Hydrothermal alteration is a common process in active geothermal systems and can significantly change the physiochemical properties of rocks. To improve reservoir assessment and modeling of high-temperature geothermal resources linked to active volcanic settings, a detailed understanding of the reservoir is needed. The Los Humeros Volcanic Complex, hosting the third largest exploited geothermal field in Mexico, represents a natural laboratory to investigate the impact of hydrothermal processes on the rock properties through andesitic reservoir cores and outcropping analogs. Complementary petrographic and chemical analyses were used to characterize the intensities and facies of hydrothermal alteration. The alteration varies from argillic and propylitic facies characterized by no significant changes of the REE budget indicating an inert behavior to silicic facies and skarn instead showing highly variable REE contents. Unaltered outcrop samples predominantly feature low matrix permeabilities (< 10–17 m2) as well as low to intermediate matrix porosities (< 5–15%), thermal conductivities (0.89–1.49 W m−1 K−1), thermal diffusivities (~ 0.83 10–6 m2 s−1), and sonic wave velocities (VP: ~ 2800–4100 m s−1, VS: ~ 1600–2400 m s−1). Average magnetic susceptibility and specific heat capacity range between 2.4–7.0 10–3 SI and 752–772 J kg−1 K−1, respectively. In contrast, the hydrothermally altered reservoir samples show enhanced porosities (~ 7–23%), permeabilities (10–17–10–14 m2), and thermal properties (> 1.67 W m−1 K−1; > 0.91 10–6 m2 s−1), but a significant loss of magnetic susceptibility (10–3–10–6 SI). In particular, this latter characteristic appears to be a suitable indicator during geophysical survey for the identification of hydrothermalized domains and possible pathways for fluids. The lack of clear trends between alteration facies, alteration intensity, and chemical indices in the studied samples is interpreted as the response to multiple and/or repeated hydrothermal events. Finally, the proposed integrated field-based approach shows the capability to unravel the complexity of geothermal reservoir rocks in active volcanic settings.

中文翻译：

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热液蚀变对储层岩石理化特征的影响：以Los Humeros地热田（墨西哥）为例

热液蚀变是活跃地热系统中的常见过程，可以显着改变岩石的物理化学性质。为了改进与活动火山环境相关的高温地热资源的储层评估和建模，需要对储层进行详细了解。Los Humeros 火山综合体是墨西哥第三大已开发地热田的所在地，是一个天然实验室，通过安山岩储层岩心和露头类似物研究热液过程对岩石特性的影响。互补的岩相学和化学分析用于表征热液蚀变的强度和相。变化从以 REE 预算没有显着变化为特征的泥质和青石相变化，表明惰性行为到硅质相和矽卡岩，而不是显示出高度可变的 REE 含量。未改变的露头样品主要具有低基质渗透率 (< 10–17 m2) 以及低至中等基质孔隙率 (< 5–15%)、热导率 (0.89–1.49 W m-1 K-1)、热扩散率 (~ 0.83 10–6 m2 s−1) 和声波速度 (VP: ~ 2800–4100 m s−1, VS: ~ 1600–2400 m s−1)。平均磁化率和比热容范围分别在 2.4-7.0 10-3 SI 和 752-772 J kg-1 K-1 之间。相比之下，热液蚀变的储层样品显示出增强的孔隙度 (~ 7–23%)、渗透率 (10–17–10–14 m2) 和热特性 (> 1.67 W m-1 K-1; > 0.91 10–6 m2 s−1), 但磁化率显着降低（10-3-10-6 SI）。特别是，后一种特征似乎是地球物理调查期间识别热液域和流体可能路径的合适指标。研究样品中蚀变相、蚀变强度和化学指标之间缺乏明确的趋势被解释为对多次和/或重复的热液事件的响应。最后，所提出的基于现场的综合方法显示了在活跃的火山环境中解开地热储层岩石复杂性的能力。后一种特征似乎是地球物理调查期间确定热液域和可能的流体路径的合适指标。研究样品中蚀变相、蚀变强度和化学指标之间缺乏明确的趋势被解释为对多次和/或重复的热液事件的响应。最后，所提出的基于现场的综合方法显示了在活跃的火山环境中解开地热储层岩石复杂性的能力。后一种特征似乎是地球物理调查期间确定热液域和可能的流体路径的合适指标。研究样品中蚀变相、蚀变强度和化学指标之间缺乏明确的趋势被解释为对多次和/或重复的热液事件的响应。最后，所提出的基于现场的综合方法显示了在活跃的火山环境中解开地热储层岩石复杂性的能力。