Pressure transient analysis during CO₂ push-pull tests into faults for EGS characterization

Journal Article · Sat May 26 00:00:00 EDT 2018 · Geothermics

DOI:https://doi.org/10.1016/j.geothermics.2018.05.004· OSTI ID:1477372

Jung, Yoojin ^[1]; Doughty, Christine ^[1]; Borgia, Andrea  ^[1]; Lee, Kyung Jae ^[2]; Oldenburg, Curtis M. ^[1]; Pan, Lehua ^[1]; Daley, Thomas M. ^[1]; Zhang, Rui ^[3]; Altundas, Bilgin ^[4]; Chugunov, Nikita ^[4]; Ramakrishnan, T. S. ^[4]

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1. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
2. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); University of Houston, TX (United States)
3. University of Louisiana, Lafayette, LA (United States)
4. Schlumberger-Doll Research, Cambridge, MA (United States)

Here, with the goal of detecting and characterizing faults and fractures in enhanced geothermal systems (EGS), a new technology involving CO₂ push-pull testing, active-source geophysical imaging, and well logging has recently been proposed. This technique takes advantage of (1) the contrasting properties of supercritical CO₂ and water which cause CO₂ to appear distinct from surrounding brine in seismic and other geophysical logging approaches, (2) the non-wetting nature of CO₂ which keeps it localized to the faults and fractures to create contrast potentially sufficient for active seismic and well-logging approaches to image faults and fracture zones at EGS sites. In this study, we evaluate the feasibility of using pressure transient monitoring during CO₂ push-pull tests to complement active seismic and wireline well logging for EGS characterization. For this purpose, we developed a 2D model of a prototypical geothermal site (Desert Peak, NV) that includes a single fault. The fault zone consists of a slip plane, fault gouge, and damage zone, and is bounded by the surrounding matrix of the country rock. Through numerical simulation using iTOUGH2, we found that the pressure transient at the monitoring wells in the fault gouge shows unique traits due to the multiphase flow conditions developed by CO₂ injection, and varies sensitively on the arrival of the CO₂ plume and the degree of CO₂ saturation. A sensitivity analysis shows the pressure transient is most sensitive to the fault gouge permeability, but also depends on multiphase flow parameters and the boundary conditions of the fault. Lastly, an inversion study reveals that the fault gouge permeability can be best estimated with the pressure transient data, whereas additional CO₂ saturation data do not improve the accuracy of the inversion significantly.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Geothermal Technologies Office; USDOE Office of Fossil Energy and Carbon Management (FECM)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1477372
• Alternate ID(s): OSTI ID: 1591666
• Journal Information: Geothermics, Vol. 75, Issue C; ISSN 0375-6505
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
enhanced geothermal sites (EGS)
CO2 push-pull
pressure transient
Desert Peak geothermal field
sensitivity analysis
parameter estimation
inverse modeling
iTOUGH2