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"[ABSTRAKTelah diakukan penelitian guna mendelineasi zona prospek sistem panasbumi Daerah „P‟ menggunakan pemodelan multi dimensi data magnetotelurik terintegrasi data geologi dan geokimia. Daerah panasbumi „P‟ secara fisiografi termasuk pada Busur Banda Dalam tak bergunungapi disusun oleh komplek batuan malihan sekis berumur Perm-Trias. Gejala adanya sistem panasbumi pada daerah penelitian ditandai dengan kemunculan manifestasi permukaan berupa enam mata air panas bersuhu (37-67oC), pH (6-7) dan bertipe klorida-bikarbonat. Pembentukan sistem panasbumi diduga berkaitan dengan aktivitas tektonik kuat akibat tumbukan lempeng Pulau Seram dengan Lempeng Benua Australia (Plate Collision) yang memicu pembentukan batuan intrusi di kedalaman sebagai sumber panas. Guna mengetahui informasi subsurface daerah penelitian, dilakukan survei magnetotelurik. Selanjutnya hasil dari data MT akan diintegrasikan data geologi dan geokimia. Pengolahan data MT dimulai dari time-series data hingga mendapatkan kurva resistivitas-frekuensi dan fase, lalu dilakukan filtering noise, rotasi arah strike dan koreksi static shift untuk mendapatkan kualitas kurva MT baik. Selanjutnya dilakukan pemodelan inversi 1D, 2D dan 3D. Temperatur reservoir diduga sekitar 160-180oC termasuk temperatur sedang. Hasil penelitian ini memperlihatkan lapisan konduktif (<15 Ωm) dengan ketebalan ± 500-1000 m diindikasikan sebagai Clay Cap dari sistem panasbumi. Zona resistivitas tinggi (>300 Ωm) dan berbentuk updome, berada di bawah area kemunculan manifestasi (MAP1, MAP2, MAP3, MAP4, dan MAP5) mengindikasikan heat source berada di utara kemudian menerus ke arah tenggara membentuk updome. Model konseptual terpadu sistem panasbumi dibentuk dari integrasi data geologi, geokimia, dan geofisika. Sistem panasbumi daerah penelitian merupakan hidrotermal heat sweep plate collision dengan temperatur sedang, luas area prospek dan rekomendasi titik pemboran diperkirakan ± 3 km2 di sekitar zona Upflow, potensi sumber daya hipotetik dengan metode volume lump parameter menggunakan binary cycle ± 34 MWe.

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ABSTRACTA study for delineating geothermal system of prospect area “P” has been done by using multi-dimensional modeling of magnetotelluric data. Physiographycally, geothermal prospect of “P” area is located at non-volcanic Banda inner arc hosted by Malihan Sekis rock complex with Perm-Trias age. The existance of geothermal system in this area is indicated by the presence of thermal manifestations in form of 6 chloride-bicarbonate hot springs with temperature in the the range of 37 – 67oC, and pH of 6-7. The development of geothermal system is most probably associated with strong tectonic activity caused by the collision between Seram island plate and Australian plate that ignite the occurence of intrussive body as heat source. In order to know the subsurface information of prospect area, magnetotelluric (MT) survey has been done. The processing of MT data was started from time-series data, continued by noise filtering, rotation of strike orientation and static shift correction to obtain better MT curve. The data were then being inversed by means of 1-Dimensional, 2-Dimensional and 3-Dimensional inversion methods. Reservoir temperature is estimated to be around 160-180 oC and classified as moderate temperature. The result of MT data inversions shows the presence of conductive layer (<15 Ωm) with 500 – 1000 m thickness that is interpreted as clay cap og geothermal system. High resistivity zone (>300 Ωm) with updome shape appears underneath the manifestations occurence (MAP1, MAP2, MAP4, and MAP5), indicating that the heat source is located in northern part and elongate to souteast direction. The conceptual model of geothermal system was built based on integrated interpretation of geological, geochemical and geophysical data. The prospect area and recommendation of drilling location is estimated to be ± 5 km2 around upflow zone. Potential hypothetical resource with volume lump parameters method using binary cycle ± 34 MWe., A study for delineating geothermal system of prospect area “P” has been done by using multi-dimensional modeling of magnetotelluric data. Physiographycally, geothermal prospect of “P” area is located at non-volcanic Banda inner arc hosted by Malihan Sekis rock complex with Perm-Trias age. The existance of geothermal system in this area is indicated by the presence of thermal manifestations in form of 6 chloride-bicarbonate hot springs with temperature in the the range of 37 – 67oC, and pH of 6-7. The development of geothermal system is most probably associated with strong tectonic activity caused by the collision between Seram island plate and Australian plate that ignite the occurence of intrussive body as heat source. In order to know the subsurface information of prospect area, magnetotelluric (MT) survey has been done. The processing of MT data was started from time-series data, continued by noise filtering, rotation of strike orientation and static shift correction to obtain better MT curve. The data were then being inversed by means of 1-Dimensional, 2-Dimensional and 3-Dimensional inversion methods. Reservoir temperature is estimated to be around 160-180 oC and classified as moderate temperature. The result of MT data inversions shows the presence of conductive layer (<15 Ωm) with 500 – 1000 m thickness that is interpreted as clay cap og geothermal system. High resistivity zone (>300 Ωm) with updome shape appears underneath the manifestations occurence (MAP1, MAP2, MAP4, and MAP5), indicating that the heat source is located in northern part and elongate to souteast direction. The conceptual model of geothermal system was built based on integrated interpretation of geological, geochemical and geophysical data. The prospect area and recommendation of drilling location is estimated to be ± 5 km2 around upflow zone. Potential hypothetical resource with volume lump parameters method using binary cycle ± 34 MWe.]"

"Daerah penelitian AA merupakan area potensi panasbumi yang cukup prospek dan memiliki manifestasi berupa Fumarol yang memiliki temperatur 90 oC dan beberapa mata air panas yang memiliki temperatur permukaan antara 30-60 oC. Ditinjau dari informasi geologi, area ini memiliki basement batuan tersier yang ditutupi oleh produk lava andesit dan tufaan jaman kuarter. Bentukan geologi yang muncul pada area ini berupa kaldera dan beberapa struktur utama berarah NE-SW sebagai pengontrol aliran fluida menuju manifestasi. Sedangkan, struktur lokal yang membatasi area prospek dapat diidentifikasi oleh beberapa atribut dari metode Geofisika Magnetotellurik dan Gravitasi. Atribut metode Magnetotellurik dapat menghasilkan informasi terkait orientasi dominan struktur serta keberadaan zona konduktif, sedangkan atribut metode Gravitasi digunakan untuk mengetahui jenis struktur dan batas kontak dari zona regional dan residual struktur sebagai benda anomali. Dari hasil atribut dan pemodelan kedua metode tersebut beserta data pendukung geokimia, bahwa zona prospek terletak diantara kemunculan manifestasi fumarol di gunung Ambang dengan luasan prospek sebesar 11 km2 dan prediksi temperatur reservoir 260 0C. Area prospek tersebut menjadi rekomendasi sebagai lokasi exploration drilling selanjutnya dengan well output yang tinggi.

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AA research area is a potential and prospect geothermal region. There are some manifestation, fumarol 90 0C and some cool hot springs that has an ambient temperature 30 60 0C. Based on geological information, there is dominantly tertiary sediment basement which are covered by andesite lava products and quartery tufaan. There are caldera and some major structure oriented NNE SSW as geological surface product and controlling some surface manifestations. Whereas, local structure which is located between major structure can be identified by several attributes of Magnetotellurik and Gravity methods. Magnetotelluric attributes can provide about structure orientation and conductive zone relocation while Gravity attributes can also answering about surface Geology structure distribution based on regional residual anomaly. Accordingly, based on integrative analysis and interpretation, prospect area is constrained between the appearance of fumarol and major structure in Ambang mount, which is covered 11km2 and prediction reservoir temperature 260 0C. It rsquo s very useful as a recomendation for the next exploration drilling location with high output well."

"Manifestasi permukaan pada sistem panas bumi dapat menjadi indikator adanya zona permeabel dibawah permukaan. Zona permeabel dalam sistem panas bumi memiliki dua kegunaan yaitu sebagai frakture atau struktur patahan yang dibutuhkan untuk penyedia zona recharge dan discharge fluida ke dalam reservoir dan memiliki peran sebagai pengontrol mobilitas fluida di reservoir. Zona permeabel ini umumnya terbentuk dari proses konduksi dan konveksi termal dari heat source. Zona ini dapat dideteksi dengan indikasi adanya curve splitting data magnetotelurik. Curve splitting terjadi karena adanya perbedaan resistivitas semu kurva sounding TE dan TM. Gelombang elektromagnetik pada mode TE merambat lebih cepat jika medan listriknya sejajar dengan arah strike. Hal ini menyebabkan impedansi batuan akan lebih kecil dibandingkan dengan mode TM serta nilai resistivitas semu kurva TM akan lebih besar. Hasil kurva TE dan TM dari data lapangan dianalisis untuk mengestimasi zona permeabel yang mungkin ada dibawah permukaan. Korelasi antara TE-TM split curve dengan zona permeable selama ini hanya sebatas analisis kualitatif. Penelitian ini mencoba melakukan analisis kuantitatif keberadaan struktur bawah permukaan tersebut. Kami peroleh zona permeabel dengan strike dan dip dari struktur patahan. Hal ini dapat membantu kita dalam merekonstruksi konseptual model sistem panas bumi lapangan 'J'.

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The Surface manifestation on the geothermal systems is expected to be indicator of the permeable zone. These permeable zone in the geothermal system has two important roles as a fracture or the fault structure that is needed to recharge and discharge zones provider of fluid into the reservoir and as a controller the mobility of fluid in the reservoir. Permeable zone is generally formed by thermal conduction and convection from the heat source. This zone can be analyzed due to the splitting of magnetotelluric data curve. Curve splitting occurs because of the differences in the apparent resistivity from sounding of TE and TM curves. Electromagnetic waves in the TE mode propagating more rapidly if the electric field parallel to the direction of the strike. This causes the impedance of the electromagnetic field will be smaller than the TM mode and the value of apparent resistivity from TM curve will be bigger. The results of the TE and TM curves of field data were analyzed to estimate the permeable zone that may exist below the surface. The correlation between TE TM split curve and permeable zone is only qualitative analysis so far. This research try to do a quantitative analysis the existence of subsurface structures. We have obtained the permeable zones with strike and dip of the fault structure. The analysis may help us to be reconstructed the conceptual model of the geothermal system at J field."

"Salah satu wilayah di Indonesia yang memiliki potensi panas bumi adalah wilayah “WS”. Secara umum, tolak ukur keberhasilan dalam menentukan target eksplorasi adalah menemukan zona yang memiliki tingkat temperatur dan permeabilitas yang tinggi. Zona dengan temperatur tinggi berasosiasi dengan keberadaan sumber panas, sedangkan zona dengan permeabilitas tinggi berasosiasi dengan keberadaan struktur patahan yang mengandung fluida. Fokus pada penelitian ini adalah untuk mengidentifikasi struktur patahan di wilayah panas bumi “WS” melalui analisis model data gravitasi dan magnetotelurik. Analisis tersebut nantinya dikorelasikan dengan informasi geologi dan geokimia untuk hasil yang lebih komprehensif. Singkatnya, metode gravitasi digunakan untuk meneliti anomali percepatan gravitasi bumi akibat adanya perbedaan rapat massa batuan penyusun bawah permukaan bumi, sedangkan metode magnetotelurik digunakan untuk menginduksi bumi sehingga dapat mengidentifikasi distribusi resistivitas suatu batuan di bawah permukaan bumi. Hasil pemodelan forward 2D data gravitasi menunjukkan adanya tiga kategori densitas batuan, yaitu densitas 2.40 – 2.60 gr/cc yang diduga sebagai sumber panas, densitas 1.84 – 2.53 gr/cc yang diduga sebagai lapisan penudung, dan densitas 1.21 – 2.31 gr/cc yang diduga merupakan reservoir. Hasil pemodelan inversion 3D data magnetotelurik menunjukkan bahwa terdapat lapisan konduktif yang ditandai dengan warna merah dan diduga sebagai lapisan penudung, lapisan dengan nilai resistivitas sedang yang ditandai dengan warna hijau berada di bawah manifestasi panas bumi dan diduga merupakan reservoir, serta lapisan dengan nilai resistivitas tinggi yang ditandai dengan warna biru pada kedalaman 1000 – 3000 meter lebih yang diinterpretasikan sebagai sumber panas. Berdasarkan model gravitasi dan magnetotelurik, didapati bahwa densitas yang dihasilkan model gravitasi telah sesuai dengan komponen penyusun sistem panas bumi wilayah “WS” yang dihasilkan oleh model magnetotelurik. Hal ini terkonfirmasi melalui batuan penyusun lapisan penudung yang memiliki nilai densitas tidak lebih besar dari densitas sumber panasnya, mengingat lapisan penudung telah mengalami alterasi hidrotermal dan didominasi oleh mineral halloysite dan montmorillonite. Sistem panas bumi wilayah “WS” merupakan gabungan sistem panas bumi vulkanik yang dipengaruhi oleh batuan sedimen, dengan perkiraan temperatur reservoir sebesar 200°C. Dengan demikian sistem panas bumi ini termasuk dalam intermediate temperature system.

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One of the areas in Indonesia that has geothermal potential is the "WS" area. In general, the measure of success in determining exploration targets is finding zones that have high temperature and permeability levels. Zones with high temperatures are associated with the presence of heat sources, while zones with high permeability are associated with the presence of fluid-containing fault structures. The focus of this research is to identify the fault structure in the "WS" geothermal area through the analysis of gravity and magnetotelluric data models. This analysis will later be correlated with geological and geochemical information for more comprehensive results. In short, the gravity method is used to examine the anomaly of the earth's gravitational acceleration due to differences in the mass density of rocks making up the earth's subsurface, while the magnetotelluric method is used to induce the earth so that it can identify the resistivity distribution of a rock under the earth's surface. The results of the 2D forward gravity data modeling show that there are three rock density categories: a density of 2.40–2.60 gr/cc, which is suspected as a heat source; a density of 1.84–2.53 gr/cc, which is thought to be a cover layer; and a density of 1.21–2.31 gr/cc, which is suspected to be a reservoir. The results of 3D inversion modeling of the magnetotelluric data show that there is a conductive layer marked in red and thought to be a capping layer; a layer with moderate resistivity value marked in green is under geothermal manifestations and thought to be a reservoir; and a layer with high resistivity value marked in blue at a depth of 1000–3000 meters that is interpreted as a source of heat. Based on the gravity and magnetotelluric models, it was found that the density produced by the gravity model was in accordance with the components of the geothermal system in the "WS" region produced by the magnetotelluric model. This is confirmed by the rocks that make up the cover layer, which have a density value not greater than the density of the heat source, considering that the cover layer has undergone hydrothermal alteration and is dominated by the minerals halloysite and montmorillonite. The geothermal system in the "WS" region is a combination of volcanic geothermal systems influenced by sedimentary rocks, with an estimated reservoir temperature of 200°C. Thus, this geothermal system is included in the intermediate temperature system."

"Lokasi prospek geotermal Tawau berada sekitar 20 km arah timur laut kota Tawau, Sabah, Malaysia. Daerah ini didominasi oleh batuan vulkanik Pliocene- Quaternary berupa batuan basalt, dacite, tuff dan andesit yang menyebar di sekitar area Gunung Maria dan Gunung Andrassy. Mata air panas pada lokasi ini ditemukan di area Apas Kiri (A1-A4, A5, A8), area Balung (B1, B2), area Tawau (T1, T2) dan area Sungai Jepun (J1, J2). Berdasarkan data geokimia, pusat reservoar geotermal diperkirakan berada di sebelah tenggara Gunung Maria yang meluas ke area Balung. Untuk memverifikasi hal tersebut, dilakukanlah survey Magnetotellurik (MT). Data MT yang diperoleh dari lapangan kemudian diinversi secara multidimensi (2D dan 3D). Inversi 2D dan 3D secara berturut-turut dilakukan dengan menggunakan software WinGlink dan MT3DInv-X. Selanjutnya, hasil inversi MT tersebut diintegrasikan dengan data geologi dan geokimia yang ada sehingga diperoleh sebuah konseptual model sistem geotermal daerah Tawau yang terintegrasi. Pemodelan visualisasi dilakukan dengan menggunakan software Geoslicer-X. Adapun hasil penelitian memperlihatkan bahwa secara umum hasil inversi 2D telah dapat menggambarkan kondisi bawah permukaan. Akan tetapi, hasil inversi 3D ternyata lebih baik dibandingkan dengan hasil inversi 2D dalam hal kesesuaian dengan struktur. Oleh karenanya, integrasi antar keduanya diperlukan untuk menggambarkan kondisi bawah permukaan yang lebih akurat.

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Tawau geothermal prospect is located about 20 km northeast of Tawau City, Sabah, Malaysia. This area is dominated by Pliocene-Quaternary volcanic rocks such as basalt, dacite, tuff and andesitic rock which are spread around the Mt. Maria and Mt. Andrassy. Hot spring in this area appears in Apas Kiri area (A1-4, A5, A8), Balung area (B1, B2), Tawau area (T1, T2) and Jepun River area (J1, J2). Based on geochemistry data, center of geothermal reservoar is assessed beneath the southeastern part of Mt. Maria and may extends to the Balung Area.

Survey Magnetonetotelluric (MT) was carried out to verify that point. The MT data was processed using multidimensional inversion (2D and 3D). The 2D Inversion was done by using WinGlink software, while the 3D Inversion has been carried out using MT3DInv-X software. The result of MT inversion was then integrated with geological and geochemical data to get an integrated conceptual model of geothermal system Tawau. Visualization modelling was performed by using Geoslicer-X software.

The result of this study show, that in general, 2D inversion's result indicates the subsurface condition with good result. But, 3D inversion is actually more better than 2D inversion in describing geological structure. Accordingly, integration of both results is necessary to describe the subsurface condition more acurately."

"Metode MT merupakan metode geofisika yang umum serta unggul yang digunakan dalam eksplorasi panasbumi saat ini. Namun metode ini memiliki tantangan dalam menentukan secara pasti dimana zona konduktif pada suatu daerah melalui hasil inversi 2-D maupun 3-D akibat dari sifat gelombang elektromagnetik (EM) untuk menginduksi lapisan yang bersifat konduktif, sehingga penetrasi gelombang EM menjadi kecil. Tantangan lain yang muncul adalah upaya meningkatkan rasio kesuksesan dalam tahap drilling (drilling success ratio) pada eksplorasi panasbumi. Target drilling erat kaitannya dengan zona rekahan (fracture). Secara umum zona fracture pada sistem panasbumi berasosiasi dengan sesar yang terisi material ataupun fluida yang akan memiliki resistivitas yang rendah atau bersifat konduktif. Dengan menggunakan fungsi transfer geomagnetik atau disebut juga dengan tipper (induction arrows), yaitu fungsi transfer yang menghubungkan medan magnet vertikal (z) terhadap medan magnet horizontal (x dan y) serta diintegrasikan dengan hasil inversi MT, kita dapat menentukan keberadaan anomali konduktif. Analisis induction arrows pada penelitian ini dilakukan dengan menggunakan software WinGlink. Software ini dapat menampilkan arah panah induksi beserta besar panahnya. Induction arrows pada WinGlink dapat ditampilkan dan dianalisis dalam dua tampilan, yaitu Maps induction arrows untuk menganalisis secara lateral dan Pseudo-Section induction arrows untuk menganalisis secara vertikal. Analisis induction arrows serta inversi 2-D telah diaplikasikan pada data riil (Lapangan-X). Hasil analisis induction arrows serta inversi 2-D pada data riil (Lapangan-X), telah sukses diaplikasikan untuk mengetahui posisi struktur utama serta memetakan persebaran anomali konduktif.

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The MT method is an excellent geophysical method commonly used in geothermal exploration. However, the method presents a challenge in pinpointing the conductive zone in an area based on either 2-D or 3-D inversion result, as a consequence of the tendency of electromagnetic (EM) waves to induce currrent in a conductive layer, which leads to low penetration of MT waves into that layer. Another challenge is in improving the drilling success ratio of the geothermal exploration process. The Drilling target is heavily affected by fracture zones. Generally, the fracture zones in a geothermal system are associated with faults containing conductive materials or fluids will having low resistivity. Using the geomagnetic transfer function, also called the tipper (induction arrows), which is a transfer function that correlates the vertical (z direction) magnetic field to horizontal (x and y direction) magnetic fields, along with MT inversion results, we can determine the location of conductive anomaly. Analysis of Induction arrows on this research done on the software WinGlink. This software can display the direction and magnitude of the induction arrow. In WinGlink, Induction arrows can be displayed and analyzed in two viewing modes, namely the Maps of induction arrows for lateral analysis and Pseudo-Section of induction arrows for vertical analysis. Analysis of induction arrows with 2-D inversion, has been successfully applied to real data (X-Field) in locating the main structure and mapping the distribution of the conductive anomalies."

"Aktivitas geotermal pada daerah X telah ditemukan melalui keberadaan manifestasi panas bumi yang sangat impresif di beberapa titik. Beberapa penelitian yang dilakukan di daerah ini bertujuan untuk menemukan lokasi dan karakteristik reservoir utama sistem geotermal yang ada di area prospek. Namun, beberapa hasil interpretasi yang ditemukan ambigu dikarenakan penggunaan metode survei yang tidak tepat. Dalam penelitian ini, model konseptual yang terintegrasi dari metode magnetotellurik, geokimia, dan geologi digunakan untuk mendelineasi zona reservoir, karakteristik fluida reservoir, dan temperatur reservoir. Berdasarkan hasil konstruksi model konseptual, reservoir sistem geotermal di daerah penelitian ini ditemukan menggunakan metode magnetotellurik berada tepat di bawah tubuh gunung A. Keberadaan manifestasi fumarol di puncak gunung A, tepatnya di kawah gunung A yang mengalami perluasan ke arah timur laut dan sebagian ke arah barat laut, memvalidasi hasil ini. Temperatur pada reservoir mencapai 310°C, dengan sumber panas yang berasal dari gunung A muda. Area prospek diperkirakan sekitar 24 km dengan top of reservoir pada elevasi 1000 meter. Berdasarkan hasil ini, pengeboran eksplorasi dengan tipe sumur standard hole direkomendasikan untuk memvalidasi hasil eksplorasi 3G (geofisika, geokimia, geologi), yang akan ditajak pada kedalaman 2000 meter.

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Geothermal activity in area X has been identified through the presence of impressive manifestations of geothermal activity at several points. Several studies conducted in this area aimed to locate and characterize the main reservoir of the geothermal system present in the prospect area. However, some of the interpreted results were ambiguous due to the improper use of survey methods. In this study, a conceptual model integrated from magnetotelluric, geochemical, and geological methods was used to delineate the reservoir zone, fluid reservoir characteristics, and reservoir temperature. Based on the constructed conceptual model, the geothermal reservoir system in this study area was found to be located precisely beneath the base of Mount A using the magnetotelluric method. The presence of fumaroles at the summit of Mount A, specifically in the Kawah Mount A, which is expanding towards the east-northeast and west-northwest, validates these results. The reservoir temperature reaches 310°C, with the heat source originating from the young Mount A. The prospect area is estimated to be approximately 24 km with a top of reservoir at an elevation of 1000 meters. Based on these results, drilling exporation with a standard hole type is recommended to validate the 3G exploration results (geophysics, geochemistry, geology), which will be drilled to a depth of 2000 meters."