Cyclic CO2 – H2O injection and residual trapping: Implications for CO2 injection efficiency and storage security

Abstract

To meet the Paris Agreement target of limiting global warming to 2ºC or below it is widely accepted that Carbon Capture and Storage (CCS) will have to be deployed at scale. For the first time, experiments have been undertaken over six cycles of water and supercritical CO2 injection using a state of the art high flow rig recreating in-situ conditions of near wellbore injection into analogue storage reservoir rocks. The results show that differential pressure continuously increases over multiple injection cycles. Our interpretation is that multiple cycles of injection result in a reduced effective permeability due to increased residual trapping acting as a barrier to flow resulting in reduced injectivity. This is supported by numerical modelling and field observations that show CO2 injectivity and its variation over time will be affected by multiple cycles of injection. These results suggest that loss of injectivity must be incorporated into the injection strategy and that careful management of cyclic injection will create the opportunity to increase residual trapping.

Enabling large-scale hydrogen storage in porous media – the scientific challenges

“…In turn, the capillary forces controlling residual trapping also control the imbibition and drainage behaviour of the rock, and hence the relative Please do not adjust margins Please do not adjust margins permeability. It should be noted that the relative permeability may change over time, as a result of the multiple cycles of hydrogen injection and reproduction, as seen in CO2 flow experiments 39 . There are very few relative permeability and capillary pressure measurements for the hydrogen-brine system.…”

“…However, very little is known about the influence of hydrogen on wettability. As wettability behaviour is crucial for hydrogen retention, more research is needed to identify if hydrogen influences rock wettability and what could be the potential impact of cyclic injection and extraction on wettability, as observed during CO2 storage 39 .…”

Capillary Trapping of CO2 in Sandstone Using Low Field NMR Relaxometry

“…Studies of cyclic injection regimes, which are also known as water alternating gas injection, have mostly been concerned with oil-gas-water systems in the context of enhanced recovery (Oak, 1990;Suicmez et al, 2007). However, there are several examples of cyclical injection regimes for enhancing CO 2 capillary trapping (e.g., Edlmann et al, 2019;Herring et al, 2016;Ruprecht et al, 2014;Saeedi et al, 2011), which all indicate that the total amount of CO 2 trapped increases under such an injection regime. This was also the case observed in the current study, with each injection cycle leading to a greater volume of trapped CO 2 , as shown by the increasing residual nonwetting phase saturation in Figure 7.…”

“…Numerous experimental studies have measured capillary trapping of CO 2 in rock cores (e.g., Angerer et al, 2014;Iglauer et al, 2011;Krevor et al, 2015;Ni et al, 2019;Niu et al, 2015;Pentland et al, 2011); several have also identified water alternating gas injection (Edlmann et al, 2019;Herring et al, 2016;Saeedi et al, 2011) and injection of foaming agents (Adebayo, 2018) as viable methods that increase the volume of capillary trapped CO 2 . Although the wettability of CO 2 is a critical factor controlling capillarity in such experiments, the assessment of CO 2 wettability under core flooding conditions remains an experimental challenge.…”

Low-carbon GeoEnergy resource options in the Midland Valley of Scotland, UK

“…The technology for gas injection and storage in porous media is well established. Gas is injected into a porous and permeable reservoir formation, such as an aquifer or a depleted hydrocarbon field, via injection wells, and displaces the in-situ pore fluid, usually brine, and spreads out underneath an impermeable caprock (Mouli-Castillo et al, 2019;Heinemann et al, 2018;Edlmann et al, 2019). Since thick salt formations are absent in the Midland Valley, storage in porous media has to be investigated.…”