Neotectonics of Southeast Jamaica Derived From Marine Seismic Surveys and Gravity Cores

Offshore exploration in the Exmouth Gulf commenced with seismic surveys during the early 1960s and resulted in the first well Bundegi-1 being drilled in 1978. This well, situated on the Rivoli-Bundegi Trend, encountered an interpreted residual hydrocarbon zone in the Birdrong Sandstone, an 18 m untested hydrocarbon zone in the Learmonth Formation, and tight, possibly gas bearing sandstones in the Mungaroo Formation.Modern shallow-water marine seismic data acquired by the EP 325 Joint Venture during surveys in 1987 and 1988 allowed accurate mapping of the basal Cretaceous section and the distribution of the Birdrong Sandstone. Complex structuring in the Jurassic and Triassic section was also resolved with the modern data.The Rivoli gas discovery, approximately 4.5 km northeast of Bundegi-1, was made in August 1989, with the intersection of a 10.5 m hydrocarbon column consisting mainly of gas but with a very thin oil leg (0.2 m). The Birdrong Sandstone reservoir comprises 10 m of fluvial sandstones overlain by 7 m of marginal marine sandstones and provides an important calibration point for depositional environments in this unit. The Rivoli gas pool occurs in a simple, downthrown anticline sealed by Winning Group shales. Geochemical analysis of oil extracted from core, suggests an earlier charge of 'Rough Range-type' oil, possibly generated from pre-Jurassic source rocks.Several prospects and a variety of play types are recognised and considerable exploration potential remains to be tested along the Rivoli-Bundegi Trend.

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Deep learning for low-frequency extrapolation from multioffset seismic data

Geophysics ◽

10.1190/geo2018-0884.1 ◽

2019 ◽

Vol 84 (6) ◽

pp. R989-R1001 ◽

Cited By ~ 19

Author(s):

Oleg Ovcharenko ◽

Vladimir Kazei ◽

Mahesh Kalita ◽

Daniel Peter ◽

Tariq Alkhalifah

Keyword(s):

Deep Learning ◽

Seismic Data ◽

Signal To Noise Ratio ◽

Waveform Inversion ◽

Low Frequency ◽

Low Frequencies ◽

Seismic Surveys ◽

Full Waveform ◽

Frequency Components ◽

Marine Seismic

Low-frequency seismic data are crucial for convergence of full-waveform inversion (FWI) to reliable subsurface properties. However, it is challenging to acquire field data with an appropriate signal-to-noise ratio in the low-frequency part of the spectrum. We have extrapolated low-frequency data from the respective higher frequency components of the seismic wavefield by using deep learning. Through wavenumber analysis, we find that extrapolation per shot gather has broader applicability than per-trace extrapolation. We numerically simulate marine seismic surveys for random subsurface models and train a deep convolutional neural network to derive a mapping between high and low frequencies. The trained network is then tested on sections from the BP and SEAM Phase I benchmark models. Our results indicate that we are able to recover 0.25 Hz data from the 2 to 4.5 Hz frequencies. We also determine that the extrapolated data are accurate enough for FWI application.

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Airgun blasts used in marine seismic surveys have limited effects on mortality, and no sublethal effects on behaviour or gene expression, in the copepod Calanus finmarchicus

ICES Journal of Marine Science ◽

10.1093/icesjms/fsz126 ◽

2019 ◽

Vol 76 (7) ◽

pp. 2033-2044 ◽

Cited By ~ 3

Author(s):

David M Fields ◽

Nils Olav Handegard ◽

John Dalen ◽

Christiane Eichner ◽

Ketil Malde ◽

...

Keyword(s):

Escape Response ◽

Field Experiments ◽

Sublethal Effects ◽

Low Frequency ◽

Calanus Finmarchicus ◽

Sensory Threshold ◽

Seismic Surveys ◽

Commercially Important ◽

Or Gene ◽

Marine Seismic

Abstract Seismic surveys use airguns that emit low frequency high magnitude sound to detect subsea resources and to map seabed geology. The effect of seismic blasts on Calanus spp., a key food source for commercially important fish, was assessed in field experiments. Immediate mortality of copepods was significantly different from controls at distances of 5 m or less from the airguns. Mortality 1 week after the airgun blast was significantly higher—by 9% relative to controls—in the copepods placed 10 m from the airgun blast but was not significantly different from the controls at a distance of 20 m from the airgun blast. The increase in mortality—relative to controls—did not exceed 30% at any distance from the airgun blast. Only two genes changed in response to the airgun blast; however, their function is unknown. There were no sublethal effects of the seismic blasts on the escape performance or the sensory threshold needed to initiate an escape response at any of the distances from the airgun blast that were tested. Results from these experiments suggest that seismic blasts have limited effects on the mortality or escape response of Calanus sp. within 10 m of the blast and no measurable impact at greater distances.

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SEISMIC SIGNATURES OF LARGE AIR GUNS

Geophysics ◽

10.1190/1.1440237 ◽

1971 ◽

Vol 36 (6) ◽

pp. 1162-1173 ◽

Cited By ~ 9

Author(s):

W. Harry Mayne ◽

Roy G. Quay

Keyword(s):

Energy Levels ◽

Low Frequency ◽

Experimental Tests ◽

Frequency Spectra ◽

Seismic Surveys ◽

Air Gun ◽

Absolute Energy ◽

Overall Performance ◽

Marine Seismic ◽

Effective Source

Large chamber air guns are a reliable and effective source of energy for marine seismic surveys. Air guns with chamber volumes of 300 and 1000 cubic inches demonstrate desirable low‐frequency responses and high absolute energy levels. Overall performance has been compromised, however, by the bubble effect. Previous attempts at minimizing the bubble response have resulted in loss of reliability, reduced power, or incomplete bubble suppression, or a combination thereof. In this paper, we present the results of experimental tests on air guns with 300 and 1000 cubic inch chambers and describe a divided‐chamber gun which greatly attenuates the bubble effect. Significant improvements in the width and flatness of the frequency spectra are demonstrated by analysis of the actual signatures obtained in deep water and with record sections comparing the results obtained with the standard and improved guns along an identical traverse. The bubble‐attenuating air gun simultaneously provides improved resolution, high absolute‐energy levels, and excellent reliability.

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