Bright spots, milligals, and gammas

Geophysics ◽  
1982 ◽  
Vol 47 (12) ◽  
pp. 1693-1705
Author(s):  
Alan O. Ramo ◽  
James W. Bradley
Keyword(s):  
Seismic Data ◽  
Magnetic Data ◽  
Amplitude Analysis ◽  
Seismic Amplitude ◽  
The North ◽  
Gravity And Magnetic ◽  
Amplitude Anomaly ◽  
North Edge ◽  
Gravity And Magnetic Data ◽  
Seismic Anomaly

Spatially discontinuous high‐amplitude seismic reflections were encountered in seismic data acquired in the early 1970s in northeast Louisiana and southwest Arkansas. Large acoustic impedance contrasts are known to result from gaseous hydrocarbon accumulations. However, amplitude anomalies may also result from large density and velocity contrasts which are geologically unrelated to hydrocarbon entrapment. A well drilled on the northeast Louisiana amplitude anomaly encountered 300 ft of rhyolite at a depth of 6170 ft. Subsequent gravity and total field magnetic profiles across the feature revealed the presence of 0.2 mgal and 17 gamma anomalies, respectively. The measured magnetic susceptibility of the rhyolite was 0.0035 emu and the measured density contrast was [Formula: see text]. Model studies based on the seismically determined areal extent of the anomaly and the measured thickness of rhyolite accounted for the observed gravity and magnetic anomalies. The southwest Arkansas amplitude anomaly was a sheet‐like reflection which terminated to the north and west within the survey area. Two north‐south gravity profiles exhibited a negative character over the sheet‐like reflector but did not exhibit a clear spatial correlation with the north limit of the seismic anomaly. Two north‐south magnetic profiles exhibited tenuous 4 gamma anomalies which appeared to be spatially correlated with the interpreted north edge of the seismic anomaly. A subsequent wildcat well encountered no igneous material but did penetrate 200 ft of salt at about 7500 ft. Reassessment of the gravity and magnetic data indicated that this seismic amplitude anomaly is not attributable to an intrasedimentary igneous source; it suggested a salt‐related 0.2 to 0.3 mgal minimum coextensive with the observed seismic amplitude anomaly. Present amplitude analysis technology would treat these seismic data with suspicion. However, gravity and magnetic data acquisition can provide a relatively inexpensive means for evaluation and verification of amplitude anomalies and thus should be an adjunct for land seismic exploration utilizing amplitude analysis.

The Use of Potential Fields in the Search for Potential Fields in the Faroe-Shetland Area

1998 ◽  
Vol 1 (05) ◽  
pp. 476-484 ◽  
Author(s):  
Richard Morgan ◽  
Colm Murphy
Keyword(s):  
Continental Margin ◽  
Seismic Data ◽  
Magnetic Data ◽  
3D Seismic ◽  
The North ◽  
Gravity And Magnetic ◽  
Basin Scale ◽  
The North Sea ◽  
Gravity And Magnetic Data ◽  
3D Seismic Data

This paper (SPE 51828) was revised for publication from paper SPE 38503, first presented at the 1997 SPE Offshore Europe Conference, Aberdeen, 9-12 September. Original manuscript received for review 9 September 1997. Revised manuscript received 6 July 1998. Paper peer approved 10 July 1998. Summary Fundamental geological and environmental differences exist between the basins of the North Sea and the basins of the northwest European continental margin, and strategies for success in the North Sea have not necessarily transferred directly to the continental margin. As a result, exploration outcomes to date have been somewhat disappointing, with one or two notable exceptions. Furthermore, a change in the approach to acreage evaluation places increasing levels of reliance on seismic data, specifically three-dimensional (3D) data, to tie down prospects before drilling. This approach focuses down rapidly to the prospect scale, and, although allowing detailed analysis of target structures, there is a risk of creating a gap in understanding between the geological processes observed at the basin scale and those at the prospect scale. A strategy to bridge this gap has drawn upon the wider family of geophysical data, namely gravity and magnetic data, in conjunction with a conventional, broad, regional grid of two-dimensional (2D) seismic data. These data have been worked together to construct a basin scale framework into which 3D seismic data acquisition can be planned and the results interpreted.At the regional scale, satellite-derived gravity coverage has enabled the removal of the effects of Tertiary seafloor spreading, allowing structures on the northwest European continental margin to be viewed in context with the geology of East Greenland.At the basin scale, basinal elements have been identified and correlated among seismic, gravity, and magnetic data. Controlling faults have been mapped, and the timing of basin formation inferred from trend and geometry, with implications for source rock distribution.At the license block scale, the segmentation of basin margins has been revealed by high spatial resolution magnetic data with implications for both trapping potential and the control of sediment supply into the basins. The fusion of interpretations made from the different types of geophysical data creates a scale of observation range that stretches from tectonic plates to prospective structures. The resulting geological framework has sufficient scale overlap to relate immediately to the level of detail available from 3D seismic data. Moreover, the broader perspective may ensure that those seismic data are acquired in the correct part of the basin in the first place. P. 476

Petroleum potential of the offshore southern Carnarvon Basin—insights from new Geoscience Australia data

2011 ◽  
Vol 51 (2) ◽  
pp. 746
Author(s):  
Irina Borissova ◽  
Gabriel Nelson
Keyword(s):  
Seismic Data ◽  
Source Rocks ◽  
Magnetic Data ◽  
Long Distance ◽  
Potential Field Data ◽  
Petroleum Potential ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Data ◽  
Insight Into ◽  
Carnarvon Basin

In 2008–9, under the Offshore Energy Security Program, Geoscience Australia (GA) acquired 650 km of seismic data, more than 3,000 km of gravity and magnetic data, and, dredge samples in the southern Carnarvon Basin. This area comprises the Paleozoic Bernier Platform and southern part of the Mesozoic Exmouth Sub-basin. The new seismic and potential field data provide a new insight into the structure and sediment thickness of the deepwater southernmost part of the Exmouth Sub-basin. Mesozoic depocentres correspond to a linear gravity low, in water depths between 1,000–2,000 m and contain between 2–3 sec (TWT) of sediments. They form a string of en-echelon northeast-southwest oriented depressions bounded by shallow-dipping faults. Seismic data indicates that these depocentres extend south to at least 24°S, where they become more shallow and overprinted by volcanics. Potential plays in this part of the Exmouth Sub-basin may include fluvio-deltaic Triassic sandstone and Lower–Middle Jurassic claystone source rocks sealed by the regional Early Cretaceous Muderong shale. On the adjoining Bernier Platform, minor oil shows in the Silurian and Devonian intervals at Pendock–1a indicate the presence of a Paleozoic petroleum system. Ordovician fluvio-deltaic sandstones sealed by the Silurian age marine shales, Devonian reef complexes and Miocene inversion anticlines are identified as potential plays. Long-distance migration may contribute to the formation of additional plays close to the boundary between the two provinces. With a range of both Mesozoic and Paleozoic plays, this under-explored region may have a significant hydrocarbon potential.

scholarly journals The hidden sedimentary basin underneath the Quaternary volcanic unit in Bogor and Kendeng area

2021 ◽  
Vol 47 (2) ◽  
pp. 25-47
Author(s):  
Erlangga Septama ◽  
C. Prasetyadi ◽  
A Abdurrokhim ◽  
T. Setiawan ◽  
P.D. Wardaya ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Sediment Supply ◽  
Passive Margin ◽  
Magnetic Data ◽  
Rock Samples ◽  
Petroleum Systems ◽  
The North ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Data ◽  
East West

The Java Island is an active volcanic arc that experiences several volcanism episodes, which gradually changes from South to North from the Late Oligocene to Pleistocene, following the subduction of the Australian plates underneath the Eurasian plates. During the Eocene, the southern and northern part of Java was connected as one passive margin system with the sediment supply mainly comes from Sundaland in the north.  The compressional tectonics creates a flexural margin and a deep depression in the central axis of Java Island and acts as an ultimate deep-sea depocenter in the Neogene period. In contrast to the neighboring Northwest and Northeast Java Basins in the Northern edges of Java Island, the basin configuration in the East-West trending depression in median ranges of Java (from Bogor to Kendeng Troughs) are visually undetected by seismic due to the immense Quaternary volcanic eruption covers.Five focused window areas are selected for this study. A total of 1,893 Km sections, 584 rock samples, 1569 gravity and magnetic data, and 29 geochemical samples (rocks, oil, and gas samples) were acquired during the study. Geological fieldwork was focused on the stratigraphic unit composition and the observable features of deformation products from the outcrops. Due to the Paleogene deposit exposure scarcity in the Central-East Java area, the rock samples were also collected from the mud volcano ejected materials in the Sangiran Dome.The distinct subsurface configuration differences between Bogor and Kendeng Troughs are mainly in the tectonic basement involvement and the effect of the shortening on the formerly rift basin. Both Bogor and Kendeng Troughs are active petroleum systems that generate type II /III Kerogen typical of reduction zone organic material derived from transition to the shallow marine environment. The result suggests that these basins are secular from the neighboring basins with a native petroleum system specific to the palaeogeographical condition during the Paleogene to Neogene periods where the North Java systems (e.g., Northwest and Northeast Java Basin) was characterized by oxidized terrigenous type III Kerogen.

scholarly journals Marine geophysical investigations offshore East Greenland

1983 ◽  
Vol 115 ◽  
pp. 93-100
Author(s):  
H.C Larsen
Keyword(s):  
Seismic Data ◽  
Seismic Refraction ◽  
Magnetic Data ◽  
Seismic Profiles ◽  
East Greenland ◽  
Gravity And Magnetic ◽  
Marine Gravity ◽  
Refraction Seismic ◽  
Regional Project ◽  
Gravity And Magnetic Data

During August and September 1982 a marine geophysical survey was conducted on the East Greenland Shelf. The survey was part of the ongoing regional project NAD (Larsen & Andersen, 1982; Andersen et al., 1981; Risum, 1980; Larsen & Thorning, 1980). In all 2794 km of 30-fold multi-channel seismic data and marine gravity and magnetic data were acquired (fig. 33). The object of the NAD programme is to acquire regional coverage of aeromagnetic, multichannel seismic refiection, seismic refraction (sonobuoy), marine gravity and magnetic data of the East Greenland Shelf between latitudes 60° N and 78°N. Aeromagnetic data comprising 63000 line kilometres were acquired in 1979 (Larsen & Thorning, 1980) and 5000 km of marine geophysical data were acquired in 1980 and 1981 (Larsen & Andersen, 1982; Andersen et al., 1981). This year the final data for the project were collected. Thus, a total of 7800 km of multi-channel refiection seismic data and 50 sonobuoy refraction seismic profiles of 20 to 70 km length have been acquired (fig. 33). In addition, marine gravity and magnetics were run at most lines.

The extent of igneous rocks of the South China Sea based on the correlational analyses of gravity and magnetic data

2020 ◽  
Author(s):  
Min Yang ◽  
Wanyin Wang ◽  
Xiaolin Ji ◽  
Tao Ma ◽  
Jie Ma ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
The South China Sea ◽  
Igneous Rocks ◽  
Magnetic Data ◽  
The South ◽  
China Sea ◽  
The North ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Data

<p>The South China Sea is the biggest conjugate marginal sea in the West Pacific Ocean, which is influenced by the Eurasian plate, the Pacific plate, and the Indo-Australian plate. There have developed continental tectonic margins with different characters after experiencing subduction, collision, strike-slip and so on since the Mesozoic and Cenozoic (Yao et al., 2004; Zhang et al., 2014). However, the igneous rock can be regarded as a recorder to reveal some information of evolution and deep geodynamics of the South China Sea, which helps us to improve understanding of the continental rifting, the seafloor spreading, the formation of deep water basins and the process of hydrocarbon accumulation(Zhang et al., 2016).<br>The igneous rocks are studied by multiple types of data that are magnetic data, seismic profiles, and drilling data in the previous studies. Hence, there are bunch of research results about the igneous rocks that contain the reason and time of formation, the distribution of space, the period of eruption in the north of the South China Sea because of the abundant datasets (Zou et al., 1993,1995; Zhou et al., Yan and Liu, 2005; Xu et al., 2013; Zhang et al., 2013; Zhang et al., 2014; Zhang et al., 2015; Zhang et al., 2016), in addition, the Pearl River Mouth Basin is the most famous one among all of the basins in the South China Sea. However, the researchs related to the south of the South China Sea where are the deep-sea are far less knowledgeable about the distribution of the igneous rocks than the north because of the limitation of datasets that are poor quality and less quantity (Yao et al., 2004; Li et al., 2010; Hui et al., 2016), which lead to the less researches with respect to the big area of the South China Sea.<br>The followings can be concluded from the previous studies. The northern and continental margin of the South China Sea are distributed by Cenozoic extrusive rocks with high susceptibility and low density and Yanshanian intrusive rocks with low susceptibility and density (Hao et al., 2009; Lu et al., 2011; Hui et al., 2016), the Central Sub-basin is covered by Cenozoic extrusive rocks (Yan and Liu, 2005; Hui et al., 2016), however, there are few distributions of the Yanshanian intrusive rocks in the Southern South China Sea (Zhang et al., 2015; Hui et al., 2016). In this study, a new method, the fusion of gravity and magnetic data, is applied to detect the distribution of the igneous rocks in order to provide more geophysical data in the South China Sea.</p>

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