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Title: Numerical modeling of injection, stress and permeability enhancement during shear stimulation at the Desert Peak Enhanced Geothermal System

Abstract

Creation of an Enhanced Geothermal System relies on stimulation of fracture permeability through self-propping shear failure that creates a complex fracture network with high surface area for efficient heat transfer. In 2010, shear stimulation was carried out in well 27-15 at Desert Peak geothermal field, Nevada, by injecting cold water at pressure less than the minimum principal stress. An order-of-magnitude improvement in well injectivity was recorded. In this work, we describe a numerical model that accounts for injection-induced stress changes and permeability enhancement during this stimulation. We use the coupled thermo-hydrological–mechanical simulator FEHM to (i) construct a wellbore model for non-steady bottom-hole temperature and pressure conditions during the injection, and (ii) apply these pressures and temperatures as a source term in a numerical model of the stimulation. A Mohr–Coulomb failure criterion and empirical fracture permeability is developed to describe permeability evolution of the fractured rock. The numerical model is calibrated using laboratory measurements of material properties on representative core samples and wellhead records of injection pressure and mass flow during the shear stimulation. The model captures both the absence of stimulation at low wellhead pressure (WHP ≤1.7 and ≤2.4 MPa) as well as the timing and magnitude of injectivity risemore » at medium WHP (3.1 MPa). Results indicate that thermoelastic effects near the wellbore and the associated non-local stresses further from the well combine to propagate a failure front away from the injection well. Elevated WHP promotes failure, increases the injection rate, and cools the wellbore; however, as the overpressure drops off with distance, thermal and non-local stresses play an ongoing role in promoting shear failure at increasing distance from the well.« less

Authors:
ORCiD logo [1];  [2];  [3];  [4];  [5]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Stanford Univ., CA (United States). Dept. of Geophysics
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Temple Univ., Philadelphia, PA (United States)
  4. U.S. Geological Survey, Menlo Park, CA (United States)
  5. Baker Hughes Inc., Palo Alto, CA (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Geothermal Technologies Office (EE-4G)
OSTI Identifier:
1468563
Report Number(s):
LA-UR-14-27904
Journal ID: ISSN 1365-1609
Grant/Contract Number:  
AC52-06NA25396
Resource Type:
Accepted Manuscript
Journal Name:
International Journal of Rock Mechanics and Mining Sciences
Additional Journal Information:
Journal Volume: 78; Journal Issue: C; Journal ID: ISSN 1365-1609
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 15 GEOTHERMAL ENERGY; Desert Peak; Shear stimulation; Permeability enhancement; Thermal stress; Modeling

Citation Formats

Dempsey, David, Kelkar, Sharad, Davatzes, Nicholas, Hickman, Stephen, and Moos, Daniel. Numerical modeling of injection, stress and permeability enhancement during shear stimulation at the Desert Peak Enhanced Geothermal System. United States: N. p., 2015. Web. doi:10.1016/j.ijrmms.2015.06.003.
Dempsey, David, Kelkar, Sharad, Davatzes, Nicholas, Hickman, Stephen, & Moos, Daniel. Numerical modeling of injection, stress and permeability enhancement during shear stimulation at the Desert Peak Enhanced Geothermal System. United States. doi:10.1016/j.ijrmms.2015.06.003.
Dempsey, David, Kelkar, Sharad, Davatzes, Nicholas, Hickman, Stephen, and Moos, Daniel. Thu . "Numerical modeling of injection, stress and permeability enhancement during shear stimulation at the Desert Peak Enhanced Geothermal System". United States. doi:10.1016/j.ijrmms.2015.06.003. https://www.osti.gov/servlets/purl/1468563.
@article{osti_1468563,
title = {Numerical modeling of injection, stress and permeability enhancement during shear stimulation at the Desert Peak Enhanced Geothermal System},
author = {Dempsey, David and Kelkar, Sharad and Davatzes, Nicholas and Hickman, Stephen and Moos, Daniel},
abstractNote = {Creation of an Enhanced Geothermal System relies on stimulation of fracture permeability through self-propping shear failure that creates a complex fracture network with high surface area for efficient heat transfer. In 2010, shear stimulation was carried out in well 27-15 at Desert Peak geothermal field, Nevada, by injecting cold water at pressure less than the minimum principal stress. An order-of-magnitude improvement in well injectivity was recorded. In this work, we describe a numerical model that accounts for injection-induced stress changes and permeability enhancement during this stimulation. We use the coupled thermo-hydrological–mechanical simulator FEHM to (i) construct a wellbore model for non-steady bottom-hole temperature and pressure conditions during the injection, and (ii) apply these pressures and temperatures as a source term in a numerical model of the stimulation. A Mohr–Coulomb failure criterion and empirical fracture permeability is developed to describe permeability evolution of the fractured rock. The numerical model is calibrated using laboratory measurements of material properties on representative core samples and wellhead records of injection pressure and mass flow during the shear stimulation. The model captures both the absence of stimulation at low wellhead pressure (WHP ≤1.7 and ≤2.4 MPa) as well as the timing and magnitude of injectivity rise at medium WHP (3.1 MPa). Results indicate that thermoelastic effects near the wellbore and the associated non-local stresses further from the well combine to propagate a failure front away from the injection well. Elevated WHP promotes failure, increases the injection rate, and cools the wellbore; however, as the overpressure drops off with distance, thermal and non-local stresses play an ongoing role in promoting shear failure at increasing distance from the well.},
doi = {10.1016/j.ijrmms.2015.06.003},
journal = {International Journal of Rock Mechanics and Mining Sciences},
number = C,
volume = 78,
place = {United States},
year = {2015},
month = {7}
}

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