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<p>To improve the reliability of gravity-based geothermal reservoir characterization, this study evaluates density parameterization strategies for constraining gravity modeling and inversion in the complex volcanic setting of the Los Humeros Geothermal Field (LHGF), Mexico. We integrate gravity data, a 3-D geological model, and petrophysical measurements to evaluate three density parameterizations in the starting models: (C1) mean bulk density, (C2) compaction-corrected saturated bulk density, and (C3) a multimodal density distribution derived from lithologic sub-volumes. Forward modeling results show a consistently poor fit on the order of several mGal between observed and computed gravity data across all three parameterizations, characterized by a persistent negative bias in the computed gravity and only limited improvement despite optimized initial densities. Inverse modeling that accounts for compaction effects and saturated-porosity densities significantly reduces the misfit between observed and computed gravity, generally to below 1 mGal. A detailed misfit analysis reveals that our initial density values consistently underestimated optimal densities by 60–130 kg/m³. The misfit shows no systematic variation with depth but seems to be linked to lithology. The low salinity of reservoir fluids (≤ 4 g/L) suggests that salinity effects are negligible. The multi-modal density approach (C3) does not improve the fit and introduced skewness, likely due to volumetric estimates of lithologies derived from limited available data for the individual units. Inversion tests with varying probabilities of density and geometry changes revealed that for the LHGF a 70:30 ratio produced the most optimal model, confirming the overall consistency of the initial 3-D geological model with observed gravity data. Smaller density variations in pre-caldera units suggest greater homogeneity, while fault zones likely contribute to localized heterogeneity in the underlying units. Our results do not distinguish between the conventional and superheated sectors of the LHGF, highlighting that gravity anomalies in this volcanic system primarily reflect the geological structure rather than thermal or fluid characteristics. Finally, our methodology provides a practical framework for quantifying uncertainty of 3-D geological models.</p>

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In-situ density and litho-constrained modeling of gravity data in the Los Humeros geothermal field, Mexico

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月3日

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  • Natalia Cornejo-Triviño,
  • M. Leandra,
  • Weydt,
  • Ingo Sass,
  • Eva Schill

摘要

To improve the reliability of gravity-based geothermal reservoir characterization, this study evaluates density parameterization strategies for constraining gravity modeling and inversion in the complex volcanic setting of the Los Humeros Geothermal Field (LHGF), Mexico. We integrate gravity data, a 3-D geological model, and petrophysical measurements to evaluate three density parameterizations in the starting models: (C1) mean bulk density, (C2) compaction-corrected saturated bulk density, and (C3) a multimodal density distribution derived from lithologic sub-volumes. Forward modeling results show a consistently poor fit on the order of several mGal between observed and computed gravity data across all three parameterizations, characterized by a persistent negative bias in the computed gravity and only limited improvement despite optimized initial densities. Inverse modeling that accounts for compaction effects and saturated-porosity densities significantly reduces the misfit between observed and computed gravity, generally to below 1 mGal. A detailed misfit analysis reveals that our initial density values consistently underestimated optimal densities by 60–130 kg/m³. The misfit shows no systematic variation with depth but seems to be linked to lithology. The low salinity of reservoir fluids (≤ 4 g/L) suggests that salinity effects are negligible. The multi-modal density approach (C3) does not improve the fit and introduced skewness, likely due to volumetric estimates of lithologies derived from limited available data for the individual units. Inversion tests with varying probabilities of density and geometry changes revealed that for the LHGF a 70:30 ratio produced the most optimal model, confirming the overall consistency of the initial 3-D geological model with observed gravity data. Smaller density variations in pre-caldera units suggest greater homogeneity, while fault zones likely contribute to localized heterogeneity in the underlying units. Our results do not distinguish between the conventional and superheated sectors of the LHGF, highlighting that gravity anomalies in this volcanic system primarily reflect the geological structure rather than thermal or fluid characteristics. Finally, our methodology provides a practical framework for quantifying uncertainty of 3-D geological models.