Differences in CO₂‐Water‐Rock Chemical Reactions among ‘Sweet Spot’ Reservoirs: Implications for Carbon Sequestration

Abstract

The Lucaogou Formation, located in the Jimsar Sag, Junggar Basin, NW China, has great potential for shale oil resources. In the process of CO2‐EOR (CO2 enhance oil recovery), mineral dissolution, precipitation and transformation, leading to the local corrosion or blockage of reservoirs, have a significant influence on recovery. In this study, a combination of high‐temperature and high‐pressure laboratory experiments and coupled temperature/fluid‐chemistry multi‐field numerical simulations are used to investigate CO2‐water‐rock reactions under various reservoir conditions in the upper and lower ‘sweet spots’, to reveal the mechanisms underlying CO2‐induced mineral dissolution, precipitation and transformation. In addition, we quantitatively calculated the evolution of porosity over geological timescales; compared and analyzed the variability of CO2 transformation in the reservoir under a variety of temperature, lithology and solution conditions; and identified the main factors controlling CO2‐water‐rock reactions, the types of mineral transformation occurring during long‐term CO2 sequestration and effective carbon sequestration minerals. The results demonstrate that the main minerals undergoing dissolution under the influence of supercritical CO2 are feldspars, while the main minerals undergoing precipitation include carbonate rock minerals, clay minerals and quartz. Feldspar minerals, especially the initially abundant plagioclase in the formation, directly affects total carbon sequestration, feldspar‐rich clastic rocks therefore having considerable sequestration potential.

Hydrogeochemical characteristics, driving factors, and health risk assessment of karst groundwater in Southwest Hubei Province, China

“…Gibbs diagrams can be used to disclose the composition and variation trend of chemical ions in groundwater and determine whether their sources are controlled by waterrock interactions, evaporation, or precipitation (Chu et al, 2023;Gao et al, 2023;Yang et al, 2023;Zhang, Diao, et al, 2021). According to the obtained results, the groundwater samples collected from the study area are located in the central part of the Gibbs diagrams (Figure 4), indicating that water-rock interaction was the major factor controlling the hydrochemical characteristics of the karst groundwater.…”

Geological and Engineering ‘Sweet Spots’ in the Permian Lucaogou Formation, Jimusar Sag, Junggar Basin

“…The two members are further subdivided into four sandbody units, P 2 l 2 1 , P 2 l 2 2 , P 2 l 1 1 and P 2 l 1 2 (Zhang et al, 2017). The lithologies mainly include siltstone or, occasionally, fine-grained sandstone, mudstone and dolostone (Wu et al, 2017;Zhang et al, 2019;Pang et al, 2022;Yang et al, 2023). Siltstone or fine-grained sandstone, as well as dolostones deposited in beach bar-lake or delta front environments, act as the reservoir rocks, while mudstones (shales), which were formed in semi-deep lacustrine to deep lake environments, act as the source rocks (Cao et al, 2017;Zhang et al, 2019;Lai et al, 2022a).…”