Burnside, N. , Westaway, R., Banks, D. , Zimmermann, G., Hofmann, H. and Boyce, A. J. (2019) Rapid water-rock interactions evidenced by hydrochemical evolution of flowback fluid during hydraulic stimulation of a deep geothermal borehole in granodiorite: Pohang, Korea. Applied Geochemistry, 111, 104445. (doi: 10.1016/j.apgeochem.2019.104445)
|
Text
200894.pdf - Published Version Available under License Creative Commons Attribution Non-commercial No Derivatives. 4MB |
Abstract
Flowback water from the 4215 m deep (True Vertical Depth) PX-1 borehole, following the August 2017 hydraulic stimulation of a granodiorite geothermal reservoir in Pohang, South Korea, was monitored for a suite of physicochemical, chemical and isotopic parameters. The results provide unique insights into mixing processes, fluid evolution and rapid water-rock interaction in a deep geothermal system. Injected water for stimulation was relatively fresh, oxidising surface water, with temperature 29.5 °C and pH c. 6.5. The flowback water showed an increasing content of most solutes, with the evolution conforming to an exponential ‘flushing’ model for conservative solutes such as chloride. Flowback water became progressively Na–Cl dominated, with a circumneutral pH (7.1) and negative oxidation-reduction potential (c. −180 mV). Some solutes (including, Na, K and Si) increased more rapidly than a flushing model would suggest, implying that these had been acquired by the flowback water due to mineral hydrolysis. Stable isotopes of O and H indicate that initially meteoric waters have undergone geothermal oxygen isotope exchange with minerals. Evolution of redox species in recovered water suggests progressively oxidising zonation around the injection borehole in an otherwise reducing reservoir. Rapidly increasing silica concentrations in flowback water suggests extensive quartz dissolution and indicated a reservoir temperature of up to 169 °C. This lends plausible, if equivocal support to the hypothesis that quartz dissolution by injection water may have contributed to triggering movement on the pre-stressed fault associated with the November 2017 Mw 5.5 Pohang earthquake.
| Item Type: | Articles |
|---|---|
| Additional Information: | This work was funded by the European Commission Horizon 2020 LCE ‘DESTRESS’ project (EC-691728). AJB was funded by, and isotopic analyses carried out at, the ICSF at SUERC (NERC Facility contract F14/G6/11/01). |
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Boyce, Professor Adrian and Burnside, Dr Neil and Banks, Mr David and Westaway, Dr Robert |
| Authors: | Burnside, N., Westaway, R., Banks, D., Zimmermann, G., Hofmann, H., and Boyce, A. J. |
| College/School: | College of Science and Engineering > School of Engineering > Systems Power and Energy College of Science and Engineering > Scottish Universities Environmental Research Centre |
| Journal Name: | Applied Geochemistry |
| Publisher: | Elsevier |
| ISSN: | 0883-2927 |
| ISSN (Online): | 1872-9134 |
| Published Online: | 18 October 2019 |
| Copyright Holders: | Copyright © 2019 The Authors |
| First Published: | First published in Applied Geochemistry 111:104445 |
| Publisher Policy: | Reproduced under a Creative Commons license |
University Staff: Request a correction | Enlighten Editors: Update this record
Deposit and Record Details
Deposit and Record Details