Because of the length of the offshore pipeline, the temperature of the CO2
would be (at worst case) seabed temperature in winter. Injection of cold (5 °C) liquid CO2
into a hot (57 °C) formation has the potential to result in thermal fracturing, which in turn can result in instability for inflow performance and, if the fracture should extend vertically, result in loss of well integrity for long term storage of CO2
Key objectives of the perforation strategy were to:
- Ensure well integrity
- Ensure fracture growth remained within the reservoir
- Allow injection of the required volume of CO2
- Allow re-perforating or additional perforating to take place at a future data.
A fracture model assessed the impact of injection of the cold CO2
into the hot formation including thermoelastic and poroelastic effects.
The results indicated that the predominant change in the effective stress was due to thermal influences resulting in fracturing of the near wellbore.
Perforation intervals were then defined based on minimizing the thermal fracturing and ensuring that injectivity could be achieved predominantly through the matrix thus maximizing integrity and minimising flow instability.