CO₂wettability of seal and reservoir rocks and the implications for carbon geo-sequestration

Abstract

We review the literature data published on the topic of CO 2 wettability of storage and seal rocks. We first introduce the concept of wettability and explain why it is important in the context of carbon geo-sequestration (CGS) projects, and review how it is measured. This is done to raise awareness of this parameter in the CGS community, which, as we show later on in this text, may have a dramatic impact on structural and residual trapping of CO 2 . These two trapping mechanisms would be severely and negatively affected in case of CO 2 -wet storage and/or seal rock. Overall, at the current state of the art, a substantial amount of work has been completed, and we find that:Sandstone and limestone, plus pure minerals such as quartz, calcite, feldspar, and mica are strongly water wet in a CO 2 -water system.Oil-wet limestone, oil-wet quartz, or coal is intermediate wet or CO 2 wet in a CO 2 -water system.The contact angle alone is insufficient for predicting capillary pressures in reservoir or seal rocks.The current contact angle data have a large uncertainty.Solid theoretical understanding on a molecular level of rock-CO 2 -brine interactions is currently limited.In an ideal scenario, all seal and storage rocks in CGS formations are tested for their CO 2 wettability.Achieving representative subsurface conditions (especially in terms of the rock surface) in the laboratory is of key importance but also very challenging.

Measurement and modelling of interfacial tension in methane/water and methane/brine systems at reservoir conditions

“…IFT can affect water-gas contact movement and distribution of hydrocarbons in a reservoir, water alternating gas drive, gas-injected enhanced oil recovery processes and multiphase flow calculations [1]. Injecting and storing acid gases like carbon dioxide and hydrogen sulphide separated from sour natural gas into reservoir has grown interest in the past decade [2,3] and the accurate knowledge of this property is also of key importance for the efficient and economical design of potential processes. Reviewed data can be found in the works of Schmidt et al [4], Rushing et al [5], Shariat et al [6] and Pereira et al [7] and references within.…”

On sorption and swelling of CO2 in clays

“…In addition, CO 2 exhibits specific wetting behaviour, and incomplete water-wetting conditions have been reported. Moreover, wetting properties may be altered by water-rock-interactions (Iglauer et al 2015), potentially affecting two-phase flow in the reservoir and capillary sealing of barriers.…”

A statistical analysis of the effects of pressure, temperature and salinity on contact angles in CO 2 –brine–quartz systems

“…Quartz is often the dominant mineral in sandstone , and many of the units targeted by geosequestration feature quartz as the main component (see Table 3 in Iglauer et al, 2015). The wettability of quartz is of interest because it affects residual capillary trapping, which is one of the main mechanisms for the long-term geological storage of carbon dioxide (Iglauer et al, 2009;Akbarabadi and Piri, 2013) and is most effective in water-wet reservoir materials (Tanino and Blunt, 2012;Iglauer et al, 2012;Choudhary et al, 2013).…”