Ph.D. Thesis Defense Announcement

LABORATORY CHARACTERIZATION OF ROCKS AT HIGH TEMPERATURE USING INSTRUMENTED INDENTATION: IMPLICATIONS TO HYDROCARBON EXTRACTION AND GEOTHERMAL RECOVERY

by

Wilson Espinoza

Advisor(s):

Dr. Sheng Dai (CEE)

Committee Members:

Dr. Chloe Arson (CEE), Dr. J. David Frost (CEE), Dr. Zhigang Peng (EAS), Dr. Timothy Kneafsey (Lawrence Berkeley National Lab), Dr. Jean-Michel Pereira (ENPC, France)

Date & Time: June 30, 2021 9:00 AM

Location: (in-person) Sustainable Education Building (SEB-122), (virtual) https://bluejeans.com/821466063

The subsurface provides more than 80% of the energy nowadays in the U.S., and potentially billions of watts of electrical power from clean geothermal energy in the near future. Safe and efficient subsurface energy recovery requires a thorough understanding of deep subsurface geomaterials at in situ conditions. This research aims to understand the impacts of temperature on the fundamental properties of sedimentary and metamorphic crystalline rock, and to use the gained knowledge to understand reservoir response during fuel and geothermal energy extraction and to develop advanced formation treatment technologies for safe and efficient subsurface exploration.
We used instrumented nanoindentation to quantify the modulus, hardness, fracture toughness, and creep of shale, quartz, albite, biotite, and two granitic samples from geothermal reservoirs (i.e., SigmaV in South Dakota and FORGE in Utah) at temperatures up to 400⁰⁰C. We observed the brittle to ductile transition in tested Longmaxi shale with increased temperature, most likely due to thermally induced release of bonded water, microfracture closure, and fracture generation. We also observed such brittle to ductile transition in both monomineralic and polymineralic metamorphic rocks upon heating, and material degradation attributed to heterogeneous mineral expansion, and the competing effects between crack generation and crack healing upon heating evidenced through fracture initiation events and fracture toughness measurements. We established the linkage between the characteristic creep deformation and measured elastic modulus in tested monomineralic and polymineralic crystalline rocks.