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Geochemical modeling of acid fluids in Los Humeros Geothermal Field

Bienkowski, R. and Torres Alvarado, I. S. and Hinderer, Matthias (2005):
Geochemical modeling of acid fluids in Los Humeros Geothermal Field.
In: Proceedings World Geothermal Congress 2005, Antalya, Turkey, 24-29 April 2005, [Article]

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Abstract

Los Humeros, located in the East of the Mexican central highland, is the third most important geothermal field in the country. In the past decade its electricity production has been affected by the occurrence of acid fluids. In this work, we present different geochemical models to shed some light upon the question of the origin of those fluids. Geologically, Los Humeros is emplaced within a Quaternary caldera, 24 km in diameter, which is built of acidic to intermediary lavas, tuffs and volcanic ashes, upon a sedimentary-metamorphic basement with subordinated intrusive rocks. The geothermal system apparently consists of two reservoirs. The upper reservoir is located at depths between 1025 m and 1600 m a. s. l., it is fluid-dominated and it shows measured temperatures up to 300°C. The lower reservoir (between 850 m and 100 m a. s. l.) can reach temperatures up to 400°C and is steam-dominated. Geochemical models were calculated using the software package SOLVEQ/CHILLER, due to its applicability for studying multiphase systems as well as boiling and mixing processes. Setting up a useful concept of acid development by means of the existing data was problematic. Our main difficulties were incomplete chemical analyses, the presence of fluids with enthalpy excess, as well as the lack of geological and geochemical data to distinct the lower from the upper aquifer. Principally, our models are based on the more complete data set existing for well H-1. The first model explores the possibility of the acid fluids arriving to the reservoirs from a yet unknown deposit, probably a deeper magma chamber underneath the reservoirs. Our calculations show that a contribution of 0.009 moles of HCl and 0.005 moles of HF would be enough to reach pH values as low as 3.5. Alternatively, a second model was calculated in which the geothermal fluid from Los Humeros has reacted with the corresponding aquifer rocks of the lower reservoir, in order to explore whether mineral reactions are responsible for the presence of acid fluids. According to our computations this hypothesis could hardly be responsible for the low pH values observed in the field.

Item Type: Article
Erschienen: 2005
Creators: Bienkowski, R. and Torres Alvarado, I. S. and Hinderer, Matthias
Title: Geochemical modeling of acid fluids in Los Humeros Geothermal Field
Language: English
Abstract:

Los Humeros, located in the East of the Mexican central highland, is the third most important geothermal field in the country. In the past decade its electricity production has been affected by the occurrence of acid fluids. In this work, we present different geochemical models to shed some light upon the question of the origin of those fluids. Geologically, Los Humeros is emplaced within a Quaternary caldera, 24 km in diameter, which is built of acidic to intermediary lavas, tuffs and volcanic ashes, upon a sedimentary-metamorphic basement with subordinated intrusive rocks. The geothermal system apparently consists of two reservoirs. The upper reservoir is located at depths between 1025 m and 1600 m a. s. l., it is fluid-dominated and it shows measured temperatures up to 300°C. The lower reservoir (between 850 m and 100 m a. s. l.) can reach temperatures up to 400°C and is steam-dominated. Geochemical models were calculated using the software package SOLVEQ/CHILLER, due to its applicability for studying multiphase systems as well as boiling and mixing processes. Setting up a useful concept of acid development by means of the existing data was problematic. Our main difficulties were incomplete chemical analyses, the presence of fluids with enthalpy excess, as well as the lack of geological and geochemical data to distinct the lower from the upper aquifer. Principally, our models are based on the more complete data set existing for well H-1. The first model explores the possibility of the acid fluids arriving to the reservoirs from a yet unknown deposit, probably a deeper magma chamber underneath the reservoirs. Our calculations show that a contribution of 0.009 moles of HCl and 0.005 moles of HF would be enough to reach pH values as low as 3.5. Alternatively, a second model was calculated in which the geothermal fluid from Los Humeros has reacted with the corresponding aquifer rocks of the lower reservoir, in order to explore whether mineral reactions are responsible for the presence of acid fluids. According to our computations this hypothesis could hardly be responsible for the low pH values observed in the field.

Journal or Publication Title: Proceedings World Geothermal Congress 2005, Antalya, Turkey, 24-29 April 2005
Series Name: World Geothermal Congress-2005 <Antalya/Türkei,2005>
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Earth Science
11 Department of Materials and Earth Sciences > Earth Science > Applied Sedimentary Geology
Date Deposited: 17 Jun 2015 06:52
License: [undefiniert]
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