Experimental Study on CO[sub.2] Geochemical Reaction Characteristics in Marine Weakly Consolidated Sandstone Saline Aquifers

• Published in: Processes Vol. 11; no. 12
• Main Authors: Xie, Mingying, Tu, Zhiyong, Sun, Xiaona, Yan, Zhenghe, Feng, Shasha, Zhang, Deng, Li, Fuyang, Zhang, Liang
• Format: Journal Article
• Language: English
• Published: MDPI AG 01.11.2023
• Subjects: Aquifers; Carbonate minerals; Carbonates; Gas fields; Permeability; South China Sea; United Kingdom
• ISSN: 2227-9717; 2227-9717
• DOI: 10.3390/pr11123345

Geological storage is one of the most important measures to reduce carbon emissions. The newly developed oilfield A in the Pearl River Mouth Basin of the South China Sea is associated with a large amount of CO[sub.2] with a purity of up to 95%. Two weakly consolidated sandstone saline aquifers located above the oil reservoir can be used for CO[sub.2] storage, but the CO[sub.2] geochemical reaction characteristics in the aquifers should be investigated clearly, which may cause significant damage to the physical properties of the reservoirs and caprocks of the aquifers. In this paper, static CO[sub.2] geochemical reaction experiments and rock thin section identifications were carried out using drill cuttings and sidewall cores, respectively. A numerical simulation was conducted according to the reactor conditions to explore the equilibrium state of the CO[sub.2] geochemical reaction. Through these studies, the characteristics of the geochemical reaction, its impact on the physical properties of the formation, and the CO[sub.2] storage potential by mineral trapping in the target aquifers were revealed. The results show that the two saline aquifers have similar physical properties. The reservoirs are mostly made up of fine-to-medium-grained sandstones as quartz arenite with a considerable amount of feldspar, which can provide favorable pore space for CO[sub.2] storage, while the caprocks are fine-grained felsic sedimentary rocks that can have a good sealing effect. However, both the reservoirs and caprocks contain a certain amount of carbonate and clay minerals. Mineral dissolution dominates in the CO[sub.2] geochemical reaction process, and more Ca[sup.2+] and Mg[sup.2+] is released into the formation water. The theoretical maximum CO[sub.2] mineral trapping capacity in the aquifers is 0.023–0.0538 mol/100 g rock, but due to the dynamic equilibrium of the geochemical reaction, the amount of mineralized CO[sub.2] in most of the rock samples is negative, and the average utilization factor is only −55.43%. As a result, the contribution of mineral trapping to the CO[sub.2] storage capacity takes −0.32%, which can be ignored. In the future, it is necessary to conduct detailed research to reveal the effect of a CO[sub.2] geochemical reaction on storage safety, especially in offshore weakly consolidated sandstone saline aquifers, which could be important sites for large-scale CO[sub.2] storage in China.