Effect of humic acid on CO2-wettability in sandstone formation

Mujahid Ali*, Faisal Ur Rahman Awan, Muhammad Ali, Ahmed Al-Yaseri, Muhammad Arif, Mónica Sánchez-Román, Alireza Keshavarz, Stefan Iglauer

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

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Hypothesis: Millions of tons of CO2 are stored in CO2 geological storage (CGS) formations (depleted oil reservoirs and deep saline aquifers) every year. These CGS formations naturally contain small concentrations of water-soluble organic components in particular humic acid (HA), which may drastically affect the rock wettability - a significant factor determining storage capacities and containment security. Hence, it is essential to characterise the effect of humic acid concentration on CO2-wettability and its associated impact on storage capacity. Experimental: To achieve this, we measured advancing and receding contact angles at reservoir conditions using the pendant drop tilted plate method for various humic acid concentrations (1, 10, and 100 mg/L) as a function of pressure (0.1–25 MPa), temperature (303–333 K), and brine salinity (0–0.3 M NaCl). Further, the influence of humic acid adsorption on the mineral's surface was examined by several independent techniques. Results: Our results demonstrate that humic acid significantly changes rock wettability from water-wet (0–50°) towards CO2-wet (90–110°). An increase in pressure, temperature, and salinity had a similar effect. Humic acid adsorption also increased the surface roughness of the substrates. We conclude that even trace amounts of humic acid (i.e. 1 mg/L), which exist in storage aquifers, significantly increase CO2-wettability and thus reduce structural and residual trapping capacities. Therefore, it is pertinent to account for these humic acid concentrations to de-risk CGS projects.

Original languageEnglish
Pages (from-to)315-325
Number of pages11
JournalJournal of Colloid and Interface Science
Early online date21 Dec 2020
Publication statusPublished - 15 Apr 2021


  • CO Storage
  • EOR
  • Humic Acid
  • Organic Acids
  • Trapping Capacities
  • Wettability


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