The role of airborne geophysics for detecting hydrocarbon microseepages and related structural features: The case of Remanso do Fogo, Brazil

Geophysics ◽  
2012 ◽  
Vol 77 (2) ◽  
pp. B35-B41 ◽  
Author(s):  
Julia B. Curto ◽  
Augusto C.B. Pires ◽  
Adalene M. Silva ◽  
Álvaro P. Crósta
Keyword(s):  
Gamma Ray ◽  
Sedimentary Cover ◽  
Structural Features ◽  
Magnetic Data ◽  
Gamma Ray Spectrometry ◽  
Horizontal Gradient ◽  
Near Surface ◽  
Residual Values ◽  
Basement Structures ◽  
New Occurrences

The first direct indication of hydrocarbon occurrence in Remanso do Fogo area (Minas Gerais State, Brazil) was the existence of microseepages. However, Quaternary sedimentary cover in the area made the identification of new occurrences and associated controlling structures quite difficult. This study investigated the spatial distribution of hydrocarbon related gases in shallower to intrasedimentary depths in Remanso do Fogo area, using airborne gamma-ray spectrometry and magnetic data. The geophysical data were processed using techniques designed to suppress the influence of regional geological signatures. Known and possible new occurrences of microseepages were detected by mapping low residual potassium values and high uranium residual values in relation to potassium, termed as DRAD values, which resulted from the subtraction of potassium from uranium residual values, using a Thorium (Th)-normalizing approach. The validation of these occurrences was done based on existing gas geochemistry data in the soil. For the magnetic data, the amplitude of the analytic signal, combined with the total horizontal gradient of the subtraction between the 1200- and 400-meter upward continuations, enhanced the northwest–southeast and east–west magnetic lineaments, which are partially related to the microseepages and the drainage of the area. The distinction of near-surface and deep signatures also allowed the general identification of intrasedimentary and basement structures, which are potentially controlling the occurrences of seepages in the area.

scholarly journals Structural features derived from a Multiscale Analysis and 2.75D Modelling of Aeromagnetic Data over the Pitoa-Figuil Area (Northern Cameroon)

2020 ◽  
Author(s):  
Voltaire Souga Kassia ◽  
Theophile Ndougsa-Mbarga ◽  
Arsène Meying ◽  
Jean Daniel Ngoh ◽  
Steve Ngoa Embeng
Keyword(s):  
Multiscale Analysis ◽  
Structural Features ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Aeromagnetic Data ◽  
Near Surface ◽  
Subsurface Structures ◽  
Northern Cameroon ◽  
Processing Techniques ◽  
Geological Formations

Abstract. In the Pitoa-Figuil area (Northern Cameroon), an interpretation of aeromagnetic data was conducted. The aim of this investigation was first to emphasize lineaments hidden under geological formations and secondly to propose two 2.75D models of the subsurface structures. Different magnetic data processing techniques were used, notably horizontal gradient magnitude, analytic signal, and Euler deconvolution. These techniques in combination with the 2.75D modelling to the aeromagnetic anomaly reduced to the equator permit to understand the stratification of the deep and near surface structures, which are sources of the observed anomalies. We managed to put in evidence and characterize 18 faults and some intrusive bodies. According to Euler's solutions, anomaly sources go up to a depth of 5.3 km.

scholarly journals Exploiting Aeromagnetic and Gravity Data Interpretation to Delineate Massif Deposits of Rehamna Area (Western Meseta-Morocco)

2021 ◽  
Vol 54 (2C) ◽  
pp. 13-28
Author(s):  
Kawtar Benyas
Keyword(s):  
Gravity Data ◽  
Precious Metals ◽  
Data Interpretation ◽  
Structural Features ◽  
Magnetic Data ◽  
Gravity Gradient ◽  
Horizontal Gradient ◽  
Geological Structures ◽  
Magnetic Signatures ◽  
First Vertical Derivative

The analysis of the magnetic signatures and gravity gradient values of the Rehamna Massif south of the Moroccan Western Meseta by using Geosoft Oasis Montaj 7.0.1 software, allowed us to detect several useful anomalies to be exploited and which are related to magmatic bodies and structural features within the study area. These data were analyzed by applying several techniques, including the horizontal gradient filters combined with the first vertical derivative. Subsurface structures; such as geological boundaries, faults, dykes and folds, were visualized as lineaments on geophysical maps, then results were compared with structural features provided by previous studies in the region. Thus, the Rehamna Massif structural map shows sets of linear features which may represent faults or boundaries of geological structures, which can be either faults or boundaries of geological structures, and they are mostly oriented in the directions: N-S, NNE-SSW, NE-SW, E-W with the predominance of the NNE-SSW to NE-SW directions. In addition, the super position of the minerals bearing beds or formations were distinguished from gravity and magnetic data processing results. Some of the recognized anomalies are related to the existence of precious metals which belong to the granitic bodies within the study area.

scholarly journals Radiometric Surveys for Detection of Uranium in Dhofar Region, Sultanate of Oman

2019 ◽  
Vol 24 (1) ◽  
pp. 36
Author(s):  
Narasimman Sundararajan ◽  
Bernhard Pracejus ◽  
Salah Al- Khirbash ◽  
Talal Al-Hosni ◽  
Ala Ebrahimi Ebrahimi ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Radioactive Decay ◽  
Sampling Interval ◽  
Uranium Mineralization ◽  
Gamma Ray Spectrometry ◽  
Sultanate Of Oman ◽  
Near Surface ◽  
The World ◽  
Uranium Exploration ◽  
Proterozoic Basement

The Proterozoic basement of the Dhofar region of the Sultanate of Oman might be considered as a potential source of Uranium mineralization like other Proterozoic basins of the world, which collectively contribute 30%-40% to the global production.  Uranium exploration assumes great importance in this part of the world and therefore geochemical and geophysical exploration for Uranium was initiated.  Initial, random sampling of the study area with Gamma ray spectrometry as well as in situ XRF (Xray Florescence) analysis indicated the presence of   around 30-40 ppm of Uranium. Since Gamma ray spectrometry results in the calculation of the heat produced during radioactive decay of Potassium (K), Uranium (U) and Thorium (Th) within the rocks in the study area, measurements were acquired along eleven traverses of varying length from 100-250 m at a traverse interval of 20 m and sampling interval of 10 m. Individual plots of the concentrations  of radioelements such as U, K and Th have shown favorable anomalous radioactive sources. Besides this, Uranium to Thorium (eU/eTh) and Uranium to Potassium (eU/K) ratio plots have been presented and the alteration zones associated with Uranium mineralization through all traverses have been identified. Further, the generated composite ternary image based on the combination of K, Th and U from Gamma ray spectrometry determines different relative amounts of radioelements and paves the way for deciphering the level of radioactivity in the study area. However, there seems to be no presence of strong Uranium anomalies in the near surface of the limited study area. As the study area is heavily faulted, the depth to concealed  subsurface fault structures  is  estimated to be around  64 m based on Hartley spectral analysis of total magnetic anomaly (line-6). 

The relationship between uranium distribution and some major crustal features in Canada

1981 ◽  
Vol 44 (336) ◽  
pp. 425-436 ◽  
Author(s):  
A. G. Darnley
Keyword(s):  
Gamma Ray ◽  
Gravity Anomalies ◽  
Structural Features ◽  
Gamma Ray Spectrometry ◽  
Low Grade ◽  
Bouguer Gravity ◽  
Uranium Enrichment ◽  
Bouguer Gravity Anomalies ◽  
Uranium Distribution ◽  
North American Craton

AbstractThe availability of reconnaissance scale geochemical maps for large areas of Canada enables spatial associations between major crustal structures and surface uranium content to be identified. Maps of the distribution of uranium for an area greater than 2 million km2 compiled from airborne gamma-ray spectrometry data are supplemented by maps for uranium, based on stream and lake sediment and some bore hole sampling. These are examined in relation to gravity, aeromagnetic and geological maps.The radioelement distribution can be related in detail to exposed bedrock and surface geology, but in addition there is evidence of the control of uranium distribution by major structural features which are marked by granitoids containing elevated levels of radioelements; several of these granitoids are associated with large negative Bouguer gravity anomalies. The distribution of such granitoids appears to be related to ‘megashears’, as in the case of the South Mountain batholith in Nova Scotia, or zones of tension. A belt of uranium enrichment, the Athabasca axis which is characterized by uraniferous granitoids with negative Bouguer gravity anomalies and associated tension faulting extends 2500 km northeast-ward from Edmonton, Alberta to the Melville Peninsula. This structure passes under the Athabasca basin which contains many large uranium deposits. Recent evidence that granitoids enriched in radioelements can provide low-grade heat sources over periods of hundreds of millions of years, capable, in favourable situations of maintaining low-temperature hydrothermal circulation is considered to account for uranium and other mineralization in the basin. It is suggested that the transfer of radioelements into the crust at the end of the Lower Proterozoic, was a factor in the stabilization of North American craton.

scholarly journals INTERPRETATION OF RADIOMETRIC RATIOS AND MAGNETIC ANOMALIES FROM MORRO FEIO ULTRAMAFIC COMPLEX, CENTRAL-WESTERN BRAZIL

2019 ◽  
Vol 37 (3) ◽  
pp. 309
Author(s):  
Adolfo Silva ◽  
Tiago Duque ◽  
Felipe Alves
Keyword(s):  
Gamma Ray ◽  
Magnetic Anomalies ◽  
Primary Sources ◽  
Magnetic Data ◽  
Gamma Ray Spectrometry ◽  
Mineral Research ◽  
Magnetic Structures ◽  
Relative Enrichment ◽  
Ultramafic Complex ◽  
Processing Techniques

ABSTRACTThis study was performed to identify magnetic structures in depth and radiometric responses within and around Morro Feio Ultramafic Complex (MFUC) from the airborne geophysical (gamma–ray spectrometry and magnetic) data. Using processing techniques and profiles analysis, we have found eight gamma–ray spectrometry signatures and twenty–seven magnetic anomalies. The radiometric signatures are basically characterized by a K and eU relative enrichment in detriment eTh, with two of these signatures also characterized by K relative enrichment in detriment eU. Based on published works, we have interpreted the radiometric responses may be from serpentinite and possible areas with hydrothermal alterations. Regarding the magnetic anomalies, we concluded that the shallowest may be the magnetic responses of dikes, contact zones and other structures, while the deepest have sources with more complex geometries and are concentrated in central–western of MFUC, where the participation of Pt is larger. In this aspect, our results reinforce the arguments favorable to existence of Pt, Cr and Ni primary sources in depth.Keywords: mineral research, airborne geophysical, serpentinites, hydrothermal alteration.RESUMOEste estudo foi realizado com o objetivo de identificar estruturas magnéticas em profundidade e respostas radiométricas dentro e no entorno do Complexo Ultramáfico de Morro Feio (CUMF) a partir de dados aerogeofísicos (gamaespectrometria e magnetometria aérea). Utilizando técnicas de processamento e análise de perfis, encontramos oito assinaturas gamaespectrométrica e vinte e sete anomalias magnéticas. As assinaturas radiométricas caracterizam–se basicamente por um enriquecimento relativo de K e eU em detrimento eTh, com duas dessas assinaturas também sendo caracterizadas pelo enriquecimento relativo de K em detrimento eU. Com base em trabalhos publicados, interpretamos que as respostas radiométricas podem ser em virtude do serpentinito e possíveis áreas com alterações hidrotermais. Com relação às anomalias magnéticas, concluímos que as mais rasas podem ser as respostas magnéticas de diques, zonas de contato e outras estruturas, enquanto que as mais profundas possuem fontes com geometrias mais complexas e se concentram no centro–oeste do CUMF, onde a participação de Pt é maior. Neste aspecto, nossos resultados reforçam os argumentos favoráveis a existência de fontes primárias de Pt, Cr e Ni em profundidade.Palavras-chave: pesquisa mineral, aerogeofísica, serpentinitos, alteração hidrotermal.

scholarly journals Evidence of Major Structural Features over the Pan-African Domain in the Bertoua-Mbangue Area (East Cameroon) from a Multiscale Approach of Modeling and Interpretation of Aeromagnetic Data

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Owono Amougou Olivier Ulrich Igor ◽  
Ndougsa Mbarga Theophile ◽  
Meying Arsène ◽  
Assembe Stephane Patrick ◽  
Ngoh Jean Daniel ◽  
...  
Keyword(s):  
High Amplitude ◽  
Structural Features ◽  
Short Wave ◽  
The Other ◽  
Horizontal Gradient ◽  
Multiscale Approach ◽  
Magnetic Intensity ◽  
Aeromagnetic Data ◽  
Pan African ◽  
Basement Structures

The aim of this study is to investigate crustal structures from East Cameroon, using aeromagnetic data. The modeling of aeromagnetic data is conducted using the Oasis Montaj 8.0 software. The total magnetic intensity map reduced to the equator (RTE-TMI) shows important anomalies features, namely, the Northern East magnetic anomalies of high amplitude, the Southwest where very low values of the magnetic intensity were observed, and a corridor with negative values relatively high, separating the anomalies. The horizontal gradient map shows on the one hand brittle and folded structures carried out in the area of study and on the other hand various rectilinear, narrow, and short-wave anomalies that can be classified as a family of little faults. The maxima observed on the RTE-TMI maps are correlated to intrabasement contacts; and the map derived from Euler’s solutions permitted to evaluate the depth of the geological accidents observed from the other filters. This map also reveals new faults with a depth greater than 5000 m. The lineaments identified in the Southwestern part could be linked to the Pan-African orogeny and seem to correspond to deep-seated basement structures, which are referred to the tectonic boundary between Congo Craton and the Pan-African orogeny belt. A 23/4-D modeling confirmed the observations derived from the RTE-TMI and HGM maps analyses. It shows intrusive bodies composed of gneiss and porphyroid granite and some domes with their roof situated at various depths not exceeding 1800 m from the surface. The structural map of the study area shows the trending of the structural features observed, namely, NE-SW, NW-SE, ENE-WSW, and WNW-ESE, respectively, while the E-W and N-S are secondary orientation of the observed tectonic evidence. Moreover, circular anomalies observed over the area are assimilated to intrusions of high magnetic materials or to granitic domes.

scholarly journals Soil Gas Measurements of Radon, CO2 and Hydrocarbon Concentrations as Indicators of Subsurface Hydrocarbon Accumulation and Hydrocarbon Seepage

2021 ◽  
Vol 13 (7) ◽  
pp. 3840
Author(s):  
Marko Cvetković ◽  
Josipa Kapuralić ◽  
Marija Pejić ◽  
Iva Kolenković Močilac ◽  
David Rukavina ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Soil Gas ◽  
Gamma Ray Spectrometry ◽  
Hydrocarbon Accumulation ◽  
Near Surface ◽  
Migration Pathway ◽  
Sampling Points ◽  
Oil Seepage ◽  
Gas Measurements ◽  
Migration Pathways

Soil gas measurements of radon (222Rn), CO2, and hydrocarbon concentrations, as well as gamma-ray spectrometry, were conducted at two separate locations to estimate the measurement results for known locations of hydrocarbon accumulations in the subsurface and oil seepage on the surface. The aim of the study was to confirm the applicability of the method for identifying migration pathways (e.g., faults) and to detect possible seepages of hydrocarbons to the surface as well as to investigate possible health issue potential about the soil gas analysis results. Site A investigations were performed with a large number of sampling points to provide sufficient spatial coverage to capture the influence of subsurface lithologic variability as well as the influence of the migration pathway on the measured parameters. For the investigation of site B, sampling points were positioned to reflect the situation between the area above producing hydrocarbon fields and areas with no confirmed accumulation. The results presented show that it is possible to distinguish the near-surface lithology (gamma-ray spectrometry), characterize the migration pathway, and indicate the area of oil seepage at the surface. Areas above the known hydrocarbon accumulations generally have elevated radon concentrations and detectable heavier hydrocarbons with sporadic methane in soil gas, which contrasts with the lower radon levels and lack of detectable heavier hydrocarbons in soil gas in the area with no confirmed hydrocarbon accumulation in the subsurface.

Three-dimensional distribution of igneous rocks near the Pebble porphyry Cu-Au-Mo deposit in southwestern Alaska: Constraints from regional-scale aeromagnetic data

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. B63-B79 ◽  
Author(s):  
Eric D. Anderson ◽  
Wei Zhou ◽  
Yaoguo Li ◽  
Murray W. Hitzman ◽  
Thomas Monecke ◽  
...  
Keyword(s):  
Porphyry Copper ◽  
Regional Scale ◽  
Copper Deposit ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Aeromagnetic Data ◽  
Near Surface ◽  
Magnetic Inversion ◽  
Tilt Derivative ◽  
Southwestern Alaska

Aeromagnetic data helped us to understand the 3D distribution of plutonic rocks near the Pebble porphyry copper deposit in southwestern Alaska, USA. Magnetic susceptibility measurements showed that rocks in the Pebble district are more magnetic than rocks of comparable compositions in the Pike Creek–Stuyahok Hills volcano-plutonic complex. The reduced-to-pole transformation of the aeromagnetic data demonstrated that the older rocks in the Pebble district produce strong magnetic anomaly highs. The tilt derivative transformation highlighted northeast-trending lineaments attributed to Tertiary volcanic rocks. Multiscale edge detection delineated near-surface magnetic sources that are mostly outward dipping and coalesce at depth in the Pebble district. The total horizontal gradient of the 10-km upward-continued magnetic data showed an oval, deep magnetic contact along which porphyry deposits occur. Forward and inverse magnetic modeling showed that the magnetic rocks in the Pebble district extend to depths greater than 9 km. Magnetic inversion was constrained by a near-surface, 3D geologic model that is attributed with measured magnetic susceptibilities from various rock types in the region. The inversion results indicated that several near-surface magnetic sources with moderate susceptibilities converge with depth into magnetic bodies with higher susceptibilities. This deep magnetic source appeared to rise toward the surface in several areas. An isosurface value of 0.02 SI was used to depict the magnetic contact between outcropping granodiorite and nonmagnetic sedimentary host rocks. The contact was shown to be outward dipping. At depths around 5 km, nearly the entire model exceeded the isosurface value indicating the limits of nonmagnetic host material. The inversion results showed the presence of a relatively deep, northeast-trending magnetic low that parallels lineaments mapped by the tilt derivative. This deep low represents a strand of the Lake Clark fault.

Sign in / Sign up

Export Citation Format

Share Document