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Title: Pore-scale supercritical CO 2 dissolution and mass transfer under drainage conditions

Abstract

Abstract: Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO 2 (scCO 2) and a prolonged depletion of residual scCO 2. In this study, pore-scale scCO 2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO 2 into the sandstone-analogue pore network initially saturated by water without dissolved CO 2 (dsCO 2). During the experiments, time-lapse images of dye intensity, reflecting water pH, were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO 2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO 2 dissolution and phase equilibrium occurs when scCO 2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore whenmore » a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO 2 dissolution at phase interfaces and diffusion of dsCO 2 at the pore scale (10-100 µm) observed after scCO 2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO 2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. This finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO 2 at narrow pore throats.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1344032
Report Number(s):
PNNL-SA-122892
Journal ID: ISSN 0309-1708; 49072; 48255; KP1704020
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Advances in Water Resources; Journal Volume: 100; Journal Issue: C
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; Environmental Molecular Sciences Laboratory

Citation Formats

Chang, Chun, Zhou, Quanlin, Oostrom, Mart, Kneafsey, Timothy J., and Mehta, Hardeep. Pore-scale supercritical CO2 dissolution and mass transfer under drainage conditions. United States: N. p., 2017. Web. doi:10.1016/j.advwatres.2016.12.003.
Chang, Chun, Zhou, Quanlin, Oostrom, Mart, Kneafsey, Timothy J., & Mehta, Hardeep. Pore-scale supercritical CO2 dissolution and mass transfer under drainage conditions. United States. doi:10.1016/j.advwatres.2016.12.003.
Chang, Chun, Zhou, Quanlin, Oostrom, Mart, Kneafsey, Timothy J., and Mehta, Hardeep. Wed . "Pore-scale supercritical CO2 dissolution and mass transfer under drainage conditions". United States. doi:10.1016/j.advwatres.2016.12.003.
@article{osti_1344032,
title = {Pore-scale supercritical CO2 dissolution and mass transfer under drainage conditions},
author = {Chang, Chun and Zhou, Quanlin and Oostrom, Mart and Kneafsey, Timothy J. and Mehta, Hardeep},
abstractNote = {Abstract: Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO2 (scCO2) and a prolonged depletion of residual scCO2. In this study, pore-scale scCO2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO2 into the sandstone-analogue pore network initially saturated by water without dissolved CO2 (dsCO2). During the experiments, time-lapse images of dye intensity, reflecting water pH, were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO2 dissolution and phase equilibrium occurs when scCO2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO2 dissolution at phase interfaces and diffusion of dsCO2 at the pore scale (10-100 µm) observed after scCO2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. This finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO2 at narrow pore throats.},
doi = {10.1016/j.advwatres.2016.12.003},
journal = {Advances in Water Resources},
number = C,
volume = 100,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}