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

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.

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

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.

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

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.

Correlation Of Residual Anomaly and Isoseismal Map by Using Power Spectral Density Method in Palu City Region

This research was conducted to see the correlation between residual anomaly map, geological map, and isoseismal map and how they contribute to the determination of earthquake-prone areas. Moreover, the area studied is an area that is difficult to obtain geophysical data such as urban areas. The residual anomaly is obtained by calculating the bouguer anomaly from elevation data and free-air correction satellite, which then through the FFT process changes the spatial domain to the frequency domain in MATLAB. Thus, it can separate regional anomaly maps with residuals. Using the overlaying technique on two maps, namely residual anomaly maps with isoseismal, a clear correlation was found between the residual anomaly value and the impact of the earthquake as well as the validation of the geological map in the area

Identification of Subsurface Rock Structure of Non-Volcanic Geothermal Systems Based on Gravity Anomalies (Terak Village, Central Bangka Regency)

Geothermal manifestations on Bangka Island are found in the villages of Terak, Pemali, Sungailiat/Pelawan, Dendang, Permis, and Nyelanding. The manifestation of hot water in Terak Village, Central Bangka Regency is in the form of 3 hot springs with a surface temperature of 55ᵒC this research is to be carried focus on the structure of the subsurface rock layers using the geophysical method, namely the gravity method. The data used are topography and Free Air Anomaly. The data processing is in the form of Bouguer Correction and Terrain Correction to obtain the Complete Bouguer Anomaly (CBA) value. Then the CBA value is separated from regional anomalies and residual anomalies using the upward continuation method, as well as 2D modeling interpretation (forward modeling). From the research results, it is known that the subsurface rock structure of the non-volcanic geothermal system in Terak Village in the form of sandstone (2.28 – 2.49 gr/cm3) at a depth of 0 – 1.44 km is estimated as caprock, granite (2.77 – 2.78 gr/cm3) at a depth of 0 – 1.8 km is estimated as reservoir rock, and diorite rock (2.87 – 2.99 gr/ cm3) at a depth of 0 – 2 km is estimated as basement rock.

Preliminary Study of Probolinggo Active Fault in East Java Based on Gravity Method

The Gravity Method based on TOPEX satellite data is a one of geophysical method which from satellite observations. The gravity method investigate the gravitational field from one to another observation point. The principle of this method has the ability to distinguish the mass material density from its environment, so that the subsurface structure can be identified. In this research, gravity method is used to identify subsurface structures that are suspected of Probolinggo Fault and identify the rock lithology. From TOPEX we get free air anomaly and then applied the correction process to obtain Complete Bouguer Anomaly (CBA) value. The CBA value is processed interpolation to create CBA map, and then the map is filtered by butterworth to obtain regional and residual maps. The value of high gravity acceleration is 0.076 - 19.74 mGal indicating compact rocks. Meanwhile, based on the residual anomaly map, the value of smaller gravity acceleration is -0.92 - 0.9 mGal indicates lower compacting rocks with smaller mass. The gravity acceleration contrast on the residual anomaly, on the north side of fault line (0.12 mGal to 0.45 mGal) and on the south side (-0.92 mGal to -0.043 mGal), is interpreted as normal fault. Furthermore, 3D modelling shows density value less than 2 gr/cm3 we can interpret as pyroclastic fall, in between 2 gr/cm3 until 2.4 gr/cm3 is sandstone and more than 2.4 gr/cm3 is igneous rock such as andesit. 2D slicing modelling show presence the shear fault, so we can suspect this area have oblique fault with west-east direction.

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

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.

Investigating the optimal integration of airborne, ship-borne, satellite and terrestrial gravity data for use in geoid determination

<p>Each gravity observation technique has different parameters and contributes to different pieces of the gravity spectrum. This means that no one gravity dataset is able to model the Earth’s gravity field completely and the best gravity map is one derived from many sources. Therefore, one of the challenges in gravity field modelling is combining multiple types of heterogeneous gravity datasets. The aim of this study is to determine the optimal method to produce a single gravity map of the Canterbury case study area, for the purposes of use in geoid modelling. This objective is realised through the identification and application of a four-step integration process: purpose, data, combination and assessment. This includes the evaluation of three integration methods: natural neighbour, ordinary kriging and least squares collocation. As geoid modelling requires the combination of gravity datasets collected at various altitudes, it is beneficial to be able to combine the dataset using an integration method which operates in a three-dimensional space. Of the three integration methods assessed, least squares collocation is the only integration method which is able to perform this type of reduction. The resulting product is a Bouguer anomaly map of the Canterbury case study area, which combines satellite altimetry, terrestrial, ship-borne, airborne, and satellite gravimetry using least squares collocation.</p>

Investigating the optimal integration of airborne, ship-borne, satellite and terrestrial gravity data for use in geoid determination

<p>Each gravity observation technique has different parameters and contributes to different pieces of the gravity spectrum. This means that no one gravity dataset is able to model the Earth’s gravity field completely and the best gravity map is one derived from many sources. Therefore, one of the challenges in gravity field modelling is combining multiple types of heterogeneous gravity datasets. The aim of this study is to determine the optimal method to produce a single gravity map of the Canterbury case study area, for the purposes of use in geoid modelling. This objective is realised through the identification and application of a four-step integration process: purpose, data, combination and assessment. This includes the evaluation of three integration methods: natural neighbour, ordinary kriging and least squares collocation. As geoid modelling requires the combination of gravity datasets collected at various altitudes, it is beneficial to be able to combine the dataset using an integration method which operates in a three-dimensional space. Of the three integration methods assessed, least squares collocation is the only integration method which is able to perform this type of reduction. The resulting product is a Bouguer anomaly map of the Canterbury case study area, which combines satellite altimetry, terrestrial, ship-borne, airborne, and satellite gravimetry using least squares collocation.</p>

New Bouguer Anomaly Map for the Territory of the Slovenia

The existing Bouguer anomaly map, which covers the territory of the Republic of Slovenia is a few decades old. Since then, quite a few new gravimetric measurements (data) for the territory of Slovenia as well as high quality digital terrain models that are needed for creating such a map have been made available. The methodology and standards for creating gravity anomaly maps are also changing. Thus, the national Bouguer anomaly map was updated. There were some gross errors detected in the set of old gravimetric data. Additionally, the influence of new updated gravimetric data was analyzed. The comparison of the various maps and the analysis of the influence of input gravimetric data indicates that the new gravimetric data of Slovenia has a significant influence on the creation of the gravimetric anomaly maps for Slovenia (even over 30 mGals at some points).