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Title: Evaluation of Experimentally Measured and Model-Calculated pH for Rock-Brine-CO2 Systems under Geologic CO2 Sequestration Conditions

Abstract

Reliable pH estimation is essential for understanding the geochemical reactions that occur in rock-brine-CO2 systems when CO2 is injected into deep geologic formations for long-term storage. Due to a lack of reliable experimental methods, most laboratory studies of formation reactivities conducted under geologic CO2 sequestration (GCS) conditions have relied on thermodynamic modeling to estimate pH; however, the accuracy of these model predictions is typically uncertain. In this study, we expanded the measurement range of a spectrophotometric method for pH determination, and we applied the method to measure the pH in batch-reactor experiments utilizing rock samples from five ongoing GCS demonstration projects. A combination of color-changing pH indicators, bromophenol blue and bromocresol green, was shown to enable measurements over the pH range of 2.5-5.2. In-situ pH measurements were compared with pH values calculated using geochemical models. The effect of different thermodynamic databases on the accuracy of model prediction was evaluated. For rocks comprised of carbonate, siltstone, and sandstone, model results generally agreed well with experimentally measured pH; however, for basalt, significant differences were observed. These discrepancies may be due to the models’ failure to fully account for certain proton consuming and producing reactions that occur between the basalt minerals and CO2-saturatedmore » brine solutions.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1130710
Report Number(s):
PNNL-SA-95769
AA3030100
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Chemical Geology, 359:116-124
Additional Journal Information:
Journal Name: Chemical Geology, 359:116-124
Country of Publication:
United States
Language:
English
Subject:
CO2 sequestration, pH measurement, spectrophotometric

Citation Formats

Shao, Hongbo, Thompson, Christopher J., and Cantrell, Kirk J. Evaluation of Experimentally Measured and Model-Calculated pH for Rock-Brine-CO2 Systems under Geologic CO2 Sequestration Conditions. United States: N. p., 2013. Web. doi:10.1016/j.chemgeo.2013.09.021.
Shao, Hongbo, Thompson, Christopher J., & Cantrell, Kirk J. Evaluation of Experimentally Measured and Model-Calculated pH for Rock-Brine-CO2 Systems under Geologic CO2 Sequestration Conditions. United States. https://doi.org/10.1016/j.chemgeo.2013.09.021
Shao, Hongbo, Thompson, Christopher J., and Cantrell, Kirk J. 2013. "Evaluation of Experimentally Measured and Model-Calculated pH for Rock-Brine-CO2 Systems under Geologic CO2 Sequestration Conditions". United States. https://doi.org/10.1016/j.chemgeo.2013.09.021.
@article{osti_1130710,
title = {Evaluation of Experimentally Measured and Model-Calculated pH for Rock-Brine-CO2 Systems under Geologic CO2 Sequestration Conditions},
author = {Shao, Hongbo and Thompson, Christopher J. and Cantrell, Kirk J.},
abstractNote = {Reliable pH estimation is essential for understanding the geochemical reactions that occur in rock-brine-CO2 systems when CO2 is injected into deep geologic formations for long-term storage. Due to a lack of reliable experimental methods, most laboratory studies of formation reactivities conducted under geologic CO2 sequestration (GCS) conditions have relied on thermodynamic modeling to estimate pH; however, the accuracy of these model predictions is typically uncertain. In this study, we expanded the measurement range of a spectrophotometric method for pH determination, and we applied the method to measure the pH in batch-reactor experiments utilizing rock samples from five ongoing GCS demonstration projects. A combination of color-changing pH indicators, bromophenol blue and bromocresol green, was shown to enable measurements over the pH range of 2.5-5.2. In-situ pH measurements were compared with pH values calculated using geochemical models. The effect of different thermodynamic databases on the accuracy of model prediction was evaluated. For rocks comprised of carbonate, siltstone, and sandstone, model results generally agreed well with experimentally measured pH; however, for basalt, significant differences were observed. These discrepancies may be due to the models’ failure to fully account for certain proton consuming and producing reactions that occur between the basalt minerals and CO2-saturated brine solutions.},
doi = {10.1016/j.chemgeo.2013.09.021},
url = {https://www.osti.gov/biblio/1130710}, journal = {Chemical Geology, 359:116-124},
number = ,
volume = ,
place = {United States},
year = {Thu Nov 14 00:00:00 EST 2013},
month = {Thu Nov 14 00:00:00 EST 2013}
}