The Influence of Fluid Properties on Geometric Complexity and Breakdown Pressure of Hydraulic Fracture

Open Access
Author:
Alpern, Jennifer Staci
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 03, 2013
Committee Members:
  • Chris Marone, Thesis Advisor
Keywords:
  • hydraulic fracture
  • unconventional
  • hydrocarbon
  • geology
Abstract:
Hydraulic fracture has emerged as a powerful tool for enhancing extraction and recovery of hydrocarbons from conventional and unconventional geologic resources. We study the processes and conditions for the development of geometrically complex networks of hydraulic fracture under stresses appropriate for Earth’s shallow subsurface. We report on laboratory experiments designed to investigate the influence of fracture fluid and stress field on breakdown pressure and fracture complexity. Our experiments include unusually well-controlled conditions and we formulate new, efficient approaches that can be applied in future, field-scaled tests. Laboratory samples include Polymethyl methacrylate (PMMA), Pennsylvania Bluestone, and Green River Shale. Fracture fluids include water, argon, carbon dioxide, helium, nitrogen, and sulfur hexafluoride. Experiments were carried out at room temperature of ~25°C. Under the conditions of our study, the gases used are typically in a liquid or supercritical form when fracturing occurs. We find that supercritical fluids produce hydraulic fracture at significantly lower pressure than liquids, and that fracture complexity is significantly greater for supercritical fluids. These results can be explained by concepts related to capillary entry pressure within microcracks and differences in fluid access to crack tip regions as a function of fluid surface tension. Only supercritical fluids access the highest stress concentrations at crack tip regions. We propose a quantitative measure of fracture complexity and discuss the relationship between pore fluid properties, fracture network complexity, and sample fracture pressure. The majority of our work focused on PMMA. We report on initial data sets for Pennsylvania Bluestone and Green River Shale. This research provides new insights on the physicochemical processes that dictate hydraulic fracture.