Fractures in Subsurface Energy Applications: Coupling Geochemical and Geomechanical Processes

Abstract

Many engineering applications utilize the subsurface to store fluids, examples

include carbon capture and sequestration, hydraulic fracturing, geothermal energy, and

deep well disposal. A major risk of utilizing the subsurface are rock fractures that could

allow for unwanted upward fluid migration or seismic activity. In this dissertation, I

advance the understanding of how coupled geochemical and geomechanical processes

affect the risks of leakage and seismicity of fractures, and present a novel geophyiscal

signal of geochemical alteration that could be used for monitoring the degradation of

fractures.

In Chapter 2, reactive-transport modeling is used to demonstrate that the spatial

pattern of less reactive mineral, not abundance, controls transmissivity evolution of rock

fractures in heterogenous calcite-rich shales subject to reactive flow. Results show a

banded mineral pattern creates persistent bottlenecks, prevents channelization, and

stabilizes transmissivity. As a consequence, banded mineral variation may limit reactive

evolution of fracture transmissivity and increase storage reliability.

In Chapter 3, I present a novel two-stage experimental method with flow and

mechanical shear to demonstrate that coupled geochemical and geomechanical processes

could favorably seal fractures but also increase the likelihood of induced seismicity.

During flow of acidic brine in laboratory experiments, reactive minerals selectively

dissolved and created a porous layer. This layer collapsed under normal stress, filling the

fracture with fine particles and decreasing permeability. However, in the laboratory

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experiments it was also observed that the frictional strength was reduced presumably

because the layer of fine particles prevented the formation of interlocking microasperities.

In Chapter 4, I use experimental methods to identify and demonstrate a novel

seismic wave transmission method to detect signatures of chemical alteration of fracture

surfaces. The porous layer that is created from selective mineral dissolution decreases the

fracture specific stiffness, slowing the wave velocity, and lowering the maximum wave

amplitude.

Lastly, in Chapter 5 I broaden the scope of my dissertation and build a bioenergy

with carbon capture and sequestration (BECCS) deployment optimization model across

the continental United States. This model is used to showcase that the potential future

negative emissions potential of BECCS is highly sensitive to the underlying biomass

supply.