments, some work is in progress in order to use SAFT (Statistical Associating Fluid Theory) [13] and PC-SAFT (Perturbed-Chain SAFT) [14] equation of states to calculate the solubility of gases inside the polymer. This approach has been successfully used in [15]. In particular, the swelling of the polymer may be considered since its mechanical confinement might lower the solubility and probably also the permeability.…”