Impact of salinity on threshold pressure of mudstone in sealing integrity processes of CO2.

Abstract:

CO₂ capture and storage (CCS) technology is a vital tool for deep reduction of CO₂ emission from large point sources (e.g., Power generations, Cement and Steel manufacturing plants etc.), and understanding of fate of storing CO₂ migration into reservoirs is significantly an important step for CO₂ geological storage safety. Several measurements of CO₂/water/solid (rock) contact angle related strongly to CO₂ migration into pores of rocks have been conducted so far. These findings indicated commonly that water wetting onto mineral surface changes in supercritical CO₂ (scCO₂) state even though using both pendant and sessile drops and its effect increases as salinity increases, leading to decrease a sealing integrity i.e., threshold pressure of caprock including mudstone and/or shale. However, such mechanisms of scCO₂/water/rock interaction are now still being uncleared. Our objective of this study is to investigate an effect of salinity on threshold pressure of natural mudstone, which takes from Kazusa group of Boso peninsula in Japan, in CO₂/brine system in order to provide an insight for better understanding of mechanisms of CO₂/water (brine)/rock interaction at temperature of 40° and pore pressures of 10 MPa for both CO2 and brine (NaCl), ranging from 0 to 2 molal. Our results demonstrated that threshold pressure value is consist until 0.5 molal NaCl corresponding to density of sea water, but when the salinity exceeds, its value shows a significant drop. It is further indicated that based on comparison results with a modified Young-Laplace eq. using interfacial tension and contact angle values proposed by several researchers, predicted values of threshold pressure increase linearly with increasing salinity and deviate from our experimental data. Thus, model prediction suggests that variation of threshold pressure related to salinity could not be explained fully by changes in interfacial tension and contact angle values with salinity. The present results should point out that salinity in formation water has a significant impact on sealing integrity of mudstone under conditions of geological storage of CO₂.