An approach to modeling coupled thermal-hydraulic-chemical processes in geothermal systems

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Abstract

Interactions between hydrothermal fluids and rock alter mineralogy, leading to the formation of secondary minerals and potentially significant physical and chemical property changes. Reactive transport simulations are essential for evaluating the coupled processes controlling the geochemical, thermal and hydrological evolution of geothermal systems. The objective of this preliminary investigation is to successfully replicate observations from a series of hydrothermal laboratory experiments [Morrow et al., 2001] using the code TOUGHREACT. The laboratory experiments carried out by Morrow et al. [2001] measure permeability reduction in fractured and intact Westerly granite due to high-temperature fluid flow through core samples. Initial permeability and temperature values used in our simulations reflect these experimental conditions and range from 6.13 × 10−20 to 1.5 × 10−17 m2 and 150 to 300 °C, respectively. The primary mineralogy of the model rock is plagioclase (40 vol.%), K-feldspar (20 vol.%), quartz (30 vol.%), and biotite (10 vol.%). The simulations are constrained by the requirement that permeability, relative mineral abundances, and fluid chemistry agree with experimental observations. In the models, the granite core samples are represented as one-dimensional reaction domains. We find that the mineral abundances, solute concentrations, and permeability evolutions predicted by the models are consistent with those observed in the experiments carried out by Morrow et al. [2001] only if the mineral reactive surface areas decrease with increasing clay mineral abundance. This modeling approach suggests the importance of explicitly incorporating changing mineral surface areas into reactive transport models.

Additional publication details

Publication type Conference Paper
Publication Subtype Conference Paper
Title An approach to modeling coupled thermal-hydraulic-chemical processes in geothermal systems
Year Published 2011
Language English
Publisher Stanford Geothermal Program
Publisher location Stanford, California
Contributing office(s) Earthquake Science Center
Description 14 p.
Larger Work Type Conference Paper
Larger Work Title Proceedings, thirty-sixth Workshop on Geothermal Reservoir Engineering
Conference Title Proceedings, thirty-sixth Workshop on Geothermal Reservoir Engineering
Conference Location Stanford, California
Conference Date January 31-February 2, 2011
Online Only (Y/N) N
Additional Online Files (Y/N) N