scholarly journals Geothermal Reservoir Identification based on Gravity Data Analysis in Rajabasa Area- Lampung

2021 ◽  
Vol 31 (2) ◽  
pp. 77
Author(s):  
Muh Sarkowi ◽  
Rahmat Catur Wibowo
Keyword(s):  
Gradient Analysis ◽  
Hot Spring ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Ground Level ◽  
Geothermal System ◽  
Mountain Area ◽  
Density Values ◽  
Fault Structures ◽  
Reservoir Identification

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.

Overdeepenings modelled with gravimetry-based data

2020 ◽  
Author(s):  
Dimitri Bandou ◽  
Patrick Schläfli ◽  
Michael Schwenk ◽  
Guilhem Douillet ◽  
Edi Kissling ◽  
...  
Keyword(s):  
Earth Science ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Borehole Data ◽  
Regional Trend ◽  
Shallow Subsurface ◽  
Base Level ◽  
Geological Past ◽  
Central Switzerland ◽  
Density Values

<p>The processes and mechanisms resulting in overdeepenings, valleys carved deeper than today’s rivers base level during glaciations, are still a matter of debate. Whether or not these valleys formation is due to glacial or fluvio-glacial processes or through fluvial down cutting in the geological past is difficult to affirm, as the depressions are filled with sediment or host lakes (Cook and Swift, 2012). In order to bypass this limitation, we use precise gravimetric data, GNSS data and borehole data, which we combine within a 3D forward modelling code, Gravi3D. We particularly aim at reconstructing the geometry of overdeepened valleys’ walls, which bear information on the erosional mechanism leading to the formation of these troughs. We proceed through the building of models for a given geometry to reproduce the Bouguer gravity that we measured in the field along sections and on a grid of stations. We constrain our models by using precise density values, determined by gravimetry, along with borehole data.</p><p>We apply this technique to overdeepenings located in the Alpine foreland (Belpberg area, Central Switzerland) because this area hosts multiple overdeepenings from the past glaciations. The region is characterized by three hill ranges made up of Molasse bedrock with c. 300 m-deep and c. 1 km-wide valleys in-between, where overdeepenings with a Quaternary infill are expected. The results of gravity data collection, accomplished over a section with stations spaced between 100 and 300 m and after standard corrections yield a Bouguer anomaly for the Belpberg region that ranges from c. -99 to -106 mgal. We infer this large range to the regional trend (c. 2 mgal over 8 km) and to the effect of the overdeepening infill (2-4 mgal over 1 km), disclosing a sharp anomaly pattern over the inferred overdeeping. The subsequent three steps include: (i) the removal of the regional trend, (ii) the use of the Nettleton method for the quantification of an accurate density contrast between the Molasse bedrock and the Quaternary infill, and (iii) the configuration of Gravi3D for the Belpberg situation, will yield further information on the morphology of the overdeeping. We thus conclude that Gravi3D, within this framework, is a useful tool to determine the geometry of overdeepings in particular, and shallow subsurface bodies and structures in general.</p><p>Reference:</p><p>Cook, S.J., Swift, D.A., 2012. Subglacial basins: Their origin and importance in glacial systems and landscapes. Earth-Science Reviews 115, 332–372.</p>

scholarly journals 2D Forward Modeling Geothermal System Gravity Data in South Solok Region, West Sumatra

2021 ◽  
Vol 4 (1) ◽  
pp. 36-44
Author(s):  
Muhammad Nafian ◽  
Belista Gunawan ◽  
Nanda Ridki Permana
Keyword(s):  
Heat Source ◽  
Geothermal Energy ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Filter Method ◽  
Geothermal System ◽  
Geothermal Systems ◽  
West Sumatra ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

Indonesia has the greatest potential for geothermal energy in the world. Geothermal has an important role as an alternative fuel because it is a renewable energy source, but its use has not been maximized. One of the areas that have the greatest potential for geothermal energy in South Solok, West Sumatra. Therefore, this study was conducted to determine the geothermal system in the South Solok area, West Sumatra by using the gravity method. The gravity data processing stage requires some software to get the CBA value(Complete Bouguer Anomaly), map contours of the CBA. Anomaly separation with the butterworth filter method, determination of residual anomaly slice points, and 2D modeling of geothermal systems. Based on modeling, the qualitative interpretation interprets the Complete Bouguer Anomaly map which is suspected as a geothermal prospect area is a low anomaly ranging from 7.9 mgal - 9.4 mgal which is marked in dark blue. Meanwhile, quantitative interpretation produces modeling of the AB and CD slicing with a total of four layers. This layer consists of clay rock as a cap rock, sandstone as a reservoir, granite as a heated rock as a heat source, and the last layer in the form of magma as a heat source. The anomaly modeling of these two sections is dominated by granite rock with a density value of 2500 kg/m3 for the AB section and 2550 kg/m3 for the CD section.

Bouguer density determination by fractal analysis

Geophysics ◽  
1990 ◽  
Vol 55 (7) ◽  
pp. 932-935 ◽  
Author(s):  
Freyr Thorarinsson ◽  
Stefan G. Magnusson
Keyword(s):  
Fractal Dimension ◽  
Fractal Analysis ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
New Method ◽  
Data Sets ◽  
Isostatic Compensation ◽  
Topographic Features ◽  
Density Determination ◽  
Density Values

Density values for the Bouguer reduction of two gravity data sets from Iceland are determined using a new method based on minimization of the roughness of the Bouguer anomaly surface. The fractal dimension of the surface is used as a gauge of the roughness. The analysis shows the size of topographic features supported by crust without isostatic compensation to be 25 to 30 km in southwest Iceland and 9 to 10 km inside the active rifting zone. The densities selected for these areas are 2490 and [Formula: see text], respectively.

scholarly journals Using highly accurate land gravity and 3D geologic modeling to discriminate potential geothermal areas: Application to the Upper Rhine Graben, France

Geophysics ◽  
2020 ◽  
Vol 85 (2) ◽  
pp. G35-G56
Author(s):  
Yassine Abdelfettah ◽  
Jacques Hinderer ◽  
Marta Calvo ◽  
Eléonore Dalmais ◽  
Vincent Maurer ◽  
...  
Keyword(s):  
Bulk Density ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Upper Rhine Graben ◽  
Borehole Data ◽  
Geothermal Potential ◽  
Density Values ◽  
Density Analysis ◽  
Gravity Interpretation ◽  
Upper Rhine

New land gravity data results acquired in northern Alsace were presented. Compared to the available old Bouguer anomaly, we recovered an accurate Bouguer anomaly field showing data uncertainties [Formula: see text]. A qualitative data analysis using pseudotomographies reveals several negative anomalies suggesting a decrease of the bulk density at the depth of geothermal interest. We have performed a quantitative study on the basis of the existing 3D geologic model derived from a reinterpretation of the vintage seismics. The theoretical gravity response indicates a great mismatch with the observed Bouguer anomaly. The stripping approach was applied, and the stripped Bouguer anomaly indicates that the density values of the Jurassic, but especially for the Triassic, the Buntsandstein, and the upper part of the basement, were overestimated even using the density values measured in the deep geothermal borehole. This suggests that the borehole density values do not reflect the density variations occurring at larger scale. To reduce the Bouguer anomaly during stripping, a negative density contrast should be affected to the Buntsandstein layer overlaying the basement, suggesting that the part located between the Buntsandstein and the upper part of the basement presents a low-density value compared to the reference density, which is not necessarily expected and is not observed in the densities measured in the borehole. Interestingly, a correlation is found between the gravity analyses and the thermal gradient boreholes in the northern part of the study area. For two boreholes, the gravity interpretation suggests a huge density decrease in the Buntsandstein, which may arise from a combination of high-density fracturing and the important quantity of geothermal fluid significantly affecting the bulk density. Analysis of the thermal borehole data suggests that these two boreholes indicate higher geothermal potential compared with the other boreholes.

scholarly journals THE INVESTIGATION OF KADIDIA GEOTHERMAL FIELD (INDONESIA) USING GRAVITATIONAL DATA AND POWER SPECTRUM ANALYSIS

2021 ◽  
Vol 84 (1) ◽  
pp. 149-157
Author(s):  
Sismanto Sismanto ◽  
Anis Hoerunisa ◽  
Dikdik Risdianto ◽  
Tony Rahadinata
Keyword(s):  
Power Spectrum ◽  
Spectrum Analysis ◽  
Gravity Data ◽  
Volcanic Rocks ◽  
Bouguer Anomaly ◽  
Secondary Data ◽  
Geothermal Field ◽  
Power Spectrum Analysis ◽  
Source Rocks ◽  
Geothermal System

Kadidia is one of the area with geothermal potential in Central Sulawesi, Indonesia. Therefore, this study aims to estimate the depth of reservoir and identify subsurface geological structures using gravity data and power spectrum analysis. It uses secondary data from the field survey results of the geophysical team from the Mineral and Geothermal Resource Center Agency. Furthermore, the data were processed to obtain a complete Bouguer anomaly, reduction in a flat field, regional and residual anomalies. The results of residual anomalies showed high and low values in the range of (5-13) mGal corresponding to volcanic rocks and in the range of -10 to -4 mGal spread evenly in the study area respectively. The analysis of derivative showed the presence of intrusive rocks which are thought to be granite, and the power spectrum showed that the heat source rocks from the geothermal system were inferred as granite at a depth of more than (3.68-6.00) km. In addition, the reservoir rocks were interpreted as low-density sandstones at a depth of (0.80-1.37) km, and a caprock in the form of sandstones with medium density at a depth of (0.20-0.80) km, and from the surface to 0.20 km is soil. The interpretation of three-dimensional modeling showed that the faults control geothermal manifestations, i.e. the Koalarawa and Towingkoloe faults, which extends from northwest-southeast.

scholarly journals Geometrical Characterisation of the Mamfe Basin, Cameroon, from the Earth, Gravitational Model (EGM 2008)

2018 ◽  
Vol 7 (1) ◽  
pp. 94
Author(s):  
Anatole Eugene Djieto Lordon ◽  
Mbohlieu YOSSA ◽  
Christopher M Agyingi ◽  
Yves Shandini ◽  
Thierry Stephane Kuisseu
Keyword(s):  
Average Length ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Igneous Rocks ◽  
Average Depth ◽  
The Earth ◽  
Gravitational Model ◽  
Petroleum Generation ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

Gravimetric studies using the ETOPO1-corrected high resolution satellite-based EGM2008 gravity data was used to define the surface extent, depth to basement and shape of the Mamfe basin. The Bouguer anomaly map was produced in Surfer 11.0. The Fast Fourier Transformed data was analyzed by spectral analysis to remove the effect of the regional bodies in the study area. The residual anomaly map obtained was compared with the known geology of the study area, and this showed that the gravity highs correspond to the metamorphic and igneous rocks while the gravity lows match with Cretaceous sediments. Three profiles were drawn on the residual anomaly map along which 2D models of the Mamfe basin were drawn. The modeling was completed in Grav2dc v2.06 software which uses the Talwini’s algorithm and the resulting models gave the depth to basement and the shape of the basement along the profiles. After processing and interpretation, it was deduced that the Mamfe basin has an average length and width of 77.6 km and 29.2 km respectively, an average depth to basement of 5 km and an overall U-shape basement. These dimensions (especially the depth) theoretically create the depth and temperature conditions for petroleum generation. 

scholarly journals Lineament Extraction using Gravity Data in the Citarum Watershed

2021 ◽  
Vol 53 (1) ◽  
Author(s):  
Gumilar Utamas Nugraha ◽  
Karit Lumban Goal ◽  
Lina Handayani ◽  
Rachmat Fajar Lubis
Keyword(s):  
Gravity Data ◽  
Bouguer Anomaly ◽  
High Density ◽  
Low Density ◽  
Residual Value ◽  
Satellite Gravity ◽  
Structural Weakness ◽  
Major Trend ◽  
Lineament Extraction ◽  
Butterworth Filters

Lineament is one of the most important features showing subsurface elements or structural weakness such as faults. This study aims to identify subsurface lineament patterns using automatic lineament in Citarum watershed with gravity data. Satellite gravity data were used to generate a sub-surface lineament. Satellite gravity data corrected using Bouguer and terrain correction to obtain a complete Bouguer anomaly value. Butterworth filters were used to separate regional and residual anomaly from the complete Bouguer anomaly value. Residual anomaly gravity data used to analyze sub-surface lineament. Lineament generated using Line module in PCI Geomatica to obtain sub-surface lineament from gravity residual value. The orientations of lineaments and fault lines were created by using rose diagrams. The main trends observed in the lineament map could be recognized in these diagrams, showing a strongly major trend in NW-SE, and the subdominant directions were in N-S. Area with a high density of lineament located at the Southern part of the study area. High-density lineament might be correlated with fractured volcanic rock upstream of the Citarum watershed, meanwhile, low-density lineament is associated with low-density sediment. The high-density fracture might be associated with intensive tectonics and volcanism.

3D Gravity modeling of the volcanic island of Surtsey, Iceland

2021 ◽  
Author(s):  
sara sayyadi ◽  
Magnús T. Gudmundsson ◽  
Thórdís Högnadóttir ◽  
James White ◽  
Joaquín M.C. Belart ◽  
...  
Keyword(s):  
Sea Level ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Gravity Modeling ◽  
Gravity Station ◽  
Effusive Activity ◽  
3D Gravity ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
Drill Cores

<p>The formation of the oceanic island Surtsey in the shallow ocean off the south coast of Iceland in 1963-1967 remains one of the best-studied examples of basaltic emergent volcanism to date. The island was built by both explosive, phreatomagmatic phases and by effusive activity forming lava shields covering parts of the explosively formed tuff cones.  Constraints on the subsurface structure of Surtsey achieved mainly based on the documented evolution during eruption and from drill cores in 1979 and in the ICDP-supported SUSTAIN drilling expedition in 2017(an inclined hole, directed 35° from the vertical). The 2017 drilling confirmed the existence of a diatreme, cut into the sedimentary pre-eruption seafloor (Jackson et al., 2019). </p><p>We use 3D-gravity modeling, constrained by the stratigraphy from the drillholes to study the structure of the island and the underlying diatreme.  Detailed gravity data were obtained on Surtsey in July 2014 with a gravity station spacing of ~100 m. Density measurements for the seafloor sedimentary and tephra samples of the surface were carried out using the ASTM1 protocol. By comparing the results with specific gravity measurements of cores from drillhole in 2017, a density contrast of about 200 kg m<sup>-3</sup> was found between the lapilli tuffs of the diatreme and the seafloor sediments.  Our approach is to divide the island into four main units of distinct density: (1) tuffs above sea level, (2) tuffs below sea level, (3) lavas above sea level, and (4) a lava delta below sea level, composed of breccias over which the lava advanced during the effusive eruption.  The boundaries between the bodies are defined from the eruption history and mapping done during the eruption, aided by the drill cores. </p><p>A complete Bouguer anomaly map is obtained by calculating a total terrain correction by applying the Nagy formula to dense DEMs (5 m spacing out to 1.2 km from station, 200 m spacing between 1.2 km and 50 km) of both island topography and ocean bathymetry.  Through the application of both forward and inverse modeling, using the GM-SYS 3D software, the results provide a 3-D model of the island itself, as well as constraints on diatreme shape and depth.</p>

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