CO2 Wettability of Sandstones: Addressing Conflicting Capillary Behaviors

• Published in: Geophysical research letters 2019-01, Vol.46 (2), p.776-782
• Main Authors: Garing, C., Benson, S. M.
• Format: Article
• Language: English
• Subjects: Anthropogenic factors; Brines; Capillarity; Capillary pressure; capillary pressure curves; Carbon capture and storage; Carbon dioxide; Carbon sequestration; Climate change; Duration; Emitters; Exposure; Flooding; Floods; Fluids; geologic carbon storage; GEOSCIENCES; Global warming; Greenhouse effect; Greenhouse gases; Human influences; Migration; multiphase flow; Pressure; Pressure data; Pressure measurement; Reservoirs; residual trapping; Rocks; Saline water; Sandstone; sandstones; Scaling; Sedimentary rocks; Stone; Trapping; Variability; Water pollution; Wettability; Wetting
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL081359

Understanding the capillary and wetting behavior of supercritical CO2 (scCO2) and brine in reservoir rocks is crucial for reliable predictions of geologic carbon storage, as it strongly impacts CO2 migration and residual trapping in the reservoir. The wetting state of such systems can be assessed through laboratory measurements of the capillary pressure characteristic curve. However, while some studies reported consistent scaling with strongly water wet systems, some others observed deviations from hydrophilic conditions. We present core‐flooding drainage capillary pressure measurements using scCO2/water and N2/water on a Berea sandstone, untreated, then fired, and then exposed to scCO2 for 28 days. The purpose is to investigate the impact of firing and longer exposure to scCO2, two potential sources for variability in experimental observations, on capillarity and wettability. The results show excellent agreement among all the core‐flooding capillary pressure data, suggesting no change in wetting state due to firing or longer exposure. Plain Language Summary Carbon capture and storage is a promising technology to limit anthropogenic greenhouse gas emissions responsible for global warming. It consists in capturing CO2 from large point source emitters and transporting it to a site where it will be injected in deep geological formations for storage. One important property of a rock in the presence of two nonmiscible fluids (here CO2 and formation brine) is the preference of one fluid over another to be in contact with the rock's surface, a property called wettability. Wettability directly impacts the way injected CO2 will flow in the subsurface and will stay trapped in the rock. However, although considerable effort has been made in the past decade to determine the wettability of storage rocks with respect to CO2 and brine, there is considerable variability in the reported data. This study focuses on two particular factors that could lead to the differences in experimental observations: the preparation of the rock sample used for measurements and the duration of exposure to CO2. We observed no change of wettability and general conditions favorable for CO2 trapping in the studied rock, a sandstone. Key Points Drainage capillary pressure measurements were repeated on a Berea core untreated, fired and then exposed to supercritical CO2 Firing the rock core does not impact the strongly water wetting state of the system No wettability alteration is observed after t