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All Journal Journal of Engineering and Technological Sciences JURNAL SUMBER DAYA AIR Jurnal Geofisika
Eko Januari Wahyudi
Applied Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung
Civil Engineering, Building, Construction & Architecture Earth & Planetary Sciences Energy Engineering Physics

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Designing a Genetic Algorithm for Efficient Calculation in Time-Lapse Gravity Inversion Wahyudi, Eko Januari; Santoso, Djoko; Kadir, Wawan Gunawan Abdul; Alawiyah, Susanti
Journal of Engineering and Technological Sciences Vol 46, No 1 (2014)
Publisher : ITB Journal Publisher, LPPM ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (595.019 KB) | DOI: 10.5614/j.eng.technol.sci.2014.46.1.4

Abstract

As an advanced application of soft computation in the oil and gas industry, genetic algorithms (GA) can contribute to geophysical inversion problems in order to achieve better results and efficiency in the computational process. Time-lapse gravity responses to pore-fluid density changes can be modeled to provide the density distribution in the subsurface. This paper discusses the progress of work in inverse modeling of time-lapse gravity data using value encoding with alphabet formulation. The alphabet formulation was designed to provide the solution for positive and negative density change with respect to a reference value (0 gr/cc). The inversion was computed using a genetic algorithm as the optimization method. Working with genetic algorithms, time-intensive computational processes are a challenge, so the algorithm was designed in steps through the evaluation of a GA operator performance test. The performances of several combinations of GA operators (selection, crossover, mutation, and replacement) were tested with a synthetic model of a single-layer reservoir. Sharp boundaries of density changes in the reservoir layer were derived from interpretation of the averaged calculation of several model samples. Analysis showed that the combination of stochastic universal sample–multipoint crossover–quenched simulated annealing per generation–no duplicity achieved the most promising results.
Study of Calculation of Terrain Correction Using square pattern and sloped triangle Method in Karangsambung Area Salam, Rafi; Wahyudi, Eko Januari; Alawiyah, Susanti
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.v17i2.412

Abstract

Conventional assessments of terrain correction are carried out by laying out transparent paper containing the Hammer chart on topographic maps, then estimating the elevation for each compartment. But this procedure has disadvantages, the number of compartments are too small for area with many topographic variations, and there is a subjectivity from the observer in estimating the compartments height. This research aim to overcome these problems and get more accurate terrain correction value. In this research, estimation of terrain correction carried out using square pattern and sloped triangle method. This method divides the area around the measurement point into a zone containing a square-shaped and triangle compartment. The research start with testing the program by using synthetic data to see the effect of rock bodies on terrain correction value. Then the program was applied to Karangsambung to see the topographic influence around Karangsambung on terrain correction. The program is then applied to gravity data, and the results are compared with calculations using the Hammer chart. Based on the synthetic data test, it was found that the value of terrain correction from a rock body measuring 10 x 10 km with a height difference of 1000 m from the station no longer significantly affects at the distance of 20 km. The topography around Karangsambung in the form of South Seraju Ranges with altitude of 1000 m at distance of 20 30 km gives effect of 0.05 mGal on terrain correction, while the Quaternary Volcano with an altitude of 3000 m at distance of 30 40 km gives effect of 0.1 mGal. The results of applying program at the gravity data show that the use of the square pattern method is able to correct errors from Hammer chart up to 3 mGal. The difference between the calculation of the two methods is getting bigger in the station located at slope area. It happens because estimation of the height difference in slope area is more difficult to do.
PEMODELAN TIME-LAPSE MICROGRAVITY UNTUK ESTIMASI PERUBAHAN MUKA AIRTANAH DI BANDUNG, JAWA BARAT Wahyudi, Eko Januari; A. Kadir, Wawan Gunawan; Alawiyah, Susanti; Setianingsih, Setianingsih; Gunawan, Indra; Abdurrahman, Dadi
JURNAL SUMBER DAYA AIR Vol 19, No 2 (2023)
Publisher : Direktorat 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.  
Co-Authors Abdurrahman, Dadi Djoko Santoso Indra Gunawan Salam, Rafi Setianingsih Setianingsih, Setianingsih Susanti Alawiyah Susanti Alawiyah Wawan Gunawan A. Kadir Wawan Gunawan Abdul Kadir