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Title: Simulations of CO2 injection into fractures and faults for improving their geophysical characterization at EGS sites

Journal Article · · Geothermics
 [1];  [1];  [2];  [1];  [1];  [1];  [3]
  1. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
  2. University of Louisiana, Lafayette, LA (United States)
  3. Schlumberger-Doll Research, Cambridge, MA (United States)
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Here, we propose the use of CO2 in push-pull well tests to improve geophysical identification and characterization of fractures and faults at enhanced geothermal system (EGS) sites. Using TOUGH2/ECO2N, we carried out numerical experiments of push-pull injection-production cycling of CO2 into idealized vertical fractures and faults to produce pressure-saturation-temperature conditions that can be analyzed for their geophysical response. Our results show that there is a strong difference between injection and production mainly because of CO2 buoyancy. While the CO2-plume grows laterally and upward during injection, not all CO2 is recovered during the subsequent production phase. Even under the best conditions for recovery, at least 10% of the volume of the pores still remains filled with CO2. To improve EGS characterization, comparisons can be made of active seismic methods carried out before and after (time lapse mode) CO2 injection into the fracture or fault. Here we find that across the CO2 saturation range, C11 (the normal stiffness in the horizontal direction perpendicular to the fracture plane) varies between maximum and minimum values by about 15%. It reaches a maximum at around 6% gas saturation, decreasing exponentially to a minimum at higher saturations. Finally, our results suggest that CO2 injection can be effectively used to infiltrate fault and fracture zones reaching about optimal saturation values in order to enhance seismic imaging at EGS sites.

Research Organization:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Organization:
USDOE Office of Fossil Energy (FE); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Geothermal Technologies Office; Environmental Design Research Association (EDRA)
Grant/Contract Number:
AC02-05CH11231
OSTI ID:
1476533
Alternate ID(s):
OSTI ID: 1550069
Journal Information:
Geothermics, Vol. 69, Issue C; ISSN 0375-6505
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 14 works
Citation information provided by
Web of Science

References (8)

Seismic properties of pore fluids journal November 1992
Numerical simulation of salt precipitation in the fractures of a CO2-enhanced geothermal system journal October 2012
Simulation of CO2-EGS in a Fractured Reservoir with Salt Precipitation journal January 2013
Contribution of the exploration of deep crystalline fractured reservoir of Soultz to the knowledge of enhanced geothermal systems (EGS) journal July 2010
Propagation pathways and fluid transport of hydrofractures in jointed and layered rocks in geothermal fields journal August 2002
Poroelastic modeling of seismic boundary conditions across a fracture journal August 2007
Experimental study on CO2 monitoring and quantification of stored CO2 in saline formations using resistivity measurements journal March 2010
A Closed-form Equation for Predicting the Hydraulic Conductivity of Unsaturated Soils1 journal January 1980

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Related Subjects

58 GEOSCIENCES
CO2 injection
faults characterization
faults imaging
S=seismic imaging
EGS