scholarly journals Geothermal Reservoir Identification in Way Ratai Area Based on Gravity Data Analysis

2021 ◽  
Vol 2110 (1) ◽  
pp. 012004
Author(s):  
M Sarkowi ◽  
R C Wibowo ◽  
Karyanto
Keyword(s):  
Density Distribution ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Geothermal Reservoir ◽  
Gravity Gradient ◽  
Low Density ◽  
3D Inversion ◽  
Magnetotelluric Data ◽  
Fault Structure ◽  
Geothermal Reservoirs

Abstract Gravity research in the Way Ratai geothermal prospect area was conducted to determine geothermal reservoirs, heat sources, and the structure of the geothermal reservoir. The research carried out includes 3D inversion modeling of gravity data. The Bouguer anomaly in the study area has 50 mGal to 120 mGal with low anomalies located in the southeast (Ketang and Kelagian), Northeast (Gedong Air, Sungai Langka, Gunung Betung) areas, and in the Pesawaran mountain area. The high anomaly is in Merawan – Hanuberak – Padang Cermin, Sumbersari and Kaliawi. The horizontal gravity gradient map analysis shows a pattern of fault structure trending northwest-southeast and southwest-northeast, according to the main fault structure in the area. 3D inversion modeling obtains a density distribution between 1.8 g/cc to 3g/cc with a low-density distribution in the south, Mount Pesawaran/Ratai, Gunung Betung, and Sidoharum. The location of the manifestation is 9 km southeast of the Mount Ratai/Pesawaran summit. The existence of geothermal reservoirs is estimated to be in the Lubuk Badak and Miwung Hills areas which are located between the peaks of Mount Ratai/Pesawaran and geothermal manifestations. This is supported by the low-density distribution in the area and the resistivity map from audio-magnetotelluric data.

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.

Constructing piecewise-constant models in multidimensional minimum-structure inversions

Geophysics ◽  
2008 ◽  
Vol 73 (1) ◽  
pp. K1-K9 ◽  
Author(s):  
Colin G. Farquharson
Keyword(s):  
Gravity Data ◽  
Model Structure ◽  
Iteratively Reweighted Least Squares ◽  
3D Inversion ◽  
Magnetotelluric Data ◽  
2D Inversion ◽  
Piecewise Constant ◽  
Text Type ◽  
Current Minimum ◽  
Modified Algorithm

A modification of the typical minimum-structure inver-sion algorithm is presented that generates blocky, piecewise-constant earth models. Such models are often more consistent with our real or perceived knowledge of the subsurface than the fuzzy, smeared-out models produced by current minimum-structure inversions. The modified algorithm uses [Formula: see text]-type measures in the measure of model structure instead of the traditional sum-of-squares, or [Formula: see text], measure. An iteratively reweighted least-squares procedure is used to deal with the nonlinearity introduced by the non-[Formula: see text] measure. Also, and of note here, diagonal finite differences are included in the measure of model structure. This enables dipping interfaces to be formed. The modified algorithm retains the benefits of the minimum-structure style of inversion — namely, reliability, robustness, and minimal artifacts in the constructed model. Two examples are given: the 2D inversion of synthetic magnetotelluric data and the 3D inversion of gravity data from the Ovoid deposit, Voisey’s Bay, Labrador.

A new look at Belgian aeromagnetic and gravity data through image-based display and integrated modelling techniques

1993 ◽  
Vol 130 (5) ◽  
pp. 583-591 ◽  
Author(s):  
B. C. Chacksfield ◽  
W. De Vos ◽  
L. D'Hooge ◽  
M. Dusar ◽  
M. K. Lee ◽  
...  
Keyword(s):  
Large Scale ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Digital Processing ◽  
Integrated Modelling ◽  
Magnetic Data ◽  
Gravity Gradient ◽  
The North ◽  
Anomaly Map ◽  
Shaded Relief

AbstractDigital processing and image-based display techniques have been used to generate contour and shaded-relief maps of Belgian aeromagnetic data at a scale of 1:300000 for the whole of Belgium. These highlight the important anomalies and structural trends, particularly over the Brabant Massif. North and vertically illuminated shaded-relief plots, enhanced structural belts trending west–east to northwest–southeast in the Brabant Massif and west–east to southwest–northeast in the core of the Ardennes. The principal magnetic lineaments have been identified from the shaded-relief plots and tentatively correlated to basement structures. Most short lineaments are correlated with individual folds while the more extensive lineaments are correlated with large scale fault structures. Magnetic highs within the Brabant Massif are attributed to folded sediments of the Tubize Group. The magnetic basement in the east of Belgium is sinistrally displaced to the north by an inferred deep NNW–SSE crustal fracture. The Bouguer anomaly map of Belgium identifies the Ardennes as a negative area, and the Brabant Massif as a positive area, with the exception of a WNW–trending gravity low in its western part. The southern margin of the Brabant Massif is defined by a steep gravity gradient coincident with the Faille Bordiere (Border Fault). Trial modelling of the gravity and magnetic data, carried out along profiles across the Brabant and Stavelot massifs, has identified probable acid igneous intrusions in the western part of the Brabant Massif, and a deep magnetic lower density body underlying the whole Ardennes region, which is thought to be a distinctive Precambrian crustal block.

Geometry of alpine overdeepenings assessed with gravimetry and 3-D modelling

2021 ◽  
Author(s):  
Dimitri Bandou ◽  
Patrick Schläfli ◽  
Michael Schwenk ◽  
Guilhem A. Douillet ◽  
Edi Kissling ◽  
...  
Keyword(s):  
Gravity Data ◽  
Bouguer Anomaly ◽  
Satellite System ◽  
Gravity Gradient ◽  
Gravitational Attraction ◽  
Borehole Data ◽  
Regional Trend ◽  
Study Region ◽  
The North ◽  
Modelling Framework

<p>Interpretations of the processes leading to the formation of overdeepened valleys, where the bedrock lies well below sea level today, are contested as the overdeepenings have been filled by sediments or host lakes making observations difficult. Here, we combine gravimetric, GNSS (Global Navigation Satellite System) and borehole data within a 3D forward modelling framework (Gravi3D) to assess the 3-D subsurface geometry of such overdeepenings in the Swiss plateau, to the North of the Alps. Gravi3D has two components (PRISMA and BGPoly), which allow to obtain analytically the gravity effect of prisms and polygons (Nagy (1966) and Talwani & Ewing (1960)). PRISMA allows first to estimate the spatial extent of an overdeepening and the density contrast between the overdeepening fill and the bedrock. In contrast, BGPoly is designed to disclose the details of a complex 3-D geometry of an overdeepening fill through an approximation of its shape with polygons. Gravi3D will be open access and is designed for a larger scientific community.</p><p> <br>Here, we focus on overdeepenings beneath two valleys, the Aare valley and the Gürbe valley to the South of Bern. In this region, the occurrence of overdeepenings has already been disclosed through drilling, but the details about the geometry have not been elaborated yet. The study region is characterized by three mountain ranges oriented North-South and comprises Burdigalian Upper Marine Molasse bedrock. The Gürbe and Aare valleys in-between are c. 300 m-deep and c. 1 km-wide, where overdeepenings with a >100 m-thick Quaternary fill have already been identified by drilling. The gravity data collected along an 8 km-long profile with stations spaced between 100 and 300 m yield a Bouguer anomaly that ranges from c. -99 to -106 mGal. We relate this anomaly to the regional trend (c. 2 mGal over 8 km) and to the effect of the overdeepenings’ sedimentary fillings (2 – 4 mGal/km), disclosing a sharp anomaly pattern over the inferred tunnel valleys. The removal of the signal related to the regional trend results in a residual anomaly of c. 1 mGal for the bedrock ridge in-between the valleys (Belpberg mountain), and of -2.65 and -3.56 mGal for the Gürbe and Aare valley overdeepenings, respectively. We observe a steeper gravity gradient for the Eastern flank of both overdeepenings. The use of Nettleton method to model the residual gravity anomaly across Belpberg yields a density of 2.5 g/cm<sup>3</sup> for the Molasse bedrock. In addition, the estimation of the largest gravity response through the overdeepening fill, calculated with Prisma yields a density value of c. 2.0 – 2.2 g/cm3 for the Quaternary sediments. As a further information, Prisma predicts a maximum thickness of 140 m for the Quaternary suite beneath the Gürbe valley and at least 200 m beneath the Aare valley. This yields a minimum slope of approximately 18° for the Gürbe overdeepening.</p><p> </p><p>REFERENCES</p><p>Nagy, D.: The gravitational attraction of a right rectangular prism. Geophysics 31, 362–371, 1966.</p><p>Talwani, M., Ewing, M.: Rapid computation of gravitational attraction of three‐dimensional bodies of arbitrary shape. Geophysics 25, 203–225, 1960.</p>

Geophysical characterization of the Menengai volcano, Central Kenya Rift from the analysis of magnetotelluric and gravity data

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. B187-B199 ◽  
Author(s):  
Antony Munika Wamalwa ◽  
Kevin L. Mickus ◽  
Laura F. Serpa
Keyword(s):  
Gravity Data ◽  
Gravity Models ◽  
High Resistivity ◽  
Geothermal System ◽  
Low Density ◽  
Fracture Density ◽  
Density Region ◽  
Magnetotelluric Data ◽  
Low Resistivity ◽  
2D Resistivity

In this study, we qualitatively analyze detailed gravity and broadband magnetotelluric data in and surrounding the Menengai volcano of the East African rift in Kenya to assess geothermal potential of the region. Three-dimensional gravity models obtained by inverting residual gravity anomalies and 2D resistivity models obtained by inverting the transverse electric and transverse magnetic magnetotelluric modes show several common features. Our models show that a low-resistivity zone above a higher resistivity zone correlates with a low-density region located 1–4 km beneath the volcano. These zones may be related to a high temperature gradient or hydrothermally altered, fractured rocks. Additionally, a low-resistivity ([Formula: see text]) and a low-density region located approximately 4–6 km below the volcano may be related to molten material that is the source of heat for the geothermal system. The low-resistivity ([Formula: see text]) regions that correlated with a denser ([Formula: see text]) region within the caldera are bounded by high-resistivity ([Formula: see text]), high-density ([Formula: see text]) volcanic units implying that the dense and electrically resistive volcanic material is relatively cool and lacks significant fluid content that can lower resistivity. At shallow depths, 0.5–1.5 km below the caldera, a low-resistivity and low-to-moderate density region is interpreted as a zone with high fracture density that consists of clay minerals resulting from hydrothermal alteration. These results agree well with the results from previous seismic studies on the depth of the suggested molten rocks.

A least‐squares derivatives analysis of gravity anomalies due to faulted thin slabs

Geophysics ◽  
2003 ◽  
Vol 68 (2) ◽  
pp. 535-543 ◽  
Author(s):  
El‐Sayed M. Abdelrahman ◽  
Hesham M. El‐Araby ◽  
Tarek M. El‐Araby ◽  
Eid Ragab Abo‐Ezz
Keyword(s):  
Least Squares ◽  
Least Squares Method ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Theoretical Data ◽  
Gravity Anomalies ◽  
Random Errors ◽  
Fault Structure ◽  
Amplitude Coefficient ◽  
Buried Fault

This paper presents two different least‐squares approaches for determining the depth and amplitude coefficient (related to the density contrast and the thickness of a buried faulted thin slab from numerical first‐, second‐, third‐, and fourth‐horizontal derivative anomalies obtained from 2D gravity data using filters of successive graticule spacings. The problem of depth determination has been transformed into the problem of finding a solution to a nonlinear equation of the form f(z) = 0. Knowing the depth and applying the least‐squares method, the amplitude coefficient is determined using a simple linear equation. In this way, the depth and amplitude coefficient are determined individually from all observed gravity data. The depths and the amplitude coefficients obtained from the first‐, second‐, third‐, and fourth‐ derivative anomaly values can be used to determine simultaneously the actual depth and amplitude coefficient of the buried fault structure and the optimum order of the regional gravity field along the profile. The method can be applied not only to residuals but also to the Bouguer anomaly profile consisting of the combined effect of a residual component due to a purely local fault structure (shallow or deep) and a regional component represented by a polynomial of any order. The method is applied to theoretical data with and without random errors and is tested on a field example from Egypt.

scholarly journals IDENTIFIKASI BAWAH PERMUKAAN LAPANGAN MINYAK“HUF” SUMATERA SELATAN UNTUK MENDELINIASI STRUKTUR CEKUNGAN HIDROKARBON BERDASARKAN DATA GAYABERAT

2020 ◽  
Vol 4 (1) ◽  
pp. 19-32
Author(s):  
Ade Setiawan ◽  
Bagus Sapto Mulyatno
Keyword(s):  
3D Modeling ◽  
3D Model ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Hollow Structure ◽  
Field Research ◽  
Oil Field ◽  
Fault Structure ◽  
Vertical Derivative ◽  
A Value

Oil field research in regional Banyuasin “HUF” , South Sumatra have been done by the gravity data with objective of knowing fault structure based on analysis of hydrocarbon SVD and knows hollow structure  based on the 3D model of the Bouguer Anomaly and Residual Anomaly. Study areas had Bouguer Anomaly between 13 mgal up to 33 mgal to the interval 1 mgal, where the value of Bouguer Anomaly high have a range value 26 mgal up to 33 mgal which is in the direction of west. While the low value of Bouguer Anomaly have a range value 13 mgal to 20 mgal that is in the east. To knew the existence of structure fault, filtering Second Vertical Derivative (SVD) on a Bouguer Anomaly, Regional and Residua mapl.Pattern of structure fault indicated the contours of a zero value and between the high and low contours. From the results of the analysis SVD Complete Bouguer Anomaly and SVD Residual Anomaly there were 4 (four) fault, while from SVD Regional Anomaly there are 3 (three) fault. 3D modeling the Residual Anomaly were conducted to prove the existence of the fault SVD analyzed based on the results of the analysis and to know the hydrocarbon basin. Based on the results of the inversion of 3D the Residual Anomaly, basin was found in the depth of 1500 m – 3000 m with a value of the density ranges from 2.24 gram/cc until 2.32 gram/cc which identified as sandstone basin.

scholarly journals PEMODELAN DAN ANALISA STRUKTUR BAWAH PERMUKAAN DAERAH PROSPEK PANASBUMI KEPAHIANG BERDASARKAN METODE GAYABERAT

2020 ◽  
Vol 4 (2) ◽  
pp. 47-61
Author(s):  
Roy Bryanson Sihombing ◽  
Rustadi Rustadi
Keyword(s):  
Gravity Data ◽  
Bouguer Anomaly ◽  
Research Area ◽  
Inverse Modelling ◽  
3D Inversion ◽  
Vertical Derivative ◽  
The North ◽  
A Value ◽  
Value Range ◽  
Range Of Values

Research has been conducted in Kepahiang area using gravity data with the aim of identify faults based on analysis of the Second Vertical Derivative (SVD) and interpreting structure sub-surface of the based on 3D inverse modelling from Bouguer anomaly and residual anomaly. The research area have an Bouguer anomaly between 38 mGal - 74 mGal, where the high Bouguer anomaly value has a value range of 63,2 mGal - 74 mGal located in the southwest direction of the research area. Whereas the low Bouguer anomaly value has a range of values 38 mGal - 47 mGal located in the north of the research area. To know the existence of fault structure in research area, conducted filtering Second Vertical Derivative (SVD) on the map Bouguer anomaly, regional and residual. The structure faulting is shown with contour of zero and between the contours of high and low. From the analysis of SVD complete anomaly Bouguer and SVD residual anomaly there are 8 (eight) faulting, while from SVD regional anomaly there are 4 (four) fault. 3D inversion modeling of the residual anomaly was done to prove the existence of the fault analyzed based on filtering Second Vertical Derivative (SVD). Based on the results of inversion 3D residual anomaly been gained one (1) reservoir in a northern direction research area and two (2) in the direction of west the research area by a contrast the density of -0,0719356 gr/cc until -0,236053 gr/cc with a depth of 0 meters up to 4.705 meters.

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