Combination of Terrestrial and Satellite Gravity Data for the Characterization of the Southwestern Coastal Region of Cameroon: Appraisal for Hydrocarbon Exploration

The southwestern coastal region of Cameroon is an area of interest because of its hydrocarbon potential (gas and oil). Terrestrial and satellite gravity data were combined and analyzed to provide a better precision in determining the structure of the study area. Firstly, the two gravity databases (in situ and satellite) have been coupled and validated using the least square collocation technique. Then, spectral analysis was applied to the combined Bouguer anomaly map to evaluate the thickness of sediments in some localities. We found that the sedimentary cover of the southwestern coastal region of Cameroon has a thickness that varies laterally from 1.68 ± 0.08 to 2.95 ± 0.15 km , especially in the western part. This result confirms that our target area is a potential site for hydrocarbon exploration. The horizontal gradient method coupled with the upward continuation at variable heights has been used to highlight several lineaments and their directions (N-S, E-W, SW-NE, and SSW-NNE). Lineaments trending in an N-S orientation are predominant. The Euler deconvolution method was also applied to the Bouguer anomaly map to determine the position, orientation, and depth of the different superficial faults of the study area. It appears that the majority of superficial faults have an N-S and SSW-NNE orientation. These directions are correlated with those previously highlighted by the maxima of horizontal gradient. The structural map could be used for a better identification of the direction of fluid flow within the subsurface or to update the geological map of our study area.

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

Earth Science Research ◽

10.5539/esr.v7n1p94 ◽

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.

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

10.5194/egusphere-egu21-15769 ◽

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

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. &#160;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&#176; from the vertical). The 2017 drilling confirmed the existence of a diatreme, cut into the sedimentary pre-eruption seafloor (Jackson et al., 2019).&#160;We use 3D-gravity modeling, constrained by the stratigraphy from the drillholes to study the structure of the island and the underlying diatreme. &#160;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-3 was found between the lapilli tuffs of the diatreme and the seafloor sediments.&#160; 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.&#160; The boundaries between the bodies are defined from the eruption history and mapping done during the eruption, aided by the drill cores.&#160;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.&#160; 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.

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SHEAR ZONES IN NORTH EGYPT INTERPRETED FROM GRAVITY DATA

Geophysics ◽

10.1190/1.1440785 ◽

1977 ◽

Vol 42 (6) ◽

pp. 1207-1214 ◽

Cited By ~ 24

Author(s):

S. Riad

Keyword(s):

Gravity Data ◽

Bouguer Anomaly ◽

Shear Zones ◽

Gulf Of Suez ◽

Eastern Side ◽

Fault Systems ◽

Anomaly Map ◽

Bouguer Anomaly Map ◽

Transcurrent Faults

The Bouguer anomaly map for the northern part of Egypt was used for determining fault systems which are probably present in the area. These systems show the presence of a number of almost parallel shear zones, striking in a northwest‐southeast direction. Extrapolation of some of these zones is suggested in the Gulf of Suez area. The movement of the eastern side of each zone is thought to be right‐lateral to the southeast. The shear zones are probably related to the interaction between the European and African plates. They probably started developing in the Oligocene and are presently still active. The opening of the Gulf of Suez is thought to be mainly due to the action of these transcurrent faults.

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Processing steps for the compiling AAGRG gravity maps

10.5194/egusphere-egu2020-16484 ◽

2020 ◽

Author(s):

Pavol Zahorec ◽

Juraj Papčo ◽

Roman Pašteka ◽

Keyword(s):

Gravity Data ◽

Atmospheric Correction ◽

Bouguer Anomaly ◽

Taylor Series Expansion ◽

Methodological Innovation ◽

Atmospheric Effect ◽

Free Air ◽

Point Data ◽

Anomaly Map ◽

Bouguer Anomaly Map

First unified complete Bouguer anomaly map of AlpArray area compiled from terrestrial gravity data is in preparation. The following steps to calculate the first version of the map were performed: 1. unification of different spatial, height and gravity systems, 2. getting available detailed (mainly LiDAR-based) elevation models and their transformation from physical to ellipsoidal heights, 3. calculation of mass corrections (gravity effect of the topography between the surface and ellipsoid level) with density 2 670 kg/m3, 4. calculation of bathymetric corrections for water masses below the ellipsoid (correction density -1&#160;640 kg/m3), 5. calculation of lake correction for great alpine lakes (correction density -1&#160;670 kg/m3), 6. calculation of the final complete Bouguer anomalies based on normal field (Somigliana formula with GRS80 parameters, free-air correction using Taylor series expansion to the 2nd order) and particular corrections including also the atmospheric correction.The quality control of input data was performed based on the height differences between the point data and particular elevation models. Several thousand points with height residuals higher than chosen threshold (&#177;50 m) were excluded. The available detailed local elevation models (resolution 10 &#8211; 20 m) were compared with global model MERIT (resolution 25 m).The most significant methodological innovation is the ellipsoidal heights concept using straightforward calculation of mass/bathymetric corrections in respect to the ellipsoid instead of using the geophysical indirect effect computation. Our specially developed program Toposk was used for mass/bathymetric correction calculation (the standard distance of 166.7 km was used for the first version of the map) as well as for the calculation of lake corrections. Mass corrections amount to hundreds of mGal, while the lake corrections reach more than 5 mGal locally. Atmospheric effect taking into account topography was also calculated and compared with standard atmospheric correction.&#160;

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Analysis of gravity anomaly and seismicity in Bali region

International Journal of Physical Sciences and Engineering ◽

10.53730/ijpse.v5n3.1723 ◽

2021 ◽

Vol 5 (3) ◽

pp. 34-43

Author(s):

Alfha Abrianto L. Tobing ◽

I Ketut Sukarasa ◽

Mahmud Yusuf

Keyword(s):

Gravity Anomaly ◽

Bouguer Anomaly ◽

Secondary Data ◽

Coefficient Of Determination ◽

Satellite Gravity ◽

Mapping Tool ◽

Anomaly Map ◽

Bouguer Anomaly Map ◽

Gravity Interpretation ◽

Earthquake Data

This study aims to determine the value of the gravity anomaly in the Bali region, identify the fault structure in the Bali region using gravity interpretation and analyze the relationship between gravity anomaly and seismicity in the Bali region. The data used is secondary data, namely satellite gravity anomaly data obtained from the topex website and earthquake data obtained from the Indonesian Agency for Meteorological, Climatological, and Geophysics (BMKG) catalog. Data processing in this study was done using gravity and Second Vertical Derivative (SVD) methods. We used Surfer15 software, Oasis Montaj, and the Generic Mapping Tool (GMT). The results of the complete Bouguer anomaly map show the anomalous value of the study area between 10-220 mGal, regional anomaly 40-190 mGal, and the residual anomaly between (-120)-60 mGal. Judging from the SVD contour map that has included earthquake data in the Bali region for the 2008-2020 period, the type of fault in the Seririt Fault, Tejakula Fault, and Fault around Mount Agung is a thrust fault. Judging from the value of the coefficient of determination, it shows that 99% of the seismicity value is influenced by gravity anomaly. The higher the value of the gravity anomaly, the higher the seismicity value.

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

Al-Fiziya: Journal of Materials Science, Geophysics, Instrumentation and Theoretical Physics ◽

10.15408/fiziya.v4i1.20235 ◽

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.

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Geological interpretation of offshore Central Sumatra basin using topex satellite gravity data

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/944/1/012034 ◽

2021 ◽

Vol 944 (1) ◽

pp. 012034

Author(s):

I Setiadi ◽

J Widodo ◽

T B Nainggolan

Keyword(s):

Spectral Analysis ◽

Gravity Data ◽

Mass Density ◽

Bouguer Anomaly ◽

Hydrocarbon Exploration ◽

Band Pass Filter ◽

Satellite Gravity ◽

Pass Filter ◽

Band Pass ◽

Central Sumatra

Abstract Topex is a geodetic satellite to map earth surface topography with very high precision. Two types of data can be obtained from Topex satellite, namely topographic and free-air gravity field data. Then, it is processed to produce Bouguer anomaly which will be used to interpret the subsurface geology of a specific study area. The purpose of this study was to delineate sedimentary basin and basement configurations. The methods used in this research are spectral analysis, band-pass filter and 2D forward modeling. The spectral analysis results show the average thickness of the sedimentary rocks is 2.1 km. Sub-basin patterns based on the band-pass filter are 7 sedimentary sub-basins and the structural patterns found in this area comprise basement height, graben and fault. The 2D modeling results show that the bedrock in the eastern part of the Central Sumatra basin is granitic with a mass density value of 2.67 gr/cc and the layer above the bedrock is interpreted as a sedimentary rock with a mass density value of 2.35 gr/cc. Analysis of the gravity data shows significant results as initial information to delineate sedimentary sub-basin and regional structure to enhance information to the next stage of hydrocarbon exploration.

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ANALYSIS OF GRAVITY DATA NEAR CONTINENTAL MARGINS

The APPEA Journal ◽

10.1071/aj73014 ◽

1974 ◽

Vol 14 (1) ◽

pp. 114

Author(s):

A. J. Flavelle ◽

Y. Yoshimura

Keyword(s):

Continental Margin ◽

Sea Water ◽

Gravity Data ◽

Bouguer Anomaly ◽

Sedimentary Basins ◽

Continental Margins ◽

Upper Crust ◽

Anomaly Map ◽

Bouguer Anomaly Map ◽

Thickness Variations

In general large, thick sedimentary basins are delineated by negative gravity features. The gravity data are usually expressed in the form of Bouguer anomaly contours.Ordinary Bouguer anomaly data fail as a direct indicator of approximate sedimentary thickness in zones on and adjacent to the continental margin. Rapid variations in crustal and ocean thickness cause gravitational variations which are not removed during the computation of Bouguer anomaly values.If crustal thickness variations are known or can be calculated then gravitational corrections can be made which take this factor into account. Similar corrections for variations in sea water attraction can be made. The resultant Bouguer anomaly map, corrected for those variations, will indicate in more definite terms density variations in the material of the upper crust. In particular Bouguer anomaly patterns over continental areas adjacent to the continental slope can be more easily interpreted in terms of sedimentary thickness.

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Gravity Survey of King Fahd University of Petroleum and Minerals Dammam Dome, Saudi Arabia

10.2118/204564-ms ◽

2021 ◽

Author(s):

Pantelis Soupios ◽

Alexandros Stampolidis ◽

Maurizio Fedi ◽

SanLinn Kaka ◽

Khalid Al-Ramadan ◽

...

Keyword(s):

Saudi Arabia ◽

Gravity Data ◽

Bouguer Anomaly ◽

3D Models ◽

Low Noise ◽

Gravity Survey ◽

Differential Gps ◽

Gravity Measurements ◽

Anomaly Map ◽

Bouguer Anomaly Map

Abstract The study area is a part of Dammam Dome that is situated at King Fahd University of Petroleum & Minerals (KFUPM) campus, Dhahran, Kingdom of Saudi Arabia. The gravity survey was conducted as a pilot case study to explore part of Dammam Dome in greater detail. Gravity data were collected solely during night hours due to low noise levels. A significant part of the survey was conducted during the summer holiday period, , when there was no student are on campus. A total of 235 gravity measurements were made using a Scintrex CG5 gravitometer, while a Trimble R10+ differential GPS (DGPS) was used to measure the stations’ location and elevation with the highest accuracy. All gravity data were reduced using several algorithms, and their outcomes were cross-compared. The Complete Bouguer anomaly map for the campus was then generated. Several enhancement filters including edged detection and shallow to deeper source separation were applied. Data were inverted, and 2.5D and 3D models were created to image the subsurface conditions. The main purpose of this study is to better understand the subsurface geology, tectonic settings of the Dammam Dome by applying the high-resolution gravity method before carrying out any comprehensive geophysical (seismic) 3D survey.

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DETECTION OF GROSS ERRORS IN THE GRAVIMETRIC DATABASE OF THE RIO GRANDE DO SUL STATE

Brazilian Journal of Geophysics ◽

10.22564/rbgf.v30i3.185 ◽

2012 ◽

Vol 30 (3) ◽

Author(s):

Marilei Bender Xavier ◽

Silvia Beatriz Alves Rolim

Keyword(s):

Gravity Data ◽

Bouguer Anomaly ◽

Rio Grande ◽

Shuttle Radar Topography Mission ◽

Rio Grande Do Sul ◽

Digital Elevation ◽

Anomaly Map ◽

Bouguer Anomaly Map ◽

Elevation Model ◽

Gravity Recovery

Since 1950, ground gravity data of the Rio Grande do Sul State (RS), Brazil, have been systematically collected by the Department of Geodesy of the Universidade Federal do Rio Grande do Sul (UFRGS) and other institutions in a total of 7.218 points. This paper proposes three methods for detection of gross errors in this database, based on: 1) the digital elevation model of Shuttle Radar Topography Mission (SRTM), 2) the Gravity Recovery and Climate Experiment (GRACE), and 3) the interpolated observations of ground gravity observations (Bouguer anomaly). The 1st method identified 217 points of altimetry, representing 3.00% of the database. The 2nd identified 645 points of gravity observations, representing 8.93% of the database. The3 rd method identified 60 points of land gravimetric observations, representing 0.83% of the database. The criterion to eliminate the observations was based on the recognition of coincident outliers in, at least, 2 methods. The matching points of coarse errors among altimetry, gravity and Bouguer anomaly were grouped in 177 points, representing 2.45% of the database. These points were considered gross errors and were erased from the database. After cleaning the database, we focused in the preliminary interpretation of the Bouguer anomaly map of the RS, recognizing a direct association of the main regional geologic units with four well-defined geophysical domains.

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