Developing Operating Principles for Safe CO2 Injection in Depleted Gas Fields – a Flow Assurance Perspective

Abstract

Summary Two large-scale CCS projects are planned in the Netherlands: Porthos and Aramis. EBN is a partner in both projects, which aim to inject CO2 into highly depleted offshore gas fields at pressures as low as 17 bar. This low pressure leads to operational challenges primarily driven by the risk of reaching very low temperatures in the wellbore and near-reservoir area. This risk is not present in CCS projects that inject into aquifers at much higher pressures. The Sleipner project uses a shallow aquifer at roughly 800 mTVD and around 80 bar. Other CCS projects (Snøhvit, Quest and the planned Northern Lights projects) all use aquifers deeper than 2000 mTVD, corresponding to pressures above 200 bar. EBN have performed extensive flow assurance simulations to evaluate the feasibility of injecting CO2 in low-pressured gas reservoirs. Depending on reservoir characteristics – primarily pressure and injectivity – different injection philosophies may be required in order to avoid excessively low temperatures which can pose a risk to well integrity or to the ability to inject. The most important learning from this work is that operating philosophies and low temperature risks should be evaluated on a project-by-project basis to ensure the optimal approach is used.