Konsentrasi Radon-222 dalam Gas Tanah untuk Deteksi Distribusi Permeabilitas di Daerah Panas Bumi Tampomas, Jawa Barat

Rasi Prasetio; Neneng Laksminingpuri; Evarista Ristin Pujiindiyati

doi:10.55981/eksplorium.2020.5642

Konsentrasi Radon-222 dalam Gas Tanah untuk Deteksi Distribusi Permeabilitas di Daerah Panas Bumi Tampomas, Jawa Barat

Rasi Prasetio, Neneng Laksminingpuri, Evarista Ristin Pujiindiyati

DOI: http://dx.doi.org/10.55981/eksplorium.2020.5642

Abstract

ABSTRAK Daerah upflow dalam sistem panas bumi merupakan daerah dengan permeabilitas yang tinggi sebagai lintasan naiknya fluida panas bumi ke permukaan, yang umumnya ditandai dengan adanya fumarol di permukaan. Gunung Tampomas, Jawa Barat, merupakan salah satu lokasi potensi panas bumi yang memiliki manifestasi berupa mata air panas, namun tidak memiliki fumarol atau steam vent. Zona permeabel atau upflow sulit untuk diidentifikasi. Isotop ²²²Rn merupakan isotop geogenik yang konsentrasinya di dalam gas tanah dapat menunjukkan permeabilitas, baik permeabilitas primer maupun sekunder (struktur). Serangkaian pengukuran ²²²Rn dalam gas tanah telah dilakukan pada 56 titik di sekitar Gunung Tampomas untuk melihat anomali kandungan ²²²Rn dengan menggunakan metode statistik, serta relasinya antara daerah dengan permeabilitas tinggi dengan struktur geologi dan manifestasi panas bumi. Hasil pengukuran dan evaluasi statistik menunjukkan bahwa konsentrasi ²²²Rn terbagi menjadi konsentrasi rendah (latar), konsentrasi tinggi, dan anomali. Nilai latar berada di 16 lokasi berada di bawah 825 Bq/m³, sementara konsentrasi tinggi di 32 lokasi antara 825–7688 Bq/m³ dan anomali di 8 lokasi di atas 7688 Bq/m³. Sebagian besar lokasi dengan konsentrasi ²²²Rn tinggi dan anomali letaknya tidak berdekatan dengan kelurusan struktur, Seluruh pengukuran yang berdekatan dengan mata air panas memiliki konsentrasi ²²²Rn tinggi dan anomali. Mata air panas Ciseupan merupakan pengecualian yang mengindikasikan air panas tersebut keluar secara lateral (outflow). Selain itu, tidak ada indikasi korelasi antara konsentrasi ²²²Rn dengan elevasi lokasi pengukuran. Proses perpindahan ²²²Rn dari reservoir ke permukaan diperkirakan melalui mekanisme gas pembawa yang berasal dari reservoir panas bumi melalui zona permeabel.

ABSTRACT Upflow zone in the geothermal system is a zone with high permeability that serves as a path for geothermal fluid to ascend to the surface, which usually marked with fumarole at the surface. Mount Tampomas, West Java, is a potential geothermal site with some thermal manifestation in the form of hot springs, but no fumarole or steam vent exists. The up-flow or the permeable zone is difficult to identify. 222Rn isotope is a radiogenic isotope that its concentration in soil gas can infer primary permeability as well as secondary permeability (structure). Series of 222Rn measurement in soil gas has been performed from 56 sampling positions around Mount Tampomas to evaluate 222Rn anomaly by a statistical method and its relation with high permeability area, geological structure, and geothermal manifestation. The measurement and statistical evaluation results show that 222Rn concentration clustered into low (background), high, and anomaly concentration. The background values in 16 places are below 825 Bq/m3, while a high level in 32 areas between 825–7688 Bq/m3 and anomaly in 8 places above 7688 Bq/m3. Most of the locations with high and anomaly 222Rn concentrations did not locate near a structure lineament. All measurements near hot springs have a high 222Rn and anomaly. Ciseupan hot spring is an exception which may indicate that the hot spring is discharged laterally (outflow). Furthermore, there is no indication of a correlation between 222Rn with the elevation of the measurement location. The process of 222Rn transfer from the reservoir to the surface is considered by the geothermal reservoir's gas carrier mechanism through permeable zones.

Keywords

radon; gunung Tampomas; permeabilitas; panas bumi

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