New Insights into Hydrothermal Fluid Circulation Affected by Regional Groundwater Flow in the Asal Rift, Republic of Djibouti

Abdek Hassan Aden,Bernard Sanjuan,Bernard Giroux,Jasmin Raymond

doi:10.3390/en14041166

Abdek Hassan Aden, Bernard Sanjuan + Show 2 more

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https://doi.org/10.3390/en14041166

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Abstract

The Asal Rift hosts a lake located in a depression at 150 m below sea level, where recharge is influenced by regional groundwater flow interacting with the Ghoubbet Sea along the coast of Djibouti. This regional groundwater flow is believed to influence hydrothermal fluid circulation, which we aim to better understand in this study, having the objective of developing concepts for geothermal exploration in the area. To this end, magnetotelluric data acquired in the Asal Rift were processed and analyzed. 1D inversion models of electrical conductivity were interpolated for interpretation. These data were then used to build a 2D hydrogeological model, allowing multiphase flow and heat transfer simulations to be performed, considering the regional groundwater flow near the surface and the site topography, in order to confirm the preferred path of fluid flow. Geophysical data analysis indicates the presence of normal faults, notably the H fault, which may act as a conduit for the circulation of hydrothermal fluids and where the hanging wall can be a hydrogeological barrier within the hydrothermal system of the Asal Rift. The results from the 2D numerical flow and heat transfer modelling show the importance of groundwater flow responsible for thermal springs located at the periphery of Asal Lake. Reservoir temperature inferred by means of geothermometry ranging from 200 to 270 °C was shown to correspond to simulated temperature at potential reservoir depth. Moreover, simulated temperature between 600 and 1700 m depth is close to the temperature profile measured in the geothermal well Asal 6 of the area, with less than 20 °C difference. Simulations indicate that hydrothermal fluid circulation is likely influenced by the regional groundwater flow controlled by the topography and the major water bodies, the Ghoubbet Sea and Asal Lake, feeding buoyant fluids interacting with a deep magmatic source and where tectonic activity created normal faults offering a preferred path for fluid circulation.

Highlights

Introduction published maps and institutional affilExtensive tectonic environments are known to host significant geothermal resources with large-scale fluid flows [1]
Observed and simulated electrical resistivity fits with an average root mean square Observed and simulated electrical resistivity fits with an average root mean square (RMS) misfit of about 0.1
This study emphasizes the importance of fault activity and its role in hydrothermal circulation

Summary

Introduction

Introduction published maps and institutional affilExtensive tectonic environments are known to host significant geothermal resources with large-scale fluid flows [1]. The Asal Rift is located in the central part of the Republic of Djibouti in the Afar depression, a tectonically active region where three major structures, the Great Rift Valley, the Red Sea, and the Gulf of Aden, are in extension and together form the Afar Triple [2,3], an emerged oceanic rift like that of Iceland. This region is a geological laboratory, where several scientific studies have been conducted to understand the processes and mechanisms related to the rifting phenomenon.

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