Geochemical Effects on Storage Gases and Reservoir Rock during Underground Hydrogen Storage: A Depleted North Sea Oil Reservoir Case Study

Abstract

In this work, geochemical modelling using PhreeqC was carried out to evaluate the effects of geochemical reactions on the performance of underground hydrogen storage (UHS). Equilibrium, exchange, and mineral reactions were considered in the model. Moreover, reaction kinetics were considered to evaluate the geochemical effect on underground hydrogen storage over an extended period of 30 years. The developed model was first validated against experimental data adopted from the published literature by comparing the modelling and literature values of H2 and CO2 solubility in water at varying conditions. Furthermore, the effects of pressure, temperature, salinity, and CO2% on the H2 and CO2 inventory and rock properties in a typical sandstone reservoir were evaluated over 30 years. Results show that H2 loss over 30 years is negligible (maximum 2%) through the studied range of conditions. The relative loss of CO2 is much more pronounced compared to H2 gas, with losses of up to 72%. Therefore, the role of CO2 as a cushion gas will be affected by the CO2 gas losses as time passes. Hence, remedial CO2 gas injections should be considered to maintain the reservoir pressure throughout the injection and withdrawal processes. Moreover, the relative volume of CO2 increases with the increase in temperature and decrease in pressure. Furthermore, the reservoir rock properties, porosity, and permeability, are affected by the underground hydrogen storage process and, more specifically, by the presence of CO2 gas. CO2 dissolves carbonate minerals inside the reservoir rock, causing an increase in the rock’s porosity and permeability. Consequently, the rock’s gas storage capacity and flow properties are enhanced.

Underground Gas Storage in Saline Aquifers: Geological Aspects

“…In the case of underground carbon dioxide storage, the impacts will be determined by the reactivity of the rock matrix with the gas dissolved in water to form acidic calcium carbonate. During underground hydrogen storage (UHS), geochemical interactions can occur that involve stored hydrogen, cushion gas, reservoir fluids, and minerals [64,65]. These reactions may result in the conversion of hydrogen to other gases (methane and hydrogen sulfide), which will result in the loss of stored hydrogen.…”

Advancements, Challenges, and Perspectives of Flue Gas Injection in Subsurface Formations: A Comprehensive Review

“…Furthermore, the heterogeneity of reservoir rock has a considerable effect on the efficiency of flue gas injection. CO 2 dissolves carbonate minerals in the porous media, causing an increase in the rock’s permeability …”

“…Also, Saeed et al 108 investigated the flue gas injection by geochemical modeling using PHREEQC. On the basis of the results, the relative volume of CO 2 accelerates with the temperature increase and pressure drop.…”

“…CO 2 dissolves carbonate minerals in the porous media, causing an increase in the rock's permeability. 108 So, PHREEQC plays a crucial role in understanding and optimizing the geochemical interactions between flue gases and geological formations in the context of EOR and geosequestration. Its ability to accurately model and simulate these interactions contributes to the development of sustainable and efficient energy practices in the oil and gas industry.…”

Hydrogen Storage in Porous Rocks: A Bibliometric Analysis of Research Trends

“…During underground hydrogen storage, geochemical interactions may occur that involve the stored hydrogen, cushion gas, reservoir fluids and minerals [27,53]. These reactions can convert hydrogen to other gases (methane and hydrogen sulphide), which results in a loss of stored hydrogen.…”