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Jurnal Geofisika
Published by Himpunan Ahli Geofisika Indonesia
ISSN : 0854352     EISSN : 24776084     DOI : https://doi.org/10.36435/jgf
Core Subject : Science,
Earth & Planetary Sciences Energy Physics
Jurnal Geofisika [e-ISSN : 2477-6084] is a scientific journal published by Himpunan Ahli Geofisika Indonesia (HAGI). This journal is referenced, each paper was assessed and evaluated by editors and reviewers who are experts in the relevant fields and come from education institutions and industry, both from within and outside the country. The published article covers all science and technology including Geophysics, Meteorology, Oceanography, Geology and Geodesy.
Arjuna Subject : Ilmu Bumi dan Planet (semua kategori) - Geofisika
Articles 100 Documents
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Amplitude Variation with Frequency as Direct Hydrocarbon Indicator for Quick Look and Different Insight of Hydrocarbon Delineation Awal F Mandong; Reza P. A. Bekti; Rino I.A. Saputra
Jurnal Geofisika Vol 19 No 2 (2021): Special Issues | Seismic Quantitative Interpretation |Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i2.517

Abstract

One of the most common and established techniques to identify hydrocarbon presence is by analyzing the amplitude variation with offset (AVO) utilizing the pre-stack seismic data. However, the gather data quality even the availability of pre-stack data could often become an issue. When the seismic wave propagates through a highly attenuating medium (i.e. hydrocarbon-bearing reservoir), it loses its high-frequency content and the dominant frequency tends to slide to the lower frequency. These high-frequency loss phenomena can be used to delineate hydrocarbon-bearing reservoirs using spectral decomposition method. The continuous wavelet transform (CWT) is used to decompose seismic and generate the frequency gather data to analyze the frequency loss due to hydrocarbon presence using gradient analysis. The result from this study shows that the hydrocarbon-bearing zone correlates to the high attenuation is able to be delineated using the Amplitude Variation with Frequency (AVF) analysis method. The hydrocarbon anomaly observed from the AVF analysis result is aligned with the AVO analysis and validated by the water saturation log. The results of this study suggest that AVF analysis method can help to identify as a quick look approach and provide a better confidence level as a direct hydrocarbon indicator when combined with other direct hydrocarbon indicator methods such as AVO method.
Catatan Editorial Seismic Quantitative Interpretation (QI) Adi Widyantoro
Jurnal Geofisika Vol 19 No 2 (2021): Special Issues | Seismic Quantitative Interpretation |Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i2.527

Abstract

Jurnal HAGI memulai penerbitan edisi khusus dengan topik tematik yang mengandung riset akademik dan aplikasi di industri, sehingga penyelesaian masalah fundamental mengenai topik yang dimaksud akan lebih terarah. Edisi khusus perdana dimulai dengan memuat tema interpretasi kuantitatif seismik atau seismic quantitative interpretation (QI) yang berkembang pesat di industri minyak dan gas (migas) dalam beberapa tahun belakangan ini, sebagai alurkerjainterpretasi data seismik yang menjadi data primer dalam proses eksplorasi dan produksi migas. Interpretasi kuantitatif menjadi kunci komunikasi antar disiplin, sebagai alat integrasi data dengan dimensi berbeda, serta diperlukan dalam proses memahami resiko dan ketidakpastian untuk menemukan cadangan migas yang semakin sulit.
Enhancing Low-Frequency Model for Post-Stack Inversion using Geostatistics: A Case Study in Imaging Carbonate Structure Dimas Pramudito; Azhar Harisandi; Rebecca Putri Sinaga; Fitriah Nuraeni
Jurnal Geofisika Vol 19 No 2 (2021): Special Issues | Seismic Quantitative Interpretation |Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i2.519

Abstract

Post-stack model based seismic impedance inversion can be a fast and efficient first step in deriving reservoir properties based on seismic data. It can further be used as an input for quantitative interpretation, however behind that seemingly oversimplified process we should not forget the nature of bandlimited seismic data and how we should carefully extract and model the low-frequency component. In the worst case, the low frequency or background impedance model (LFM) might not even be possibly recovered due to the limited logging data interval. In this paper, we will demonstrate how to create an absolute impedance volume to delineate porous reefal carbonate reservoir that has low acoustic impedance by accurately constructing a low frequency model aided with cokriging. The result is an LFM that can accomodate all available well data but still honoring local geological structures and continuities.
Analisis Parameter Elastisitas Untuk Interpretasi Litologi Dan Fluida Pori Reservoir Batupasir Formasi Intra Gumai Cekungan Sumatera Selatan Eliza Veronica Zanetta; Handoyo Handoyo; Fatkhan Fatkhan; Agus Laesanpura, M.S; Harnanti Yogaputri Hutami
Jurnal Geofisika Vol 19 No 2 (2021): Special Issues | Seismic Quantitative Interpretation |Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i2.508

Abstract

Modulus elastisitas merupakan salah satu parameter yang digunakan untuk identifikasi perbedaan litologi dan fluida pori dalam analisis reservoir batupasir tipis Formasi Intra Gumai di Cekungan Sumatera Selatan. Adapun parameter yang digunakan pada penelitian ini adalah Parameter lame (LMR), Poisson’s ratio dan . Parameter lame adalah parameter elastisitas yang menggunakan Vp dan Vs untuk diturunkan menjadi parameter LambdaRho dan MuRho. LambdaRho sensitif terhadap fluida sedangkan MuRho sensitif terhadap litologi. Poisson’s ratio merupakan pengukuran yang merepresentasikan sifat fisis batuan atau rasio dari strain transversal terhadap strain longitudinal. Teknik analisis ini akan dilakukan pada sumur EL-01. Hasil interpretasi log gamma ray, dan crossplot parameter lame pada kedalaman 1090-1120 m merepresentasikan litologi zona target sandstone. Crossplot antara Poisson’s ratio dan menunjukkan keterdapatan oil sand pada kedalaman 1100-1120 m dengan gas-sand memiliki nilai Poisson’s ratio paling rendah yaitu 0-0,21, oil sand memiliki Poisson’s ratio 0,21-0,34, Poisson’s ratio brine sand 0,34-0,39, Poisson’s ratio shale 0,39-0,45 dan Poisson’s ratio tertinggi yaitu unconsolidated shallow sediment. Sifat petrofisika yang digunakan pada penelitian ini yaitu porositas, densitas, dan . Kombinasi antara sifat petrofisika batuan dan parameter lame dapat menjadi metode optimal untuk memisahkan litologi dan kandungan fluida di dalam batuan reservoir.
Ekstrapolasi Frekuensi Rendah pada Full Waveform Inversion (FWI) dengan menggunakan Deep Learning. Part 1 : Validasi data Sintetik Asido Saputra Sigalingging; Ignatius Sonny Winardhie; Ekkal Dinanto
Jurnal Geofisika Vol 19 No 2 (2021): Special Issues | Seismic Quantitative Interpretation |Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i2.518

Abstract

Kandungan seismik frekuensi rendah sangat berperan penting terhadap hasil inversi pada pemodelan Full Waveform Inversion(FWI). Kehilangan frekuensi rendah dari data seismik akan membuat model akhir FWI sulit untuk konvergen. Penelitian ini melakukan ekstrapolasi frekuensi rendah dengan menggunakan deep learning. Dataset diperoleh dengan melakukan pemodelan ke depan seismik akustik menggunakan finnite difference dari beberapa model P-Wave sintetis. Data seismik hasil pemodelan kemudian dipisah menggunakan filter Butterworth, sehingga diperoleh data seismik dengan frekuensi rendah < 5 Hz, dan frekuensi tinggi > 5 Hz. Data frekuensi tinggi dan frekuensi rendah masing-masing berurutan sebagai input dan output data yang akan digunakan sebagai data latih model deep learning. Model deep learning Multi-Ouput Reggresion yang digunakan dalam penelitian ini yakni Multi-Layer Perceptron(MLP) dan Convolutional Neural Networks(CNN). Evaluasi dan testing yang dilakukan terhadap model deep learning memberikan hasil akurasi yang baik. Berdasarkan hasil validasi akurasi model deep learning yang dilakukan, kedua model deep learning potensial untuk diterapakan pada ekstrapolasi frekuensi rendah data real sebelum dilakukan pemodelan Full Waveform Inversion(FWI).
Pemetaan Respons Dinamik Tanah Dan Pemodelan Struktur Bawah Permukaan Di Wilayah Kertajati Menggunakan Metode Horizontal-To-Vertical Spectral Ratio (HVSR) Firda Haifa Fadhilah; Tedi Yudistira; Yayan Sopyan
Jurnal Geofisika Vol 20 No 2 (2022): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i2.545

Abstract

Abstrak Wilayah Kertajati adalah wilayah yang didominasi oleh kondisi geologi berupa batuan lunak yaitu batuan sedimen Kuarter Bawah (Qos) yang mengalami pelapukan pada sebagian besar daerah penelitian dan adanya kenampakan Endapan Aluvium (Qa) pada sisi tenggara. Kondisi batuan lunak yang berada di atas batuan yang lebih keras akan mengakibatkan amplifikasi saat terjadinya gempa bumi. Hal ini dikarenakan pada barat daya daerah penelitian terdapat Sesar Baribis yang menunjam dari Purwakarta dan Majalengka. Sesar ini juga diperkirakan sempat mengakibatkan gempa paling besar yang pernah tercatat di Pulau jawa yang terjadi pada abad ke-17. Pada penelitian ini, pengolahan data mikrotremor dengan metode Horizontal to Vertical Spectral Ratio (HVSR) diharapkan dapat menjadi suatu upaya mitigasi bencana di wilayah Kertajati mengingat di wilayah tersebut juga telah dibangun Bandar Udara Internasional Jawa Barat (BIJB). HVSR adalah metode seismik yang dapat digunakan untuk mengidentifikasi karakteristik dinamik tanah berupa frekuensi dominan dan amplifikasi, serta dapat menghasilkan gambaran struktur seismik bawah permukaan. Dari hasil pengolahan data yang telah dilakukan diperoleh nilai frekuensi dominan bervariasi dengan rentang 0,6-18 Hz sedangkan nilai amplifikasi memiliki rentang 1,26-6,3. Frekuensi dominan bernilai rendah berada pada bagian tengah, barat, dan bagian tenggara dari daerah penelitian, hal ini mengindikasikan ketebalan lapisan sedimen yang relatif lebih besar. Sedangkan nilai amplifikasi bernilai tinggi dominan berada pada bagian tengah dan sisi utara dari daerah penelitian. Pada tahap selanjutnya, dilakukan inversi kurva HVSR menggunakan metode Neighbourhood Algorithm (NA) untuk mengetahui informasi nilai bawah permukaan yang kemudian diasosiasikan dengan karakteristik lapisan soil bawah permukaan. Diperoleh nilai berkisar antara 53-3027 m/s untuk rentang kedalaman hingga 610 m, dengan nilai relatif lebih rendah pada sisi tengah, tenggara, dan barat laut, daerah penelitian. Dilakukan juga pengelompokan jenis tanah dengan nilai rata-rata kecepatan gelombang hingga kedalaman 30 m yang menunjukkan jenis tanah wilayah Kertajati berupa tanah sedang (SD) dan tanah padat atau batuan lunak (SC). Kata kunci: amplifikasi, frekuensi dominan, HVSR. jenis tanah, , Abstract Kertajati area is an area dominated by geological features in the form of soft rocks, namely Lower Quaternary sedimentary rocks (Qos) which have weathered in most of the research area and the appearance of Alluvium Deposits (Qa) on the southeast side. The condition of soft rock that is on top of the harder rock will result in amplification during an earthquake. Because in the southwest of the study area there is the Baribis Fault that subducts from Purwakarta and Majalengka. In this study, microtremor data processing with the Horizontal to Vertical Spectral Ratio (HVSR) method is expected to be a disaster mitigation effort in the Kertajati area considering that the area has also been built West Java International Airport (BIJB). HVSR is a seismic method that can be used to identify dynamic characteristics of the soil in the form of dominant frequency and amplification, and can produce an image of the subsurface seismic structure. From the results of data processing that has been carried out, the dominant frequency values ​​vary in the range of 0.6-18 Hz while the amplification values ​​have a range of 1.26-6.3. The dominant low-value frequencies are on the southeast, southwest, and central part of the study area, indicating a relatively larger thickness of the sediment layer. While the high value amplification values ​​are dominant on the north, southwest, and central parts of the study area. Then the inversion of the HVSR curve was carried out using the Neighborhood Algorithm method to find out the information on the subsurface value which was then associated with the characteristics of the subsurface layer. The values ​​of ranged from 33-3027 m/s for a depth range of up to 610 m, with relatively lower values ​​on the south, northwest, and central parts of the study area. Soil types were also grouped with an average value of wave velocity to a depth of 30 m which indicated the soil types in the Kertajati area were medium soil (SD) and solid soil or soft rock (SC). Keywords: amplification, HVSR, predominant frequency, soil type, Vs30, Vs
Analisis Statistik Distribusi Kejadian Gempabumi Di Luwu Timur, Morowali, Dan Morowali Utara, Sulawesi Imanuela Indah Pertiwi
Jurnal Geofisika Vol 20 No 1 (2022): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i1.477

Abstract

The tectonic conditions of East Luwu, Morowali and North Morowali, which are very complex, are traversed by main and local faults, making it possible to cause large earthquakes with a strength of M≥5. This research was conducted with the aim of knowing the distribution statistics of earthquakes in East Luwu, Morowali and North Morowali. The research area was selected at 1,00oS – 3,50oS dan 120,50oE– 122,50oE. The data used is the earthquake parameter data from IRIS-DMC (Incorporated Research Institutions for Seismology Data Management Centre) earthquake catalog from 1961 to 2020. The Poisson distribution method used in the analysis of the distribution of large earthquakes, produces a graph which shows that the actual Pr% value is above the theoretical Pr% Poisson, which means that the occurrence of large earthquakes (M≥5) in the East Luwu, Morowali and North Morowali areas did not occur in the ungroups type. The spatial distribution of the b-value shows a high value in the East Luwu and Morowali areas compared to the North Morowali area. Statistically, the value of the seismicity index and the probability of an earthquake event in East Luwu, Morowali, and North Morowali decrease as the magnitude of the earthquake increases. It is inversely proportional to the rapid recurrence time in earthquakes with a magnitude M≥5 and a long recurrence time at a greater magnitude.
Multibeam Bathymetric Measurements for Shallow Seabed Features Mapping using Unmanned Surface Vehicle Arif Nugroho; Roynardus Sijabat; Achmad Muzni Chasanudin; Isa Adi subagjo
Jurnal Geofisika Vol 20 No 2 (2022): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i2.546

Abstract

Subsea pipelines are constructions of pipelines laid onto or embedded into the seabed used for the distribution of fluids such as gas or oil. Over time, changes in the morphological seabed around the pipeline area possibly caused by natural processes such as erosion, scouring, or other geological anomalies may potentially lead to pipeline failure due to the presence of pipe anomalies in the form of free-spanning pipes. In general, this phenomenon occurs in pipelines with a dynamic sedimentation environment caused by tidal changes or underwater currents. Pertamina Hulu Mahakam (PHM) performs regular pipeline inspection as part of the pipeline maintenance program. Visual methods via underwater camera and acoustic methodology such as bathymetry were used to obtain the seabed pattern as well as underwater objects. The Mahakam pipeline networks extend from very shallow waters within the river delta area offshore at a depth more than 100m. For very shallow environments where manned vessels have a limited access, bathymetric measurements were done using Multibeam Echosounder (MBES) installed on an Unmanned Surface Vehicle (USV), controlled and monitored via radio communication over a certain distance. In 2021, PHM, in collaboration with Elnusa, conducted a pipeline inspection survey on one of the pipes, with a diameter of 24 inches and a length of 109 meters.. The results of the bathymetric measurements using the USV demonstrated that no indication of the presence of free-spanning pipelines could be found in the underwater vicinity. The depth of the river varied from -1.2 meters to 2.7 meters (Chart Datum). The topographical conditions showed a sloping riverbed with a maximum slope of 12°-13° from the direction fo the floodplain area towards the center of the river/main channel. Seven (7) pockmarks were identified around the pipeline having a diameter of about 29 to 52 cm and a depth of about 6 to 20 cm. In addition, attention should be paid to the possible presence of gas seepage in the pockmarks area, interpreted from the image of reflected acoustic waves in the water column captured by the MBES equipment. Keywords: Pipelines, bathymetry, seabed, MBES, USV
Koreksi Akusisi Ocean Bottom Node (OBN) menggunakan First Break Positioning dan Hodogram: Studi Kasus Akuisisi Seismik 3D XRAY OBN, Offshore North West Java Permana Citra Adi; Yayat Supriyatna
Jurnal Geofisika Vol 20 No 1 (2022): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i1.507

Abstract

We present the result of applying a least square inversion approach and particle motion analysis on direct arrival wave to estimate-related error associated with ocean bottom nodes (OBN) positioning and Geophone orientation. The initial Nodes coordinates are based on acoustic positioning method at the time of deployment and before retrieval. These positions are computed on the assumption a constant water velocity which was measured directly by logging tool sound velocity profile (SVP) and therefore there are possible to have a small error in the node positions. A few nodes demonstrated excessively high shifts due to dragged by fishing net and although the node has censor to measure the Geophone orientation, some of them were not optimally re-orientated to acquisition orientation reference. Failing to correct for these errors could lead to artifacts in the velocity model, create false structures and infidelity in Geophone data. The result of these corrections on field data can improve P-Wave subsurface image quality and also correct the vector infidelity of Geophone data for S-Wave imaging, so the amplitude and kinematic information on the data is ready to be used for further analysis such as on Quantitative Interpretation (QI). Keywords: OBN, positioning, Geophone orientation, vector fidelity
Hasil Awal Analisis Peak Ground Acceleration di Bali Gandini, D. R. A; Setiawan, Y A; Madrinovella, I; Abdullah, A; Pranata, B; Suhardja, S K; Aisy, S R
Jurnal Geofisika Vol 20 No 2 (2022): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v20i2.535

Abstract

Wilayah Bali merupakan daerah dengan tingkat seismisitas yang tinggi karena terletak di Zona Subduksi antara Lempeng Indo-Australia dan Eurasia (selatan) serta adanya struktur back arc thrust (utara). Gempa Bumi Seririt yang terjadi pada tanggal 14 Juli 1976 dengan magnitudo 6,2 SR merupakan salah satu gempa paling merusak di Bali. Oleh karena itu perlu dilakukan upaya mitigasi untuk melihat tingkat potensi bahaya bencana gempa bumi di wilayah Bali. Peak Ground Acceleration (PGA) merupakan pendekatan yang dapat dilakukan dengan cara menentukan intensitas seismik dari gempa bumi di suatu wilayah sehingga dapat diperkirakan risiko paling parah yang dapat dihasilkan dari suatu kejadian gempa bumi. Perhitungan nilai PGA dapat dilakukan melalui suatu pendekatan rumus empiris atenuasi khusus wilayah tertentu. Data yang digunakan berasal dari katalog gempa bumi ISC (1970-2019), USGS (1963-2019), dan data rekaman accelerograph BMKG (2012-2016) di wilayah Bali. Rumus empiris atenuasi dipilih dengan mempertimbangkan jenis gempa bumi dominan dan kondisi geologi di wilayah Bali. Terdapat 3 rumus empiris atenuasi yang digunakan yaitu oleh McGuire (1977), Donovan (1973), dan Esteva & Villaverde (1973). Rumus empiris atenuasi oleh McGuire (1977) menghasilkan nilai error terkecil berdasarkan perbandingan nilai PGA observasi dan nilai PGA kalkulasi. Analisa tingkat potensi risiko akibat gempa bumi dapat dilakukan berdasarkan peta percepatan tanah maksimum dan peta intensitas seismik maksimum di Wilayah Bali. Kabupaten Buleleng dan sekitarnya serta daerah paling timur dari Kabupaten Karangasem merupakan wilayah yang berpotensi terkena dampak paling parah jika terjadi gempa bumi bersifat merusak, sedangkan daerah paling selatan dari Pulau Bali memiliki dampak yang relatif ringan jika terjadi gempa bumi yang bersifat merusak.

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