Title: Numerical modeling of cold magmatic CO₂ flux measurements for the exploration of hidden geothermal systems

Abstract

The most accepted conceptual model to explain surface degassing of cold magmatic CO₂ in volcanic-geothermal systems involves the presence of a gas reservoir. Here, numerical simulations using the TOUGH2-ECO2N V2.0 package are performed to get quantitative insights into how cold CO₂ soil flux measurements are related to reservoir and fluid properties. While the modeling is based on flux data measured at a specific geothermal site, the Acoculco caldera (Mexico), some general insights have been gained. Both the CO₂ fluxes at the surface and the depth at which CO₂ exsolves are highly sensitive to the dissolved CO₂ content of the deep fluid. If CO₂ mainly exsolves above the reservoir within a fracture zone, the surface CO₂ fluxes are not sensitive to the reservoir size but depend on the CO₂ dissolved content and the rock permeability. For gas exsolution below the top of the reservoir, surface CO₂ fluxes also depend on the gas saturation of the deep fluid as well as the reservoir size. The absence of thermal anomalies at the surface is mainly a consequence of the low enthalpy of CO₂. The heat carried by CO₂ is efficiently cooled down by heat conduction and to a certain extent by isoenthalpic volumemore » expansion depending on the temperature gradient. Thermal anomalies occur at higher CO₂ fluxes (>37,000 g m^-2 d^-1) when the heat flux of the rising CO₂ is not balanced anymore. Lastly, specific results are obtained for the Acoculco area (reservoir depth, CO₂ dissolved content, and gas saturation state).« less

Authors:

Peiffer, Loïc ^[1]; Wanner, Christoph ^[2]; Pan, Lehua ^[3]

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+ Show Author Affiliations

1. Universidad Nacional Autónoma de México, Temixco (Mexico)
2. Univ. of Bern (Switzerland)
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Publication Date:

Fri Sep 11 00:00:00 EDT 2015

Research Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Fossil Energy (FE); Swiss Competence Center for Energy Research‐Supply of Energy (SCCER‐SOE); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Geothermal Technologies Office

OSTI Identifier:

1501370

Grant/Contract Number:  

AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research. Solid Earth

Additional Journal Information:

Journal Volume: 120; Journal Issue: 10; Journal ID: ISSN 2169-9313

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; TOUGH2; numerical modeling; CO2 degassing; Acoculco; geothermal; exploration