Phenomenological study of unstable two-phase CO2 flow in a pipeline system

CO2 transportation by pipeline is a fundamental enabler for the large-scale deployment of carbon capture and storage (CCS) networks across Europe towards 2040. While there is significant industrial experience transporting CO2 in liquid form, new challenges arise in the Norwegian Continental Shelf (NCS). Approximately 30% of the estimated storage capacity lies in depleted natural gas fields, which are characterized by relatively low reservoir pressures. Under such conditions, CO2 may need to be transported as a two-phase gas-liquid mixture. This two-phase flow transport regime has only been minimally investigated and remains a largely uncharted research area. Two-phase flow can give rise to strongly unstable behavior, posing risks to the integrity of injection wells and the wider transport system. Experimental studies carried out as part of this project have now provided evidence of the potential occurrence of two-phase flow instabilities under some studied conditions. However, the underlying physics triggering these instabilities remain under investigation as part of the project. Understanding two-phase CO2 flow instabilities is key to ensuring the safe and cost-effective expansion of CCS networks.

Potential CO2 storage locations in the Norwegian Continental Shelf, NCS, are in saline aquifers and in depleted fields. The latter represents about 30% of the potential storage capacity. Existing CCS projects are based on storage in saline aquifers at hydrostatic-pressure in which the well-known experience in transporting dense phase CO2 can be applied. However, due to the low pressure, the storage in depleted reservoirs may require transporting CO2 in a two-phase state, which is an uncharted area. In this context, there is an important lack of understanding related to potential flow instabilities during the transport of CO2 in pipelines at two-phase flow conditions. This causes serious concerns about the maturity of the computational models for designing, analysing and operating the future CO2 pipeline infrastructure. This project focuses on closing important knowledge gaps on two-phase flow instabilities and transient phenomena in CO2 pipeline systems. The success of this project is of great relevance for minimizing the risks related to CCS operations and new developments, in addition to enabling the access to the more than 30% of storage capacity represented by depleted fields and thus contributing to the Norwegian goal of cutting domestic emissions by 50-55 precent by 2030. The work proposed in this project will fill in the knowledge gap by generating benchmark data from three highly specialized experimental facilities in Norway. The unique data will enhance our understanding, the physics of instability phenomena related to CO2 systems, and significantly improve the quality of simulator models.