Abstract

Wettability of CO2–water– reservoir rock system is a key factor to determine fluid dynamic and storage capacities in CO2 geo-storage process. Despite the past researches on this matter, the parameters that influence the CO2–water–rock wettability variation are still not fully understood. One of these parameters is rock-total organic content (TOC). Thus, here, we investigated the effect of TOC on the CO2–water–sandstone wettability and the implication for CO2 geo-storage at relevant reservoir conditions. The used sandstone samples were retrieved from the South West Hub CO2 capture and storage project (GSWA Harvey 1) in Western Australia. Here, we measured the contact angles for a range of sandstone TOC (i.e. 0.01 wt %, 0.015 wt %, 0.017 wt %, and 0.019 wt % TOC) at various pressures (5 MPa, 10 MPa, 15 MPa, and 20 MPa) and at an isothermal reservoir temperature (334 K). The results indicate that both of the advancing (θa) and receding (θr) contact angles for all tested sandstones increased with an increase in pressure TOC, implying the system turned to be more CO2-wet (e.g. the advancing contact angle increased from 92° to 118° when the sandstone TOC increased from 0.01 wt % to 0.019 wt %, at 20 MPa and reservoir temperature). Furthermore, our results indicate that the sandstone contact angle increase with pressure for all tested TOC values. Thus, we conclude that minute increasing in TOC can increase the sandstone contact angle and thus decrease the residual trapping capacities. Our results suggest that the contact angle measurement of rock retrieved from reservoirs should be treated properly for TOC to have an accurate estimation for the CO2 storage capacity.

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