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ANNOTATION OF USING BOREHOLE TIME-LAPSE GRAVITY BY GENETIC ALGORITHM INVERSION FOR SUBSURFACE MODELING Gunawan, Indra; Wahyudi, Eko Januari; Alawiyah, Susanti; Kadir, Wawan Gunawan Abdul; Fauzi, Umar
Journal of Engineering and Technological Sciences Vol 52, No 2 (2020)
Publisher : Institute for Research and Community Services, Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.eng.technol.sci.2020.52.2.2

We present the annotation to a genetic algorithm (GA) method for an inverse synthetic subsurface density model using surface and borehole time-lapse gravity data. The objective of the inversion is to find the boundaries of the object area and background, where one bit of the chromosome represents the densities. The model that was used in this paper was a simple homogeneous body anomaly and a simplified real water mass injection model in order to argue that the code is suitable for field modeling. We show the influences of the existence of borehole gravity data and location towards the inversion, where the result indicates that an additional good borehole location could increase the success rate up to 13.33% compared to without gravity borehole data for the simple model and up to 4.39% for the field model. The inversion produced the best results when the borehole positions were placed in a state of symmetry towards the body object?s mass.

Annotation of Using Borehole Time-Lapse Gravity by Genetic Algorithm Inversion for Subsurface Modeling Indra Gunawan; Eko Januari Wahyudi; Susanti Alawiyah; Wawan Gunawan Abdul Kadir; Umar Fauzi
Journal of Engineering and Technological Sciences Vol. 52 No. 2 (2020)
Publisher : Institute for Research and Community Services, Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.eng.technol.sci.2020.52.2.2

We present the annotation to a genetic algorithm (GA) method for an inverse synthetic subsurface density model using surface and borehole time-lapse gravity data. The objective of the inversion is to find the boundaries of the object area and background, where one bit of the chromosome represents the densities. The model that was used in this paper was a simple homogeneous body anomaly and a simplified real water mass injection model in order to argue that the code is suitable for field modeling. We show the influences of the existence of borehole gravity data and location towards the inversion, where the result indicates that an additional good borehole location could increase the success rate up to 13.33% compared to without gravity borehole data for the simple model and up to 4.39% for the field model. The inversion produced the best results when the borehole positions were placed in a state of symmetry towards the body object's mass.

Simulasi Numerik untuk Menentukan Gaya Gravitasi Bawah Permukaan Pada Model Prisma Segiempat Indra Gunawan; Susanti Alawiyah
Indonesia Journal on Computing (Indo-JC) Vol. 1 No. 2 (2016): September, 2016
Publisher : School of Computing, Telkom University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.21108/INDOJC.2016.1.2.88

Resolusi model bawah permukaan menggunakan data gaya berat dengan pendekatan prisma segi-empat ditentukan oleh ukuran dari prisma tersebut. Semakin kecil ukuran prisma, maka semakin tinggi resolusi yang dihasilkan. Sayangnya, ukuran dari prisma berkorelasi langsung dengan jumlah prisma pada volume model. Jumlah dari prisma juga akan berhubungan dengan harga komputasi yang harus dibayar untuk menghitung area yang sedang dikaji. Untuk mengatasi hal ini, dalam penelitian ini digunakan beberapa metode perhitungan pemodelan kedepan melalui pendekatan prisma segi-empat sebagai akibat dari model objek massa jenis yang homogen. Selanjutnya dilakukan analisa terhadap efisiensi, akurasi dan kemampuan dari setiap metode menggunakan bahasa pemrograman C++ dengan presisi ganda. Sebagai contoh objek dan titik observasi, digunakan standard cubic model untuk membandingkannya dengan hasil perhitungan. Berdasarkan hasil perhitungan, terdapat beberapa titik observasi yang tidak bisa dihitung karena adanya sifat singularity. Paper ini memberikan informasi benchmark dan review metode berdasarkan pada pengujian yang dilakukan.

PEMODELAN TIME-LAPSE MICROGRAVITY UNTUK ESTIMASI PERUBAHAN MUKA AIRTANAH DI BANDUNG, JAWA BARAT Eko Januari Wahyudi; Wawan Gunawan A. Kadir; Susanti Alawiyah; Setianingsih Setianingsih; Indra Gunawan; Dadi Abdurrahman
JURNAL SUMBER DAYA AIR Vol 19, No 2 (2023)
Publisher : Bina Teknik Sumber Daya Air, Kementerian Pekerjaan Umum dan Perumahan Rakyat

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.32679/jsda.v19i2.858

ABSTRACT Studies related to groundwater monitoring using geophysical methods have been carried out since the 1990s. Surface gavity data with a scheme of relative gravimeter measurements is chosen for monitoring in urban areas because it is quite fast, easy, affordable, and relatively low-impact on the environment. The significance of the time-lapse microgravity method for the target of this study depends on changes in the mass of water in the aquifer layer below the surface. The research area in this study covers the city of Bandung and several surrounding areas with an interpolated grid coverage of (18 x 17) km2. Gravity changes were determined by six repeated surveys at the same observation points from 2010 to 2021. The aim of this research is to develop a method for estimating groundwater table changes based on time-lapse microgravity data modeling. The complexity of subsurface density changes is simplified for two parts related to near surface density changes and density changes in the intermediate aquifer layer. The trend of groundwater table data in 2010 is used as a reference to determine estimates for 2015, 2016 (February and August), 2019, and 2021. Modeling results for intermediate aquifers (confined groundwater system) provide changes in groundwater levels from 2010 with estimates reached ±23 meters, while the results of modeling at near surface (shallow groundwater level) indicate a groundwater level change of approximately ±8 meters from the year 2010.Keywords: microgravity, groundwater, modeling, hydrology, aquifer. ABSTRAKStudi terkait pemantauan airtanah dengan metode geofisika telah dilakukan sejak tahun 1990-an. Data gravity di permukaan dengan skema pengukuran gravimeter relatif dipilih pada pemantauan di area perkotaan karena cukup cepat, mudah, murah, dan relatif tidak merusak lingkungan. Signifikansi metode time-lapse microgravity pada target studi ini bergantung pada perubahan massa air pada lapisan akuifer di bawah permukaan. Area penelitian pada studi ini mencakup Kota Bandung dan beberapa area di sekitarnya dengan cakupan luasan interpolasi grid (18 x 17) km2. Perubahan gravitasi ditentukan oleh enam kali survei berulang pada beberapa titik pengamatan yang sama sejak 2010 sampai 2021. Tujuan dari penelitian ini adalah mengembangkan metode untuk mengestimasi perubahan muka airtanah berdasarkan pemodelan data time-lapse microgravity. Kompleksitas perubahan densitas di bawah permukaan disederhanakan untuk dua bagian terkait perubahan densitas dekat permukaan dan perubahan densitas pada lapisan akuifer menengah. Kecenderungan dari data muka airtanah pada tahun 2010 digunakan sebagai acuan untuk menentukan estimasi pada tahun 2015, 2016 (Februari dan Agustus), 2019, dan 2021. Hasil pemodelan pada akuifer menengah (sistem airtanah tertekan) memberikan perubahan muka airtanah dari tahun 2010 dengan estimasi mencapai ±23 meter, sedangkan hasil pemodelan pada kedalaman yang lebih dangkal (muka airtanah dangkal) menunjukkan perubahan muka airtanah mencapai ±8 meter dari tahun 2010.Kata Kunci: microgravity, airtanah, pemodelan, hidrologi, akuifer

Structure Evolution and Palinspastic Analysis of The Gurami-Tamiang Area, North Sumatra Basin, Indonesia Dumex Pasaribu; Benyamin Sapiie; Indra Gunawan
Scientific Contributions Oil and Gas Vol 48 No 3 (2025)
Publisher : Testing Center for Oil and Gas LEMIGAS

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.29017/scog.v48i3.1806

The Sumatran back-arc basins developed beginning in the Middle Eocene, characterized by a variety of graben alignment patterns, which serve as critical indicators in understanding their formation history. One such basin is the North Sumatra Basin, dominated by north-south-trending grabens. These grabens are best observed in the Gurami-Tamiang Area. This research focuses on the subsurface analysis of this area, specifically: (i) detailed seismic interpretation of four east-west cross-sections that span several grabens, and (ii) palinspastic reconstructions to investigate structural and strain evolution over time, and its tectonochronostratigraphic chart. Generally, the structural configuration of the Gurami-Tamiang Area is defined by half-grabens bounded by east-dipping faults originating from negative flower structures at depth. The results show three phases of evolution: (i) Extensional Phase (45 - 32 Ma) is characterized by growth strata and strain magnitudes of (+) 4.2% to (+) 11.64%, (ii) Transitional Phase (32 - 22 Ma) is displaying both positive and negative strains of (+) 2.3% to (-) 1.7%, with growth strata that are extending across grabens; and (iii) Contractional Phase (22 Ma – present) is characterized by negative strains of (-) 0.92% toward zero and mostly covered by post-extensional and syn-inversion deposits. The evolutionary phases indicate a novelty in the area, with the graben formation being part of a wrench fault system that includes the Khlong-Marui Fault, the Lokop-Kutacane Fault, and the Sumatra Fault.

Optimizing Gravity Forward Modeling through OpenMP Parallel Approach: A Case Study in Bawean Island Indra Gunawan; Susanti Alawiyah
Indonesian Journal on Computing (Indo-JC) Vol. 10 No. 1 (2025): August, 2025
Publisher : Telkom University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.21108/indojc.v10i1.9068

This study investigates the optimization of Gravity Forward Modeling (GFM) by implementing an OpenMP parallel computing approach, focusing on the synthetic model and topography of Bawean Island. The research addresses computational limitations in traditional GFM by utilizing parallel processing techniques to enhance efficiency and resolution. By modeling subterranean layers with rectangular prisms and using the Okabe equation for calculations, the study significantly improves computational speed and resource management. The practical application on Bawean Island includes a strategic distribution of observation stations to facilitate Bouguer Anomaly (BA) computations, providing a clearer understanding of subsurface density anomalies. Notably, the study demonstrates a 600% increase in efficiency for the synthetic case when OpenMP with 8 threads is applied to the utilized architecture. For the field model, computations spanning 400 square kilometers on Bawean Island, encompassing over 1.3 billion GFM calculations, are completed in just 143 seconds. Additionally, the gravity terrain values on Bawean Island exhibit a range of up to 65 mGal, which closely correlates with the high-resolution topographic map. These findings highlight the considerable advantages of parallel computing in enhancing the efficiency and feasibility of complex geophysical modeling tasks, offering substantial improvements for large-scale geophysical exploration.

Study on the Significance of Reduction to the Equator (RTE), Reduction to the Pole (RTP), and Pseudogravity in Magnetic Data Interpretation Mira Nailufar Rusman; Susanti Alawiyah; Indra Gunawan
Jurnal Penelitian Pendidikan IPA Vol 9 No 8 (2023): August
Publisher : Postgraduate, University of Mataram

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.29303/jppipa.v9i8.4705

Interpretation of geomagnetic anomaly data is challenging, due to the influence of the Earth's dipole magnetic field. In this study, we investigate the significance of employing methods to transform dipole anomalies into monopoles, aiming to enhance the interpretability of the data. Four methods were examined: Reduce to Pole (RTP), Reduce to Equator (RTE), and Pseudo-Gravity. The RTP method was implemented using general equations for RTP, Pseudo-inclination (PI), and Nonlinear thresholding (NTRTP). The computation programs for RTP and RTE were developed using the Matlab programming language. Synthetic models were constructed to investigate the effects of inclination values, object dimensions, and positions on the resulting magnetic anomaly response. The result shows that NTRTP methods give the best result with coefficient correlation >0.9. It can be used in every condition (low or high inclination). The implementation was conducted utilizing magnetic data in the Gunung Pandan geothermal area. The application of the reduced to the pole (RTP) technique on the field data successfully remove the dipole effects, and make interpretation process easier. Based on RTP map, the range of anomaly values spanning from -800 nT to 1000 nT. High anomalies were observed at the Gunung Pandan site, indicative of a probable intrusion of andesitic igneous rock.

ANALISIS SEKATAN SESAR PADA SEGMEN ZONA SESAR LEMATANG CEKUNGAN SUMATERA SELATAN: IMPLIKASI TERHADAP MIGRASI HIDROKARBON Shinta Ayu Puspita; Benyamin Sapiie; Indra Gunawan; Aveliansyah Aveliansyah
Jurnal Geosaintek Vol. 11 No. 3 (2025)
Publisher : Institut Teknologi Sepuluh Nopember

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12962/j25023659.v11i3.8985

Sesar Lematang merupakan salah satu struktur utama di Cekungan Sumatera Selatan yang berperan penting dalam mengontrol pola deformasi, sedimentasi, dan sistem petroleum. Sesar Lematang berfungsi sebagai batas morfotektonik aktif yang terbentuk sejak fase ekstensional Eosen–Oligosen dan mengalami reaktivasi pada fase kompresi Miosen–Plio-Plistosen. Penelitian ini bertujuan untuk mengidentifikasi kerangka struktur dan mengevaluasi kemampuan sekatan (fault sealing capacity) Sesar Lematang berdasarkan integrasi data seismik 2D, data sumur, dan analisis petrofisika. Metode yang digunakan meliputi interpretasi seismik struktural untuk menentukan bidang dan geometri sesar, analisis petrofisika untuk menghitung kandungan lempung (Vshale), serta perhitungan Shale Gouge Ratio (SGR) guna menilai kemampuan sekatan sesar. Hasil perhitungan menunjukkan nilai SGR berkisar antara 47–61% dengan rata-rata sekitar 54%. Kombinasi kedua parameter tersebut. Implikasi hasil penelitian ini menunjukkan bahwa segmen-segmen Sesar Lematang berpotensi membentuk perangkap bertipe fault-bounded dan perangkap kombinasi stratigrafi-struktural yang baik bagi akumulasi hidrokarbon. Oleh karena itu, pemahaman terhadap kerangkas struktur dan perilaku sekatan Sesar Lematang menjadi aspek penting dalam strategi eksplorasi dan pengembangan migas di Cekungan Sumatera Selatan

The Tectonic Control on Karstification in The Faumai Formation, Bird’s Head, West Papua, Indonesia Marlon Nauw; Benyamin Sapiie; Indra Gunawan; Dwiharso Nugroho
Scientific Contributions Oil and Gas Vol 49 No 2 (2026)
Publisher : Testing Center for Oil and Gas LEMIGAS

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.29017/scog.v49i2.2076

This study investigates tectonic control on karstification within Eocene Faumai Formation in Bird’s Head region, West Papua, Indonesia. An integrated workflow was applied using surface outcrop observations, drilling indicators (including total mud losses, weight on bit, standpipe pressure, and equivalent circulating density), drilling events, and 3D seismic data from Tangguh area. The aim was to identify the distribution of karstified intervals, evaluate role of structural deformation, and reconstruct tectono-stratigraphic evolution associated with karst development.Faumai Formation is subdivided into four sequences, with karst development most pronounced in Faumai-2 interval. Evidence of karstification includes cave occurrences in outcrops, significant drilling mud losses, and low-impedance or trough reflectivity to chaotic seismic anomalies interpreted as subsurface cavities and collapse-related features concentrated along fault-controlled zones.The results indicate that oblique convergence among Australian, Caroline, and Pacific plates drove Late Oligocene uplift, exposing carbonate units to subaerial conditions and enabling meteoric dissolution along structural highs, fractures, and fault networks. Grain-supported dolomitic textures in the Faumai-2 interval suggest more favorable rock properties for karst development than in other sequences. Younger tectonic reactivation during Pleistocene subsequently produced collapse features recognized in both seismic and outcrop data, indicating that karstification in Faumai Formation is a multi-phase process controlled by both tectonics and carbonate facies architecture.

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