Two-Dimensional Inversion Magnetotelluric Investigation of the Pariangan Geothermal Field, Indonesia

Abstract

Abstract Pariangan geothermal field is located in Tanah Datar District, West Sumatera Province, Indonesia. The structure developed in this region is influenced by a large fault that extends through Sumatera from Banda Aceh to the Gulf Semangko in Lampung and also the pattern of radial faults that follow the development of Complex Marapi Volcanism. This study is aimed at delineating the shallow as well as deeper conductive anomalies related to the geothermal system in the Pariangan area. Dimensionality analysis showed a two-dimensional (2D) behavior for the data, and therefore 2D inversion was performed. The result of magnetotelluric (MT) data processing indicates a low resistivity (<15 Ω.m) distribution at depths of 1300-3000 meter, which is interpreted as the caprock. Reservoir rock is indicated by the medium resistivity (15-93 Ω.m) at depths of 1200-3200 m. Below the reservoir the deep reaching conductive anomaly is interpreted as circulating hot fluids which heat up the fluids in the reservoir due to the subduction process. Type of alteration developed in research area are dominated by argillic type characterized by the presence of illite, kaolinite, montmorillonite, dickite, and halloysite; propylitic type characterized by the presence of chlorite, epidote and, quartz; and phyllic type characterized by the presence of sericite, quartz, and chlorite. Basement rock zone is indicated by the high resistivity (93-1000 Ω.m) at the depths of 1500-6000 m. MT in this study shows a powerful geothermal exploration tools because of its sensitivity to image hot saline fluids as zones of high conductivity.

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