Hydrogeochemical Characterization as a Tool to Recognize “Masked Geothermal Waters” in Bahía Concepción, Mexico

Pablo Hernández-Morales,Diego Morata,Carlos Green-Ruiz,Jobst Wurl

doi:10.3390/resources10030023

Abstract

Geo-thermalism has been widely recognized on the Baja California Peninsula, especially during the last decade. The current research, carried out on Bahia Concepcion, evidences the existence of geothermal springs, which get recharged mainly by groundwater and seawater. The groundwater can be characterized as Na+-Cl− and Na+-HCO3− type, with a pH value close to neutrality. The slightly more acidic thermal sites presented temperatures between 32 °C and 59 °C at the surface. Based on the relationships of the Cl− and Br−, as well as the B/Cl−, and Br−/Cl− ratios, seawater was recognized as the main source of salinity. The spatial distribution is explained directly through marine intrusion, or via sprays and aerosols within the rainwater. Seawater ratios in thermal springs varied from 62% to 83%, corresponding mainly to shallow inflow, but seawater inputs into the deep thermal reservoir were also recognized. Temperatures in the geothermal deep reservoir were inferred from 114 to 209 °C, calculated through the SiO2 and Na+-K+ geothermometers. In addition to previously reported thermal sites at Bahía Concepción, and based on their elevated temperatures, two new sites were identified. Another five springs do not fulfill the commonly used definition, based on differential temperature, but show the typical hydrogeochemical signature of thermal water. A new approach to identify this low-temperature geothermal-influenced spring water by its hydrogeochemical composition is presented, for which the term “Masked Geothermal Waters” (MGW) is introduced. Our findings increase the area of the geothermal anomaly and, therefore, the potential of geothermal resources. The approach proposed in this research will also be useful to identify more MGW in other coastal areas.

Highlights

Due to hydrocarbon deposit depletion, the need to reduce CO2 release to the atmosphere, as well as international environmental agreements, renewable energies have largely escalated in importance in the world in becoming the future’s energy resources, [1,2]
Interest has increased in medium and low-temperature geothermal sites, which can be used in small-scale power generation and other industrial activities that take direct advantage of the use of the geothermal fluid temperature [6]
The physicochemical results measured in the field indicated that the water from the sampling sites had temperatures ranging from 22 ◦C (CB12) to almost 60 ◦C in the coastal thermal springs (CB14, CB15, and CB16, Figure 1)

Summary

Introduction

Due to hydrocarbon deposit depletion, the need to reduce CO2 release to the atmosphere, as well as international environmental agreements, renewable energies have largely escalated in importance in the world in becoming the future’s energy resources, [1,2]. The environmental importance of these alternative energy sources has been recognized [3,4]. Geo-thermalism is a renewable resource with a significant global occurrence, its use is still incipient compared to other alternative energies. Derived from scientific and technological advances, which allow the reduction of operating costs, its future promises to be interesting, competing with other sources of energy [5]. Based on their usefulness, the research on geothermal resources has focused mainly on the assessment of high-temperature geothermal fields, leaving those of medium and low temperature at a second level of importance. Interest has increased in medium and low-temperature geothermal sites, which can be used in small-scale power generation and other industrial activities that take direct advantage of the use of the geothermal fluid temperature [6]

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Conclusion