Date of Award

Spring 6-21-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Harihar Rajaram

Second Advisor

Satish Karra

Third Advisor

Roseanna M. Neupauer

Fourth Advisor

Richard A. Regueiro

Fifth Advisor

Anne F. Sheehan

Abstract

Unconventional oil and gas development is made economically feasible by horizontal drilling and hydraulic fracturing, and it can produce large volumes of wastewater that are injected into disposal wells. In the first part of this dissertation, we investigate the potential for fracturing fluid to migrate from the target formation to contaminate shallow drinking water aquifers. We present semianalytical calculations for capillary imbibition into shale, which can sequester up to 95% of the fracturing fluid, thus preventing migration to aquifers. Next, we present a numerical model of fracturing fluid migration, which is the first to combine injection and production, imbibition, and buoyancy. In the absence of a permeable pathway between the injection formation and the aquifer, no contamination occurs. In the presence of a permeable pathway, well suction and capillary imbibition significantly reduce the amount of fracturing fluid reaching the aquifer compared to scenarios that do not account for suction and imbibition. In part two, we present a new framework for modeling basin-scale injection-induced seismicity (IIS). The framework incorporates flow and geomechanics, the presence of fractures and faults, and the capability for hydraulic diffusivity to evolve with effective stress and earthquake history, which is modeled by the Mohr-Coulomb failure criteria. The model is implemented in the massively-parallel code PFLOTRAN, which is important to capture the large length scales (~10 km) and many fractures and faults (100-1000s). Applications of this model: (a) put constrains on the hydraulic diffusivity in basement rock, which may have been too large in previous modeling studies; (b) explain the heterogeneity of earthquake locations; and (c) capture the variations in critical pressure that cause earthquakes, based on stress state and fault orientation. In part three, we show work that verifies and increases the accuracy of subsurface simulators, which is important for the continued investigation of fluid migration, IIS, and other subsurface phenomena. First, we derive a porosity-pressure relationship for general subsurface flow codes (GSFs) which accounts for the relative velocity between pore fluid and rock matrix. Simulations using this relationship show excellent agreement between GSFs and the groundwater flow equation. Next we verify the fully-coupled flow and geomechanics implementation in PFLOTRAN by comparing to an analytical solution.

Available for download on Thursday, January 27, 2022

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