Geomechanics of Unconventional Reservoirs: Hydraulic Fracturing and Nanoindentation

Abstract

Geomechanics is the study of the mechanical response of geologic formations subjected to injection, production, and storage of fluids in the subsurface. It plays a role in understanding formation integrity and the response to oil and gas depletion during well completion. Recent studies also relate geomechanics to energy transition methods, such as carbon capture storage and geothermal energy. In this thesis, we combine nanoindentation with hydraulic fracturing testing and acoustic emissions monitoring to approach one question. Can we combine nanoindentation and hydraulic fracturing laboratory testing to understand and improve solutions for common problematics in completions design, such as the reduction in hydraulic fracturing breakdown pressure, total stimulated reservoir volume, time-dependent deformation, and rock and fluid interactions? Using cyclic injection, a greater number of cycles reduced the monotonic breakdown pressure and the average seismic moment of induced acoustic events. The number of acoustic events increased with more cycles, reflected in a greater estimated stimulated reservoir volume (SRV). The 4-cycle test was the most efficient test, with the greatest SRV generated based on the work inputted. Additionally, nanoindentation showed linear gel as a damaging agent for carbonate-rich samples, ash beds to record a significantly lower Young’s modulus than the formation matrix, and modeled primary and secondary creep in shales, showing a dependency on clay and total organic content.