 |
| Titel |
An approach for modeling geothermal reservoir behavior using the reactive transport simulator TOUGHREACT |
| VerfasserIn |
Jennifer Palguta, Colin F. Williams, Steven E. Ingebritsen, Stephen H. Hickman, Eric Sonnenthal |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049151
|
|
|
|
|
|
| Zusammenfassung |
| It is well-known that interactions between hydrothermal fluids and rock alter the primary
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 reservoirs. However, the many assumptions required by reactive
transport models make the application of numerical methods to predicting reservoir behavior
challenging. Therefore, continued assessment of numerical codes and modeling
approaches is required. The objective of this preliminary investigation is to successfully
replicate the observations from a series of laboratory experiments (Morrow et al., JGR,
106, B12, pp. 30551-30560, 2001) using the code TOUGHREACT. The laboratory
experiments carried out by Morrow et al. (2001) measure permeability reduction in
pre-fractured and intact Westerly granite core samples due to high-temperature fluid
flow through the samples. Initial permeability and temperature values used in our
simulations reflect the experimental conditions and range from 6.1 Ã 10-20 to
1.5 Ã 10-17Â m2 and 150 to 300Â °C, respectively. The primary mineralogy of the model rock
is plagioclase (40Â vol.%), K-feldspar (20Â vol.%), quartz (30Â vol.%), and biotite
(10Â vol.%). All initial parameters were selected for consistency with the experimental
conditions and to facilitate comparison between the simulations and experiments. The
simulations are further constrained by the requirement that permeability, relative
mineral abundances, and fluid chemistry agree with experimental observations. A
one-dimensional model was chosen to simulate the experiments. There are possible
advantages to this approach. Because parameters given by Morrow et al. (2001) are
for the bulk media, this approach facilitates the use of their data in our models.
Additionally, an approach utilizing bulk-media parameters may prove useful for field
problems where fracture distributions or geometries are poorly known. We find that this
modeling approach correctly predicts the experimentally observed trends in fracture
permeability, solute composition, and mineral precipitation over time only if the mineral
reactive surface areas in the model decrease with increasing clay mineral abundance.
Importantly, we successfully simulate the observations from the various experiments
equally well using this approach. Our results indicate that to some extent geothermal
reservoir evolution can be adequately depicted using a relatively straightforward
formulation that explicitly considers the temporal evolution of reactive surface
areas. These results will be compared to more complex multi-dimensional models to
help identify the processes that dominate geothermal reservoir evolution. A better
understanding of coupled thermal-chemical-hydrologic phenomena will facilitate
future development of models that can be realistically applied to field problems. |
|
|
|
|
|
|