Petroleum Engineering

Biography

Biography: Nejat Rahmanian

Abstract

The continued rise of CO₂ emissions threatens life on Earth, through warming the planet. Carbon Capture and Storage (CCS) is an effective method in reducing CO₂ emissions, thus over time, inhibiting the effect of global warming. One of the major challenges that face the transportation process, an intermediate stage between capture and storage, is potential flow assurance issues, especially hydrate formation due to the presence of impurities such as N₂ and H₂O. If the conditions within the pipeline are at a high pressure and low temperature, hydrates could form. Hydrate formation, which is the physical combination between a gas molecule and water molecules, could cause pipe blockage and therefore, stop the high-CO₂ mixture being transported to its storage location.

This study aimed at investigating the impact of impurities on the formation of CO₂ hydrates, whilst simultaneously, considering the vapour-liquid equilibrium (VLE) phase envelope. Initially, a sensitivity analysis on binary and tertiary systems was conducted, based on the impurities most commonly encountered in CCS. Where from here, investigation into two case studies (Cortez and Sheep Mountain Pipeline) was conducted. The results from the binary analysis showed H₂S caused a significant expansion of the hydrate stability zone (HSZ). The presence of the impurities, COS, SO₂ and NH₃, caused the opposite effect to what was found with H₂S. Each impurity caused an effect on the VLE phase envelope with H₂ and N₂ causing the most significant expansion. The tertiary system sensitivity analysis showed there was a clear interaction between H₂S with Ar, O₂ and CH₄. Analysis into the case studies showed the presence of H₂S reduced the hydrate formation pressure thus increasing the likelihood of hydrate formation. This was proven to be counteracted with the presence of either COS, SO₂ or NH₃, where they increased the hydrate formation pressure.