Abstract
Conventional subsurface reservoir candidates for CO2 Sequestration are usually just deeper than 800 m to ensure CO2 is injected at supercritical state, typically these are shallow, gently dipped, low pressure saline aquifer or completely depleted and abandoned hydrocarbon reservoirs. However, in this study within the western desert of Egypt, none of the reservoirs are abandoned and the saline aquifers below 800 m are too tight with no injectivity. So, the only way was to target ultra deep saline aquifer deeper than 3 km with virgin pressure of more than 5000 psi. These ultra deep aquifers are usually highly titled, surrounded by major faults, and highly saline and those factors act against the typical trapping mechanisms for CO2 sequestration such as structural trapping, residual trapping and CO2 solubility. In this case study, we present a novel approach that relies on innovative technology to solve this unconventional challenge to sequester 0.5 Mton CO2 per annum in ultra deep saline aquifers and open the pathway for carbon storage in unconventional storage sites.
The applied approach is divided into three phases. Phase one is site screening to automatically identify the best possible sites for CO2 storage based on a scientific scorecard. Then in Phase two, dynamic simulation of the injected supercritical CO2 plume movement within the formations while honoring advanced trapping mechanisms such as CO2 trapping due to residual trapping and dissolution in saline water. Then the dynamic reservoir simulation models are fully coupled to 3D geomechanics models to study the impact of the injection on the well integrity, cap rock integrity as well as fault reactivation and integrity. Finally in Phase 3, an economical surface facility configuration and pipelining scenarios that fit the subsurface sites’ requirements.
It was concluded through an ensemble of geological scenarios that safe CO2 trapping mechanism can be increased by 30% using a time and rate managed sequential injection scheme starting from the bottom of the formation and upwards. the dynamic simulation results show that this technique helps increasing the contact area with the saline water while leveraging high pressure to overcome low solubility in highly saline water and creating convective water density currents, hence increasing CO2 solubility in water as well as residual trapping of CO2 even in structurally marginal sites.
The followed scientific approach unlocked the potential for CO2 sequestration in ultra deep saline aquifers within the western desert to be deployed for a long-term and safe sequestration of CO2 while accounting for the complex subsurface structure to pave the way for future successful CCS projects in similar environments.
