Integrated Fluid and Heat Flow Model: Analyses and Operation of Subsea CO2 Injection System

The required CO2 injection rate for carbon capture and storage (CCS) to meet the net zero ambition is significant. Deepwater (subsea) environments provide the potential for high rate, sustained injectivity and low well count. The subsea system is characterized by huge volumes of flowline and riser, relative to the well. Deepwater subsea environments are also characterized with high pressure and low temperature.

In this research, we developed and validated a one-dimensional (1D) finite element model to analyze the non-isothermal fluid flow behavior of the integrated deepwater system that is comprised of surface, subsea and subsurface components.

For improved efficiency, optimal storage density and operational stability, the desire is to inject CO2 at supercritical state, maintain dense phase in the entire system, avoid flash vaporization at any point along the system and during injection operations. The developed model demonstrates the feasibility of integrated subsea systems to meet these desired criteria.

We conclude that for subsea systems, dense phase is maintained throughout the entire system over the range of depleted to geopressured reservoirs, high to low injectivity, various subsea geometry (riser, flowline length, pipe diameter) and during ramp-up operations.

In the subsea system, the potential for flash vaporization is highest at the subsea wellhead under high injection rates. Frictional pressure drop is a crucial (non-linear) factor that exacerbates the liquid-vapor phase transition in deepwater (subsea) systems. This is contrary to onshore or shallow water development where flash vaporization is dominant for depleted reservoirs.

The scenarios, cases and analyzed results from simulations conclusively support the objectives of this research. Deepwater (subsea) CCS is feasible and has technical and environmental benefits, relative to onshore and offshore environments. Prudent and proactive research to enable CCS in deepwater (subsea) must be advocated.