Lead: Alexis Navarre-Sitchler
Goal: Develop a predictive micro- to core-scale understanding of the chemo-mechanical processes operative at the enhanced geothermal systems (EGS) testbed that impact permeability and their electrical and elastic-wave-scattering signatures.
The large-scale properties of EGS sites are fundamentally controlled by behaviors at a much smaller scale. This thrust focuses on developing a basic understanding of these micro- and core-scale chemo-mechanical phenomena.
Task 1.1: Defining EGS testbed-relevant geochemical equilibria and reaction kinetics
Developing a detailed understanding of mineral dissolution and precipitation rates during fluid flow through fractures in rock is central to CUSSP work. This task focuses on establishing a database of relevant aqueous equilibria and geochemical reaction kinetics for the rock type at the SURF testbed. This information will help define the conditions used in both laboratory-scale experiments and simulations. Initial work using a simple setup in PFLOTRAN showed that calcite dissolution and reprecipitation processes can lower the porosity in fractures, impacting fluid flow. A combination of literature data and laboratory experiments on rocks from the testbed will contribute to this important database.
Task 1.2: Understanding nanoscale reactive flow and the fundamental origins of electrical signals
Carbonate minerals like calcite are incredibly common across the world and have significant reactivity when water is present. Carbonate ions can dissolve and react with other metals, precipitating and changing the microscopic structure of underground fracture networks. The interfaces between the minerals and water represent an important site of reactivity and change. This task will focus on understanding how the surfaces of carbonate minerals respond, both chemically and physically, to testbed-relevant conditions. It will also focus on studying the electrical signatures of these changes. This work relies on the unique combination of analytical techniques and expertise available to the CUSSP team.
Task 1.3: Microscale reactive flow, fluid/mineral equilibria/kinetics, and signals
In EGS, the rock, fracture network, and fluids combine to form a dynamic environment. Understanding how the rock along fracture surfaces and fluid properties evolve at a microscopic level is important for developing an accurate picture of how fracture networks change over time. This task focuses on using advanced imaging techniques, both in situ and ex situ, as well as novel microscale geophysical measurements to observe both fluid and rock properties. The flow-based measurements will span from the single fracture to core scale and reactive transport studies will move from the molecular to fracture scale. This task is essential to connecting process information across EGS-relevant scales.
Task 1.4: Pore scale to core scale: Connecting reactive fracture flow and deformation to geophysical signals
This task will take the understanding of geochemical reactions and flow processes at the micro- and nanoscale developed in the other tasks from Thrust 1 and use it to identify how various reactions may combine to affect rock. By taking samples from the testbed, both pristine and following experiments, the team will determine how different processes affect the rock at a range of scales. The results from this task will directly feed into experimental design for Thrust 2.
