Slip tendency analysis of fracture networks to determine suitability of candidate testbeds for the EGS collab hydroshear experiment

The EGS Collab Team Multiple affiliations

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Scopus citations

Abstract

Experiment 2 of the EGS Collab project is aimed at testing stimulation by hydro-shearing of existing natural fractures, versus Experiment 1, which is focused on hydraulic fracturing a rock mass to enhance permeability. The main criterion for the testbed selection in Experiment 2 is the presence of an interconnected network of fractures, at least 10 meters in extent, and with orientations such that shear slip can be induced at injection pressures less than the minimum horizontal stress (Shmin). The feasibility analysis for this experiment requires a well-constrained stress state along with well-characterized fracture networks. The fracture systems at two candidate locations in the Sanford Underground Research Facility (SURF), the 4850 Level (number refers to depth below ground surface in feet) and the 4100 Level, have been characterized to different extents. The 4850 Level has a well-characterized Discrete Fracture Network (DFN) from borehole (drilled for an experimental test bed) and drift observations. In contrast, the 4100 level has a fracture network characterized only by observations from the drift wall, which provides little constraint on fracture extents. This paper will present assessments for the interpreted slip potential for the natural fractures at the two locations. Data uncertainties are addressed by performing a probabilistic analysis that takes into account the uncertainty in the stress state, uncertainty in the fracture properties, and preliminary borehole locations. There is strong evidence of shear stimulation of some natural fractures in Experiment 1 on the 4850 level. We use examples of natural fractures strongly linked to shear stimulation in Experiment 1 from multiple monitoring indicators to test the consistency of the stress model and guide the uncertainty interpretation. This analysis is intended to guide the site selection process for Experiment 2 by highlighting the fracture orientations that are likely to be shear-stimulated in a majority of modeled realizations.

Original languageEnglish (US)
Title of host publicationGeothermal
Subtitle of host publicationGreen Energy for the Long Run - Geothermal Resources Council 2019 Annual Meeting, GRC 2019
PublisherGeothermal Resources Council
Pages405-424
Number of pages20
ISBN (Electronic)0934412243, 9781713806141
StatePublished - 2019
EventGeothermal Resources Council 2019 Annual Meeting - Geothermal: Green Energy for the Long Run, GRC 2019 - Palm Springs, United States
Duration: Sep 15 2019Sep 18 2019

Publication series

NameTransactions - Geothermal Resources Council
Volume43
ISSN (Print)0193-5933

Conference

ConferenceGeothermal Resources Council 2019 Annual Meeting - Geothermal: Green Energy for the Long Run, GRC 2019
CountryUnited States
CityPalm Springs
Period9/15/199/18/19

All Science Journal Classification (ASJC) codes

  • Renewable Energy, Sustainability and the Environment
  • Energy Engineering and Power Technology
  • Geophysics

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