Quartz dissolution and silica deposition in hot-dry-rock geothermal systems
The kinetics of quartz dissolution control the produced fluid dissolved silica concentration in geothermal systems in which the downhole residence time is finite. The produced fluid of the Phase I, Run Segment 5 experimental Hot Dry Rock (HDR) geothermal system at Fenton Hill, NM, was undersaturated with respect to quartz in one pass through the reservoir, suggesting that the rate of granite dissolution governed the outlet dissolved silica concentration in this system. The literature data for the rate of quartz dissolution in water from 65 to 625/sup 0/C is correlated using an empirical rate law which is first order in quartz surface area and degree of undersaturation of the fluid. The Arrhenius plot (ln k vs T/sup -1/) is linear over eight orders of magnitude of the rate constant, verifying the validity of the proposed rate expression. Carefully performed quartz dissolution experiments in the present study duplicated the literature data and completed the data base in the temperature range from 150 to 250/sup 0/C. Identical experiments using crushed granite indicate that the rate of quartz dissolution in the presence of granite could be as much as 1 to 2 orders of magnitude faster than the rates observed in the pure quartz experiments. A temperature dependent HDR reservoir model incorporates the quartz dissolution rate law to simulate the dissolved silica behavior during the Fenton Hill Run Segment 5 experiment. For this low-permeability, fracture-dominated reservoir, the assumptions of one-dimensional plug flow through a vertically-inclined rectangular fracture and one-dimensional rock heat conduction perpendicular to the direction of flow are employed. These simplifications lead to an analytical solution for the temperature field in the reservoir.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 6629722
- Report Number(s):
- LA-9404-T; ON: DE83004997
- Resource Relation:
- Other Information: Thesis
- Country of Publication:
- United States
- Language:
- English
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Summary - Hot Dry Rock R&D Strategies and Applications
Related Subjects
HOT-DRY-ROCK SYSTEMS
GEOTHERMAL FLUIDS
QUARTZ
DISSOLUTION
SILICA
ABUNDANCE
DEPOSITION
CHEMICAL REACTION KINETICS
GEOLOGIC MODELS
CHALCOGENIDES
ENERGY SYSTEMS
FLUIDS
GEOTHERMAL SYSTEMS
KINETICS
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
REACTION KINETICS
SILICON COMPOUNDS
SILICON OXIDES
Geothermal Legacy
152001* - Geothermal Data & Theory- Properties of Aqueous Solutions