Mapping of Fault and Hydrothermal System beneath the Seulawah Volcano Inferred from a Magnetotellurics Structure

Abstract

Magnetotellurics (MT) is an important geophysical method for exploring geothermal systems, with the Earth resistivity obtained from the MT method proving to be useful for the hydrothermal imaging changes of the system. In this research, we applied the MT method to map the geothermal system of the Seulawah Agam volcano in northern Sumatra, a site intended for the construction of a geothermal power plant with an estimated energy of 230 Mwe. Herein, 3D MT measurements were carried out, covering the entire area of the volcano and the various intersecting local faults from the Seulimeum segment in the NW–SE direction. Based on Occam 2D inversion, a conductive anomaly (<10 ohm·m) near the surface was identified in response to specific manifestation areas, including the Heutsz crater on the northern side and the Cempaga crater on the southern side. A further conductive anomaly was also found at a depth of 1 km, which was presumably due to a clay cap layer covering the fluid in the reservoir layer below the surface, where the manifestation areas are formed at various locations (where faults and fractures are found) owing to the fluid in the reservoir rising to the surface. The MT modeling also revealed that the reservoir layer in Seulawah Agam lies at a depth of 2 km with a higher resistivity of 40–150 ohm·m, which is the main target of geothermal energy exploration. At the same time, the heat source zone where magma is located was estimated to lie in two locations, namely, on the northern side centering on the Heutsz crater area and the southern side in the Cempaga crater area. A clear 3D structure obtained via Occam inversion was also used to visualize the hydrothermal flow in the Seulawah Agam volcano that originates from two heat source zones, where one structure that was consistent across all models is the conductive zone that reaches a depth of 5 km in the south in response to the regional faulting of the Seulimeum segment. Based on the MT research, we concluded that the volcano has the geothermal potential to be tapped into power plant energy in the future.

Geothermal reservoir depth of Seulawah Agam volcano estimated from 1D magnetotelluric

“…The volcanic activity is characterized by several traces of manifestation indicating the presence of geothermal energy in a certain geological condition of subsurface rocks [43], [44]. SeulawahAgam volcano has seven manifestations, two of which are craters, namely Heutz crater on the Northside and Ceumpaga Crater on the South of the volcano [15], [29]. Others, such as IeJue and IeSuum in Krueng Raya, Aceh Besar, appear in the form of hot springs and warm ground.…”

“…The magnetotelluric (MT) survey provides an understanding of shallow to deep geological features. Because of the sensitivity of electrical conductivity and its depth investigation, MT is an important tool for geothermal exploration [27], [29]. Furthermore, the MT method has a much deeper investigation depth than other electromagnetic (EM) methods, which are typically incapable of determining geological features and detecting geothermal reservoirs more significant than 1-2 km.…”

Subsurface Mapping of Fault Structure in the Weh Island by Using a 3d Density of Global Gravity

“…If the optimization process with SVD results in a mismatch between the calculated density data with the measurement data, the Occam optimization would be carried out so that both types of data could be closely matched. The Occam is one of the inversion techniques that can be employed for electromagnetic data [21], [22]. The optimization process would allow error values between the observational and theoretical data to become smaller in their density or dimensions.…”

Geoelectrical model of geothermal spring in Ie Jue Seulawah deriving from 2D VLF-EM and DC resistivity methods

“…In the exploitation process, geothermal is one of the alternative sources known as green energy and only requires a small area for exploration and exploitation compared to conventional energy sources such as oil and gas. In the northernmost of Sumatra, Aceh Province has 20 potential geothermal fields that are potential to be developed by the government, such as the Jaboi volcano on Weh Island [2], Peut Sagoe [3], dan Seulawah Agam [4], [5] with an estimated electrical energy production capacity of 230 Mwe [6]. In addition, other parts of the geothermal site, geothermal sites have begun to be developed into geological-based tourist spots to directly impact the community's economy [7].…”