First Advisor

Robert B. Perkins

Term of Graduation

Fall 2019

Date of Publication


Document Type


Degree Name

Master of Science (M.S.) in Geology






Hydrogeology -- Oregon, Flood basalts -- Oregon, Groundwater -- Oregon -- Analysis, Groundwater temperature, Heat storage, Analytical geochemistry



Physical Description

1 online resource (xii, 116 pages)


Deep direct use thermal energy storage (TES) is a low carbon emission method of geothermal energy storage and supply for large-scale residential, commercial, and manufacturing heating and cooling. The process entails repeated cycles of hot- or cold-water injection, storage, and extraction from slow groundwater flow zones within the deeper layers of an aquifer system. Though a promising technology, TES cycles may increase mineral dissolution and precipitation reactions, particularly at elevated temperatures. The ensuing mass transfer can form scale in heat exchange systems and alter aquifer porosity and permeability, processes that can reduce the operational efficiency of a TES system.

Within the Portland Basin, the underutilized Columbia River Basalt Group (CRBG) confined aquifer system has the potential to support TES operations. The feasibility of using TES in the Portland Basin CRBG was evaluated from a hydrogeochemical perspective by ascertaining the range of native groundwater chemistries associated with the target zone, identifying pertinent CRBG mineralogy, and determining geochemical processes that can impact the aquifer or heat exchanger both experimentally and using geochemical reaction modeling.

Analysis of CRBG groundwaters in western Oregon revealed that CRBG groundwater chemistry is influenced by calcite precipitation and mixing with underlying saline waters. A series of batch reaction experiments quantified the changes in water chemistry resulting from increasing aquifer temperatures and revealed that water-rock reactions are surface controlled. Results also suggest Ca concentrations are primarily controlled by calcite precipitation and dissolution, while the concentrations of other major cations are controlled by a complex series of incongruent mineral reactions.

The impact of TES operation on aquifer porosity and permeability will ultimately depend on the composition of groundwater in the target zone, and on the nature and extent of available reactive surfaces in contact with injected waters. Equilibrium and kinetic transport reaction models were used to constrain the impacts of heating on the aquifer and heat exchanger using a variety of initial groundwater compositions, mineral assemblages, reactive surface areas, temperatures, and flow rates. Modeling results suggest that calcite, siderite, and smectite clays are significant secondary mineral phases. Most kinetic transport simulations indicate some loss of porosity near the injection point when injected waters are heated to 70°C. This loss is minimized, though not necessarily eliminated, when waters are only heated to ~50°C. Under the most optimistic modeled conditions (using a less evolved water type, ample reactive silicate surfaces, lower temperatures, and low to modest flow rates) a slight increase in porosity near the injection point may occur. Under the most pessimistic conditions (using a mature water that is saturated or oversaturated with respect to calcite, little to no reactive silicates as in calcite-lined fracture porosity, higher temperatures, and higher flow rates), a greater than 10% porosity loss may occur within one seasonal cycle. Modeling the recycling of waters between two reservoirs maintained at 70°C and 40°C suggests porosity loss in both reservoirs, but that some porosity may be recovered in the 70°C reservoir over multiple cycles. These findings have implications for use of the basalts as a storage site for drinking water and carbon sequestration, in addition to TES.

Persistent Identifier

703070_supp_33726F54-0C1C-11EA-943A-D50F95EF0FC5 (1).xlsx (119 kB)
Compiled groundwater chemistry, data tables

703070_supp_3E60A57A-0C1C-11EA-9531-DA0F95EF0FC5.pdf (223 kB)
Compiled groundwater chemistry, additional figures

703070_supp_821577_D5765EA2-0CD8-11EA-94A0-08964D662D30 (1).xlsx (79 kB)
Batch reaction experimental data, tables

703070_supp_EF6B509A-0C1C-11EA-986E-A51195EF0FC5.pdf (388 kB)
Batch reaction experimental data, XRD reports

703070_supp_00F9CCBA-0C1D-11EA-8DF3-AC1195EF0FC5.pdf (1674 kB)
Batch reaction experimental data, SEM images

703070_supp_17B5C602-0C1D-11EA-B31A-BD1195EF0FC5.pdf (137 kB)
Batch reaction experimental data, inverse modeling scripts

703070_supp_2E2AD936-0C1D-11EA-80CC-E71195EF0FC5.pdf (210 kB)
Geochemical reaction modeling scripts