Development of an updated geothermal reservoir conceptual model for NW Sabalan geothermal field, Iran

Abstract

In this paper, a conceptual model has been developed for NW Sabalan geothermal field using exploration indicators. These indicators include the data and results of subsurface and surface investigations comprising geology, geophysics , hydro-geochemistry, hydrology and temperature and pressure distribution. The subsurface information was obtained from 10 deep exploration wells as well as from the results of previous studies in this field. All available data together with the stratigraphy and 1:20,000 geological map covering the study area were combined to produce a two-dimensional geological cross section. Also, a subsurface three-dimensional geological model was developed using available drilling logs. NW Sabalan geothermal field is one of the 18 detected potential areas in Iran that is located in Northwest of the country. This field includes a deep geothermal reservoir with a temperature range of 230–242 °C. The reservoir is covered by a cap rock with an approximate thickness of 500 m. There are four major geological units identified in the study area including Quaternary alluvium, fan and terrace deposits; Pleistocene post-caldera trachyandesitic Flows; Pleistocene syn-caldera trachydacitic to trachyandesitic domes and Pliocene pre-caldera trachyandesitic lavas, tuffs and pyroclastic. A hydraulic conductivity zone has been assessed by magnetotelluric surveys at deeper zones, suggesting that the main outflow direction is towards west and north of the area. The fluid chemistry is consistent with high chloride, neutral pH and immature liquids that partially equilibrated with host rock and they are classified as mixed water. The results of exploration and geological studies during a 10-year period have been integrated together to build a new overall conceptual model of the field.