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INDONESIA
Jurnal RISET Geologi dan Pertambangan
Published by Lembaga Ilmu Pengetahuan Indonesia
ISSN : 01259849     EISSN : 23546638     DOI : -
Core Subject : Science,
Earth & Planetary Sciences
RISET (Indonesian Journal of Geology and Mining) welcomes article submissions dealing with Geology; Applied Geophysics; Mining.
Arjuna Subject : -
Articles 238 Documents
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TWO-DIMENSIONAL INVERSION MODELING OF MAGNETOTELLURIC (MT) SYNTHETIC DATA OF A GRABEN STRUCTURE USING SimPEG Imamal Muttaqien; Jajang Nurjaman
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 31, No 1 (2021)
Publisher : Indonesian Institute of Sciences

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.14203/risetgeotam2021.v31.1121

Abstract

The magnetotelluric (MT) method is a passive exploration method in geophysics that utilizes natural electromagnetic waves as a signal source. MT operates in the frequency range of 10-5 - 106 Hz, designed to study the structure of the conductivity below the earth's surface with a depth range from several tens of meters to the upper mantle. In this paper, 2-dimensional inversion modeling is performed on MT synthetic data using the SimPEG software. First, forward modeling is done by making a 2-dimensional conductivity model in the form of a valley (graben), which aims to produce MT synthetic data in TE (transverse electric) mode, TM (transverse magnetic) mode, and a combination of TE mode and TM mode. Next, an inversion modeling is performed on the MT synthetic data by adding a 5% Gaussian noise and a 10-5 floor as data uncertainty to obtain a 2-dimensional conductivity inversion model. The final result can be validated by comparing the true model and the inversion model and between observational data (synthetic) and predictive predicted data. The results of this study provide a significant fit of the model and suitability of the data. The inversion quality is validated with an RMS Error for TE mode of 0.349%, TM mode of 0.348%, and a combination of TE and TM mode of 0.249%.  
FASIES DAN LINGKUNGAN PENGENDAPAN FORMASI KANIKEH, CEKUNGAN BULA, MALUKU Akhmad Khahlil Gibran; Aries Kusworo
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 30, No 2 (2020)
Publisher : Indonesian Institute of Sciences

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.14203/risetgeotam2020.v30.1108

Abstract

Batuan silisiklastik berumur Trias yaitu Formasi Kanikeh, tersebar di Pulau Seram hingga Pulau Kesui dan Teor dari Maluku hingga Maluku Tenggara. Formasi Kanikeh telah lama dikenal memiliki karakteristik batuan induk yang baik. Pemahaman tentang Formasi Kanikeh masih minim, interpretasi lingkungan pengendapan dan korelasi stratigrafi masih ada perbedaan. Tujuan penelitian ini adalah mendapatkan hasil interpretasi lingkungan pengendapan berdasarkan data terbaru. Metode yang digunakan dalam penelitian ini adalah pengukuran penampang stratigrafi pada empat lintasan pengamatan di daerah Seram Bagian Timur dengan menggunakan pendekatan analisis litofasies dan asosiasi fasies. Hasil dari penelitian ini menunjukkan adanya 9 litofasies, yaitu: Litofasies Batupasir Konglomeratan (Sg); Litofasies Batupasir Lapisan Silangsiur Mangkok (Sp); Litofasies Batupasir Bioturbasi (Sb); Litofasies Batupasir Karbonan (Sc); Litofasies Batupasir Bergelombang (Sw); Litofasies Batupasir Flasser (Sf); Litofasies Batupasir Laminasi Sejajar (Sh); Litofasies Batulumpur Lenticular (Fl); Litofasies Batulumpur Berlapis (Fsc). Deskripsi litofasies tersebut termasuk ke dalam suatu sistem pengendapan pasang-surut (intertidal) yaitu tidal channel, tidal sand flat, tidal sand-mud mixed flat, dan tidal mudflat. Formasi Kanikeh terendapkan dengan sistem pengendapan batuan silisiklastik yang dipengaruhi oleh arus pasang-surut pada lingkungan pengendapan transisi. ABSTRACT - Facies and depositional environment of Kanikeh Formation, Bula Basin, Maluku. The Triassic siliciclastic rocks, Kanikeh Formation are spread across Seram, Kesui, and Teor Island from Molucca to Southeast Molucca. The Kanikeh formation has been known as an excellent source rock. However, its interpretation of the depositional environment and stratigraphic correlation are still poorly understood. This study aims to give a better understanding of the depositional environment. This study consists of Lithofacies descriptions and facies associations of four stratigraphy measuring sections in Eastern Seram Island. The results of this study indicate that there are 9 lithofacies, including conglomeratic sandstone (Sc); Through cross bed sandstone (Sp); Bioturbated sandstone (Sb); Carboniferous sandstone (Sc); Wavy Sandstone (Sw); Flasser Sandstone (Sf); parallel laminated sandstone (Sh); lenticular mudstone (Fl); dan laminated mudstone (Fsc). The lithofacies description is included in four facies associations which are included in a tidal deposition system (intertidal) there are tidal channels, tidal sand flat, tidal sand-mud mixed flat, dan tidal mudflat. Based on the results Kanikeh Formation is deposited with a siliciclastic deposition system influenced by tidal currents within transition deposition environments.
ESTIMASI IMBUHAN AIRTANAH DAS CIDANAU MENGGUNAKAN MODEL NERACA KESETIMBANGAN AIR Gumilar Utamas Nugraha; Priyo Hartanto; Hendra Bakti; Asep Mulyono
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 30, No 2 (2020)
Publisher : Indonesian Institute of Sciences

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.14203/risetgeotam2020.v30.1118

Abstract

Airtanah merupakan faktor penting bagi pembangunan ekonomi di wilayah Serang Barat dan Kota Cilegon, dimana kedua wilayah ini terletak di dalam DAS Cidanau. Selain itu, imbuhan airtanah sangat dibutuhkan untuk memastikan keberlanjutan dan pengelolaan airtanah di suatu wilayah. Penelitian ini bertujuan untuk mengestimasi resapan airtanah DAS Cidanau menggunakan metode Thornthwaite, Dingman, Dingman−Hamon dan Edijatno−Michel. Keempat metode estimasi pengimbuhan airtanah tersebut merupakan metode kesetimbangan air yang berlandaskan model neraca kesetimbangan air. Software ESPERE version 2 digunakan untuk menganalisis kesetimbangan air berdasarkan keempat metode tersebut. Hasil penelitian menunjukkan terdapat tiga klaster nilai imbuhan airtanah di lokasi penelitian yaitu Thronthwaite (157 mm/tahun), Dingman−Hamon (125 mm/tahun), dan Edijatno−Michel (186 mm/tahun). Ketiga perbedaan nilai ini disebabkan oleh adanya perbedaan kalkulasi nilai hujan efektif metode- metode tersebut, dimana metode Dingman dan metode Edijatno−Michel memiliki kecenderungan pola kalkulasi yang sama. Imbuhan airtanah hanya sekitar 7,8 – 11,6 % dari jumlah hujan tahunan yang ada di lokasi penelitian. Sekitar 80 % dari hujan tahunan di konversikan menjadi evapotranspirasi potensial dan sisanya menjadi limpasan permukaan. Dengan mempertimbangkan kondisi geologi - hidrometeorologi Indonesia yang cenderung kompleks, metode Thornthwaite dan metode Dingman−Hamon direkomendasikan untuk perhitungan nilai imbuhan airtanah yang ada di Indonesia.  ABSTRACT − Groundwater Recharge Estimation using Water Budget Method in Cidanau Watershed. Groundwater is an important factor for economic development in West Serang and Cilegon City. These areas are located within the Cidanau watershed. Moreover, groundwater recharge is crucial to ensure the sustainability and the management of groundwater in an area. This study aims to estimate groundwater recharge in the Cidanau watershed using the Thornthwaite, Dingman, Dingman−Hamon, and Edijatno−Michel methods. These four groundwater recharge estimation methods are water budget method based on the water balance model analysis using the ESPERE version 2 software. The results show three clusters of annual groundwater recharge values in the research location, which are Thronthwaite (157 mm/year), Dingman−Hamon (125 mm / year), and Edijatno−Michel (186 mm / year). The three different values were derived from differences in the effective rainfall values calculations in those three methods. The Dingman and the Edijatno−Michel method tend to have a similar calculation pattern. The groundwater recharge is only 7.8 − 11.6 % of the total annual rainfall in the study area. It is estimated that 80% of the annual rainfall is converted into potential evapotranspiration, and the rest becomes surface runoff.
INVERSI GEOSTATISTIK MENGGUNAKAN ANALISA MULTI-ATRIBUT STEPWISE REGRESSION UNTUK KARAKTERISASI RESERVOIR Rahmat Catur Wibowo; Suci Ariska; Ordas Dewanto
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 30, No 2 (2020)
Publisher : Indonesian Institute of Sciences

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.14203/risetgeotam2020.v30.1088

Abstract

Eksplorasi dan produksi pada reservoir tight sand sampai saat ini masih memiliki tantangan tersendiri karena karakterisitik porositas dan permeabilitas yang rendah. Penelitian ini dilakukan untuk menganalisis karakteristik reservoir tight sand berdasarkan peta persebaran properti log menggunakan inversi impedansi akustik (IA) dan analisis multi-atribut. Analisis multi-atribut stepwise regression adalah suatu metode yang menggunakan atribut-atribut yang paling baik untuk memprediksi log target dengan melalui proses trial and error. Pemilihan atribut seismik yang tepat dapat memberikan penggambaran zona target yang lebih baik. Penelitian ini dilakukan untuk memperoleh peta struktur geologi bawah permukaan, volume impedansi akustik. Kemudian dilakukan analisis multi-atribut untuk mendapatkan prediksi volume property log yang mencakup pseudo gamma-ray, densitas, dan porositas dengan menggunakan metode stepwise regression. Hasil inversi seismik IA dan analisis multi-atribut stepwise regression menunjukkan reservoir dengan fluida berupa gas, serta litologi tight sand yang memiliki rentang nilai IA sebesar 22.000 ((ft/s)*(g/cc)) sampai dengan 45.000 ((ft/s)*(g/cc)), densitas 2,25 g/cc sampai dengan 2,6 g/cc, dan porositas 5% sampai 12%. Peta densitas dan porositas yang diperoleh dari analisa multi-atribut menunjang tahap eksplorasi dan produksi jangka panjang. Hal tersebut terkait upaya untuk meningkatkan pemahaman tentang perangkap stratigrafi, dan kemenerusan lapisan reservoir. ABSTRACT – Geostatistical Inversion Using Multi-attribute Stepwise Regression for Reservoir Characterization. Exploration and production of tight sand reservoirs are still challenging due to their low porosity and permeability characteristics. This study used acoustic impedance inversion and multi-attribute analysis to analyze the tight sand reservoir characteristics based on the log property distribution map. Stepwise regression multi-attribute analysis is a method that uses the best attributes to predict the target log, which is carried out through a trial and error process. The ability to select a correct seismic attribution can provide a better depiction of the target zone. This research was conducted to obtain a subsurface geological structures map, acoustic impedance volumes. The multi-attribute analysis was performed to predict volume log properties such as pseudo-gamma-ray, density, and porosity, by using the stepwise regression method. The results of acoustic impedance seismic inversion and stepwise regression multi-attribute analysis show that the reservoir contains gas fluid with tight sand lithology, which has a range of acoustic impedance values of 22,000 ((ft/s)*(g/cc)) to 45,000 ((ft/s)*(g/cc)), the density of 2.25 g/cc to 2.6 g/cc, and porosity of 5% to 12%. The density and porosity maps obtained from the multi-attribute analysis can support the long-term exploration and production stages. The aims are to improve the primary recovery and tertiary recovery, understanding the stratigraphic traps, and the continuity of reservoir layers.
CHARACTERIZATION OF ROCK LAYERS BASED ON REFRACTION SEISMIC METHOD: A CASE STUDY OF MENTARANG’S HYDRO-POWER PLANT, MALINAU REGENCY, NORTH KALIMANTAN Wisnu Slamet Priyanto; Jauhari Arifin
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 31, No 1 (2021)
Publisher : Indonesian Institute of Sciences

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.14203/risetgeotam2021.v31.1160

Abstract

North Kalimantan Province is a new province that is dynamic in development in order to prosper the inhabitants. The research and exploration to make a plan to develop new renewable energy are one of their main programs. The hydro-power plant of Mentarang, Malinau Regency, Kalimantan Utara is a plan program in 2020. The research study of hydro-power plants is essential as a reference in the development plan and avoids the hazard, miss calculation due to human error, etc. Seismic refraction is used in the feasibility study and detailed engineering study (FS DED) of Mentarang's Hydro-power plant. Analysis from the Seismic refraction method can be used as an input parameter for deciding the feasibility of Mentarang's hydro-power plant. This study aims to characterize the sub-surface layers, structure, and sub-surface layer thickness within this area. The seismic refraction method uses the intercept time or travel-time versus distance and processed using the reciprocal method, then it is modelled using inversion and resulted in a 2D profile. This research study was used the seismic refraction method with geometry acquisition of 14 sources with two spread and 5 meters of geophone interval.  The analysis result of the 2D inversion profile model, in general, is classified as four strata layers. These strata are categorized as weathered layers with 5-15 meters of thickness, clay, and Sandstone about 5-20 meter of layer thickness, Sandstone with the layer thickness of about 20-50 meters, and lastly, granite, lava rocks, or limestone with depth more than 70 meters below the subsurface. There is a possibility of a structure at an offset of 70 meters, but this method's limitation will overestimate the conclusion. Therefore, it is necessary to bring another method that more sensitive to work further in research study evaluation of hydro-power plant Mentarang, Malinau Regency, North Kalimantan. 
COVER DEPAN Vol 31 No 1 Juni 2021 riset geotam
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 31, No 1 (2021)
Publisher : Indonesian Institute of Sciences

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.14203/risetgeotam2021.v31.1184

Abstract

COVER DEPAN
COVER DEPAN Vol 31 No 2 Desember 2021 AndriCOVER DEPAN Vol 31 No 1 Juni 2021 Agus Rahman
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 31, No 2 (2021)
Publisher : Indonesian Institute of Sciences

Show Abstract | Download Original | Original Source | Check in Google Scholar

Abstract

Geothermal Reservoir Identification based on Gravity Data Analysis in Rajabasa Area- Lampung Muh Sarkowi; Rahmat Catur Wibowo
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 31, No 2 (2021)
Publisher : Indonesian Institute of Sciences

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.14203/risetgeotam2021.v31.1164

Abstract

Gravity research in the Rajabasa geothermal prospect area was conducted to determine geothermalreservoirs and faults as reservoir boundaries. The research includes spectrum analysis and separation of the Bouguer anomaly to obtain a residual Bouguer anomaly, gradient analysis using the second vertical derivative (SVD) technique to identify fault structures or lithological contact, and 3D inversion modeling of the residual Bouguer anomaly to obtain a 3D density distribution subsurface model. Analysis was performed based on all results with supplementary data from geology, geochemistry, micro-earthquake (MEQ) epicenter distribution map, and magnetotelluric (MT) inversion profiles. The study found 3 (three) geothermal reservoirs in Mount Balirang, west of Mount Rajabasa, and south of Pangkul Hot Spring, with a depth of around 1,000-1,500 m from the ground level. Fault structures and lithologies separate the three reservoirs. The location of the reservoir in the Balirang mountain area corresponds to the model data from MEQ, temperature, and magnetotelluric resistivity data. The heat source of the geothermal system is under Mount Rajabasa, which is indicated by the presence of high-density values (might be frozen residual magma), high-temperature values, and the high number of micro-earthquakes epicenters below the peak of Mount Rajabasa.
Wireline logs vs drilling events: Which one to believe in implying subsurface pressure? Agus Mochamad Ramdhan; Arifin Arifin; Rusmawan Suwarman
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 31, No 2 (2021)
Publisher : Indonesian Institute of Sciences

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.14203/risetgeotam2021.v31.1176

Abstract

As generally known, subsurface pressure can be implied using both wireline logs and drilling events. However, there may be a case where wireline logs and drilling events do not indicate the same subsurface pressure. Data from four vertical wells located in the South Sumatra Basin, Indonesia, were analyzed as a case study. Two wells, Wells A and D, encountered high overpressured zones, confirmed by drilling events and wireline logs data. The two others, Wells B and C, only encountered low overpressured zones, inferred by the relatively low mudweight used during the drilling. However, the wireline logs of Wells B and C show a reversal as Wells A and D. There are two hypotheses to explain the condition in Wells B and C. First, the wireline logs reversal is due to shallow carbonate cementation. Second, Wells B and C were drilled in an unintentional underbalanced condition. The method used includes XRD, SEM, and titration analysis. The results show that the first hypothesis is false, while the second is true. It may be due to some missing information related to drilling events in the final well report of Wells B and C.
Depositional Environmental Evolution of Nyalindung Formation based on Paleontology Molluscan Study, Ciodeng Area, Sukabumi, West Java, Indonesia Aswan Aswan; Elina Sufiati
JURNAL RISET GEOLOGI DAN PERTAMBANGAN Vol 31, No 2 (2021)
Publisher : Indonesian Institute of Sciences

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.14203/risetgeotam2021.v31.1181

Abstract

This research was conducted to understand and identify changes in the depositional environment of the Nyalindung Formation in the Ciodeng area, Sukabumi, based on mollusk paleontology and lithological associations. Paleontological study of mollusks to interpret the depositional environment becomes important due to the scarcity or absence of foraminifera in mollusk bearing rocks. Foraminifera is commonly used to determine depositional environment. The results of this mollusk paleontology study and lithological associations show at least sixteen changes in depositional environment. The environmental changes range from rivers, mangroves, beaches, tidal areas, shallow marine nearby the coast, shallow open marine, and relatively deeper marine. The depositional environmental changes shown by thissection might be related to tectonic activity and global sea level fall that occurred since the early Late Mioceneto Pleistocene. The sedimentary units in this section are also characterized by predominant fluvial, mangroves, beach, and tidal in the upper layers. 

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