Influence of organic matter on CO2 and H2 wettability of petroleum reservoirs

Author Identifier

Mujahid Ali

Date of Award


Document Type

Thesis - ECU Access Only


Edith Cowan University

Degree Name

Doctor of Philosophy


School of Engineering

First Supervisor

Stefan Iglauer

Second Supervisor

Alireza Keshavarz

Third Supervisor

Muhammad Arif

Fourth Supervisor

Monica Sanchez


Carbon geo sequestration (CGS) is considered one of the promising approaches to reducing anthropogenic greenhouse gas emissions into the environment. Furthermore, Underground Hydrogen Storage (UHS) has been also identified as a viable solution to effectively stored hydrogen in geological formations. The underground storage of hydrogen (UHS) project has the potential to overcome the supply and demand imbalance by a subsequent withdrawal during periods of renewable energy shortage. Depleted petroleum reservoirs and deep saline aquifers are considered favorable candidates for long-term H2 and CO2 storage. H2 and CO2 become trapped in the reservoir by various physical and chemical mechanisms, and these mechanisms mainly include residual trapping and structural trapping, dissolution, and mineralization trapping. The wettability of rock minerals for storage gas in the presence of brine is a significant physicochemical factor that largely affects the trapping mechanism.

The reservoir formations naturally contain small concentrations of water-soluble organic components in particular humic acid (HA). These organic components in formations also assist the growth of various natural organotrophic microorganisms. While the earlier investigations suggest the impact of organic matter and microorganisms on wetting behaviour for enhanced oil recovery applications, we here argue that these organic matter and microorganisms have a significant effect on the CO2 and H2 wettability of the subsurface formations as well. Therefore, we prepared organic acid and bacteria-treated surfaces, and the effects of these treated surfaces on the H2 and CO2 wettability of subsurface reservoirs were evaluated via advancing and receding contact angle measurements, streaming zeta potential, and NMR techniques, at various organic acid concentrations, high pressures (up to 25 MPa), elevated temperatures (up to 333 K) and brine salinity (up to 0.3 M NaCl), that simulate the subsurface reservoir conditions. The surface characterizations were examined by high-resolution scanning electron microscopy (SEM) and atomic force (AFM) microscopy imaging while other characterization tools (e.g. TOC, EDX, and FTIR) were also implemented to gain a broader insight into the observed wetting behaviour.

Our results demonstrate that water-soluble organic acid concentration significantly changes rock wettability from water-wet (0-50o) towards CO2-wet (90-110o). Furthermore, a strong correlation exists between surface adsorption of organic acid and streaming potential coefficient, where the amount of residual water saturation decreases in organic acid aged cores – suggesting the presence of organic acid changes wettability towards CO2 wet in pores. The low organic content WA basalt was initially water-wet but with increasing pressure, it was also converted into a completely CO2-wet at pressures exceeding 15 MPa and 323 K. The results of bacteria-treated quartz surfaces suggest that (1) bacterial growth is prominent on the quartz surfaces with organic matter and, (2) the originally hydrophilic surfaces tend to become less hydrophilic while the hydrophobic surfaces turn less hydrophobic in the presence of microorganisms. The results of this investigation provide a fundamental understanding of H2 and CO2 wettability alteration in the subsurface microbial environment along with organic acid, thus, having implications for de-risk the large-scale carbon geo-sequestration (CGS) and underground hydrogen storage (UHS) projects.

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