2D Modeling of Seulawah Agam Geothermal Field Based on Magnetotelluric (MT) Data

irfan Putra, Nazli Ismail, Marwan Marwan

Abstract


Telah dilakukan pemodelan 2D data Magnetotellurik (MT) di Gunung Api Seulawah Agam. Penelitian ini bertujuan untuk mendapatkan model konseptual lapangan panas bumi Gunung Api Seulawah Agam berdasarkan model resistivitas 2D. Data fungsi transfer MT yang digunakan yaitu dari rentang frekuensi 2,34 - 320 Hz yang terdiri dari 7 titik stasiun pengukuran. Data titik pengukuran terdiri dari nilai intensitas medan listrik dan intensitas medan magnet yang memiliki 28 frekuensi. Total panjang lintasan pengukuran yaitu sepanjang 27,7 km. Lintasan pengukuran memotong Gunung Api Seulawah Agam dari arah Selatan ke Utara. Data hasil pengukuran yaitu berupa nilai resistivitas semu dan fase yang kemudian dimodelkan menggunakan kode REBOCC. Terdapat 3 model yang dihasilkan dari proses inversi data MT menggunakan REBOCC yaitu mode TE, mode TM dan mode TE+TM. Model mode TE+TM merupakan model yang paling bagus karena menghasilkan model yang lebih jelas dan smooth bila dibandingkan dengan model pada mode TE dan mode TM. Hasil model konseptual menunjukkan bahwa pada lapisan pertama yaitu lapisan top soil (lapisan teratas) memiliki nilai resistivitas sebesar 20 - 60 Ω.m, yang terdapat pada jarak 6 - 23 km. Lapisan kedua yaitu lapisan clay/caprock dengan nilai resistivitas relatif rendah yaitu lebih kecil dari 10 Ω.m, yang berada pada jarak 6 - 27,7 km. Lapisan clay/caprock memiliki sifat impermeabel dan konduktif. Selanjutnya lapisan ketiga yaitu lapisan reservoir dengan nilai resistivitas berkisar antara 10 - 100 Ω.m.

 

2D modeling of magnetotelluric data has been conducted at Seulawah Agam volcano. This study aims to obtain a conceptual model of Seulawah Agam geothermal field based on 2D resistivity model. The magnetotelluric data were measured in range of frequency from 2.34 to 320 Hz at 7 stations along a profile crossing the Seulawah Agam volcano. The length of the profile is 27.7 km with a direction from north to south. The apparent resistivity and phase of magnetotelluric transfers function were used for the 2D inversion modelling of REBOCC code. The inversion was carried out using TE-mode, TM-mode and TE+TM-mode to obtain a better model. The model inverted of TE+TM-mode has resolved well, resistivity variation of subsurface of the Seulawah Agam volcano area. The inverted model shows the top later has resistivity values from 20-60 Ω.m, which is interpreted as a top soil. The second layer is a layer of clay/caprock with a relatively low resistivity values of less than 10 Ω.m. The third layer is predicted as reservoir with resistivity values ranging between 10-100 Ω.m.

 

Keywords: magnetotelluric method, resistivity, 2D model, REBOCC code and Volcano Seulawah Agam.


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DOI: https://doi.org/10.24815/jacps.v8i2.12871

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