Alterations of geochemical properties of a tight sandstone reservoir caused by supercritical CO2-brine-rock interactions in CO2-EOR and geosequestration. (December 2018)

• Record Type: Journal Article
• Authors: Zhang, Xiang; Wei, Bing; Shang, Jing; Gao, Ke; Pu, Wanfen; Xu, Xingguang; Wood, Colin; Sun, Lin
• Is Part Of: Journal of CO₂ utilization. Volume 28(2018)
• Page Start: 408
• Page End: 418
• Publication Date: 2018-12
• Subjects: Tight reservoirs -- CO2-EOR -- CO2geosequestration -- Mineral dissolution -- Mineralogical changes -- Geochemical properties; Carbon dioxide -- Periodicals; Carbon dioxide -- Environmental aspects -- Periodicals; Carbon dioxide mitigation -- Periodicals; Carbon dioxide; Carbon dioxide -- Environmental aspects; Carbon dioxide mitigation; Periodicals; 628.53205
• DOI: 10.1016/j.jcou.2018.11.002
• Languages: English
• ISSNs: 2212-9820

Abstract

Highlights: Supercritical CO2 -EOR coupled with geosequestration were proposed in a Chinese tight oil reservoir. CO2 exposure experiments using real reservoirs core and brine were conducted under reservoir conditions. The alterations of geochemical properties of the tight reservoirs rock were elucidated. The changes of surface mineralogy, morphology, wettability, etc., were discussed. The underlying mechanisms for these alterations were clarified using integrative techniques. Abstract: The geochemistry of a reservoir is of great significance for CO2 Enhanced Oil Recovery (CO2 -EOR) and CO2 geosequestration operations. However, due to the massive diversity in mineralogy and physicochemistry of different reservoirs, the current data base is not yet sufficient to conclusively determine the alterations of geochemical prosperities when CO2 is injected especially for tight reservoirs. The attention of this work was given to a tight sandstone reservoir in Lucaogou formation of Jimsar sag (China). The interactions of reservoir rocks, formation brine and supercritical CO2 were extensively investigated under reservoir conditions (75 °C and 32 MPa) aiming to reveal possible mechanisms behind. The results showed that the dissolution of supercritical CO2 in the brine created an acidic environment (solubility = 0.94 mol/Kg), which induced the dissolution of minerals into the brine and their subsequent precipitation. The primary precipitants in this work were found to be iron minerals and kaolinite, as evidenced by Scanning Electron Microscopy and Energy Dispersion Spectrum (SEM-EDS) analyses. Moreover, the SEM-EDS observations have shown clear signs of mineralogical changes of the rocks with the preferred dissolution of K-feldspar, albite and ankerite. Kaolinitation due to the corrosion of K-feldspar and albite occurred during the CO2 -exposure experiments. The mineral surface after exposure to CO2 was altered to be more water-wet as a result of mineral dissolution, kaolinite formation and surface corrosion.