Geomechanical simulation of the stress tensor rotation caused by injection of cold water in a deep geothermal reservoir

    Jeanne, Pierre and Rutqvist, Jonny and Dobson, Patrick F. and Garcia, Julio and Walters, Mark and Hartline, Craig and Borgia, Andrea (2015) Geomechanical simulation of the stress tensor rotation caused by injection of cold water in a deep geothermal reservoir. Journal of Geophysical Research: Solid Earth, 120 (12). pp. 8422-8438. DOI: https://doi.org/10.1002/2015JB012414

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    Official URL: http://doi.org/10.1002/2015JB012414

    Abstract

    We present a three-dimensional thermohydromechanical numerical study of the evolution and distribution of the stress tensor within the northwest part of The Geysers geothermal reservoir (in California), including a detailed study of the region around one injection well from 2003 to 2012. Initially, after imposing a normal faulting stress regime, we calculated local changes in the stress regime around injection wells. Our results were compared with previously published studies in which the stress state was inferred from inverting the focal plane mechanism of seismic events. Our main finding is that changes in stress tensor orientation are caused by injection-induced progressive cooling of the reservoir, as well as by the seasonal variations in injection rate. Because of the gravity flow and cooling around a liquid zone formed by the injection, the vertical stress reduction is larger and propagates far below the injection well. At the same time, the horizontal stress increases, mostly because of stress redistribution below and above the cooling area. These two phenomena cause the rotation of the stress tensor and the appearance of a strike-slip regime above, inside, and below the cooling area. The cooling and the associated rotation of the stress regime can play a significant role in the observed long-term deepening of the microseismicity below active injection wells.

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    Item Type: Article
    Subjects: Methodology > Method and procesing > Stress field modeling
    Region > USA > California > Geysers
    Inducing technology > Geothermal energy production
    Project: SHEER project > THE GEYSERS: geothermal energy production