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All Journal Journal of Mathematical and Fundamental Sciences Jurnal Geofisika
Darharta Dahrin
Applied Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung
Astronomy Chemistry Earth & Planetary Sciences Energy Mathematics Physics

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Constrained Two-Dimensional Inversion of Gravity Data Hendra Grandis; Darharta Dahrin
Journal of Mathematical and Fundamental Sciences Vol. 46 No. 1 (2014)
Publisher : Institute for Research and Community Services (LPPM) ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.math.fund.sci.2014.46.1.1

Abstract

The non-uniqueness in the solution of gravity inversion poses a major problem in the interpretation of gravity data. To overcome this ambiguity, "a priori" information is introduced by minimizing a functional that describes the geometrical or physical properties of the solution. This paper presents a 2D gravity inversion technique incorporating axes of anomalous mass concentration as constraints. The inverse problem is formulated as a minimization of the moment of inertia of the causative body with respect to the axes of the mass concentration. The proposed method is particularly applicable to homogeneous, linear mass distributions, such as mineralization along faults and intruded sills or dikes. Inversions of synthetic and field data illustrate the versatility of the implemented algorithm.
Full Tensor Gradient of Simulated Gravity Data for Prospect Scale Delineation Hendra Grandis; Darharta Dahrin
Journal of Mathematical and Fundamental Sciences Vol. 46 No. 2 (2014)
Publisher : Institute for Research and Community Services (LPPM) ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.math.fund.sci.2014.46.2.1

Abstract

Gravity gradiometry measurement allows imaging of anomalous sources in more detail than conventional gravity data. The availability of this new technique is limited to airborne gravity surveys using very specific instrumentation. In principle, the gravity gradients can be calculated from the vertical component of the gravity commonly measured in a ground-based gravity survey. We present a calculation of the full tensor gradient (FTG) of the gravity employing the Fourier transformation. The calculation was applied to synthetic data associated with a simple block model and also with a more realistic model. The latter corresponds to a 3D model in which a thin coal layer is embedded in a sedimentary environment. Our results show the utility of the FTG of the gravity for prospect scale delineation.
Pemodelan Penyebaran Massa CO2 Terinjeksi dalam reservoir untuk Mendapatkan Respon Anomali Time-lapse microgravity di Permukaan Dinda Rahmani; Darharta Dahrin
Jurnal Geofisika Vol 15 No 2 (2017): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v15i2.408

Abstract

Dalam proyek CCS, monitoring bawah permukaan perlu dilakukan dengan baik agar CO2 yang diinjeksikan dapat tersimpandengan aman di dalam reservoir. Salah satu metode geofisika yang dapat digunakan untuk monitoring bawah permukaan adalah metode gravity. Dengan membuat model sintetik volume reservoir, tekanan dan temperatur bawah permukaan, serta perhitungan aliran fluida pada rentang waktu tertentu, dapat diprediksi radius penyebaran CO2 dan distribusi densitasnya di dalam reservoir. Radius penyebaran dan kontras densitas yang didapatkan, digunakan untuk pemodelan ke depan time-lapse microgravity dengan menggunakan software MATLAB versi R2012a yang telah divalidasi dengan software yang sudah ada sebelumnya, GRAV3D versi 2.0. Berdasarkan perhitungan dan pemodelan yang telah dilakukan, diketahui peningkatan tekanan bottomhole mengakibatkan perubahan sifat fisis CO2 yang mempengaruhi radius penyebarannya. Kemudian, respon anomali time-lapse microgravity yang dihasilkan menunjukkan kecenderungan nilai anomali yang terus meningkat seiring bertambahnya massa CO2 yang diinjeksikan. Nilai anomali setengah maksimum dan radius yang didapatkan pada hari ke 720, yaitu 1,323 x 10-1µGal dan 631,688 m untuk penyebaran massa CO2 di dalam reservoir sejauh 96,436 m. Dari kurva perbandingan tekanan reservoir terhadap tekanan fracture dan litostatik pada hari ke 720, didapatkan nilai tekanan pada kedalaman reservoir yang diinjeksikan CO2 masih jauh di bawah tekanan fracture dan litostatik, sehingga penambahan massa dari injeksi CO2 yang dimodelkan ini sangat kecil berpotensi untuk menimbulkan rekahan baru pada formasi. Dengan demikian, hasil pemodelan penyebaran CO2 dan distribusi densitasnya dalam reservoir, yang dikaitkan pula dengan perbandingan tekanan reservoir terhadap tekanan fracture dan litostatik, dapat digunakan untuk menentukan aman atau tidaknya injeksi CO2 yang dimodelkan.
Analysis And Modelling Of Geoelectric Data Modeling For The Identication Of Groundwater aquifer At Cisarua Area, West Bandung A Daniswara; Darharta Dahrin; Setianingsih Setianingsih
Jurnal Geofisika Vol 17 No 2 (2019): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v17i2.416

Abstract

Groundwater is the main need of society in everyday life. Groundwater is one of renewable resources but it doesn’t mean that it can be exploitated without limit. Several factors that affect the availability of groundwater derived from nature such as geological conditions, rainfall, and green areas should be considered. Water in the soil is stored in a porous layer and has a good permeability is called an aquifer. Cisarua area is located in West Bandung regency, West Java which is a hilly area that has a topography with a slope ranging from normal to steep. The land use in this area is still dominated with plantation and forest as green area. Groundwater aquifer characteristics in that area needs to be examined and analysed for the needs of the community and agricultural business. In this research, the writer used inversion modeling technique of geoelectric data to visualize the condition of subsurface. Resistivity inversion modelling of apparent resistivity data as a result of resistivity method with Wenner-Schlumberger configuration is then carried out with least-square method. The initial model is modified in an iterative manner such that the sum of square error of the difference between the model response and the observed data values is minimized. The result of resistivity modelling is used for analysis of aquifer characteristic such as lithology, depth and structure along with considering geological reference. As the result of modelling, the area of measurement is divided into three zones which are Zone of aeration, Zone of Saturation, and endapan formasi. Zone of aeration is located at depth 0-25 m with resistivity 20-100 Ohm.m and the predicted lithology is gravel or weathered soil. Zone of Saturation (akuifer) is located at depth 25-60 m with resistivity 4-30 Ohm.m and the predicted lithology is sandstone or clay. Endapan Formasi Cibereum is located at more than 60 m from ground with resistivity more than 100 Ohm.m and the predicted lithology is sandy tuff or dry breccia.
Co-Authors A Daniswara Dinda Rahmani Hendra Grandis Setianingsih Setianingsih