Direct Air CO2 Capture (DAC) is a promising negative emission technology. The main challenge associated with DAC is the high energy and material requirements, which results in a relatively high cost and may limit its environmental benefit. Steam-Assisted Gravity Drainage (SAGD), most established in situ recovery approach for Alberta oil sands reservoirs, leave a considerable amount of energy under the ground at the end of their life. The objective of this work is to investigate the energy and environmental viability of exploiting the abandoned thermal energy from oil sands reservoirs to generate DAC energy requirements. This work focuses on a unique concept of integrating DAC with SAGD after the cessation of bitumen recovery to recover energy from the reservoir and use this to supply energy for DAC. The retained energy in reservoirs can be extracted by water circulation. The recovered hot water is sent to surface energy extraction unit to generate power and heat energy. CO2 captured from the atmosphere is then transported by pipeline and sequestered in a suitable geologic reservoir. To conduct our analysis, we create an energy balance on the coupled system and calculate the life cycle carbon balance with the goal of creating a stand-alone, carbon-negative CO2 capture system.
We consider the electrical and thermal energy for CO2 capture in the range of 100-600 tCO2/day using a solid-based DAC process, in which the loaded sorbents are regenerated at a temperature of 90-105 °C. An isobutane Organic Rankine Cycle (ORC) is utilized to generate electricity from a geofluid circulated in post-SAGD heat recovery process with the temperature varying from 130 to 170 °C. The heat required by the DAC is extracted directly from the produced geothermal fluid. The analysis uncovers that Direct Air Capture and post-SAGD reservoir can be combined in a stand-alone power island to capture up to 284.5 tCO2/d at 130°C and 427 tCO2/d at 170 °C geofluid surface temperature assuming deploying the technique in 40 production wells.
Furthermore, our modelling results show that CO2 capture efficiency for abovementioned ranges of capture rate and geofluid temperature varies between 70-99%. For no external energy demand, CO2 capture efficiency touches 99% but as the external sources of energy is being involved, the efficiency declines to a minimum of 70%. This study presents a novel concept for using the waste heat in oil sands reservoirs to provide DAC energy.