Vertical anomaly clusters: Evidence for vertical gas migration across multilayered sealing sequences
Vertical anomaly clusters: Evidence for vertical gas migration across multilayered sealing sequences
We present the results of a seismic interpretational study of amplitude anomalies in the East Falkland basin using an extensive grid of approximately 8000 line kilometers (4971 line miles) of high-resolution two-dimensional seismic reflection data. We mapped 474 discrete amplitude anomalies developed within a dominantly hemipelagic and highly reflective megasequence of the Cretaceous to early Cenozoic that is distributed in a northeast–southwest swath across the basin. The amplitude anomalies range from a kilometer to over 25 km (15.5 mi) in lateral extent, have sharp lateral amplitude cutoffs, sometimes at faulted margins, and are invariably associated with reflections with negative acoustic impedance contrasts. They exhibit class III amplitude versus offset (AVO) responses, frequency shadows, and push-down effects, from which the amplitude anomalies are interpreted as related to free gas. All the amplitude anomalies are characterized by vertical clustering, and based on this strong spatial association we refer to these mappable groups of amplitude anomalies as vertical anomaly clusters (VACs). We suggest that VACs form by strongly focused vertical hydrocarbon migration in a heterogeneous stacked sequence of poor-quality reservoirs interbedded with layers with lower permeability, and where the necessary bottom-to-top cross-stratal flow exploits a well-developed fault and fracture network. Similar vertical associations of gas-related amplitude anomalies could be expected in many other basins, so VACs may be a useful direct hydrocarbon indicator with specific genetic significance for hydrocarbon migration mechanisms.
1859-1884
Foschi, Martino
bbe09b05-772a-4abb-8449-0bc5a2ceeb05
Cartwright, Joseph A.
90642e11-daa1-43dc-8a3b-3d04976f4272
Peel, Frank J.
ccbb86f8-56a0-4b59-b664-e772a9c4015f
September 2014
Foschi, Martino
bbe09b05-772a-4abb-8449-0bc5a2ceeb05
Cartwright, Joseph A.
90642e11-daa1-43dc-8a3b-3d04976f4272
Peel, Frank J.
ccbb86f8-56a0-4b59-b664-e772a9c4015f
Foschi, Martino, Cartwright, Joseph A. and Peel, Frank J.
(2014)
Vertical anomaly clusters: Evidence for vertical gas migration across multilayered sealing sequences.
AAPG Bulletin, 98 (9), .
(doi:10.1306/04051413121).
Abstract
We present the results of a seismic interpretational study of amplitude anomalies in the East Falkland basin using an extensive grid of approximately 8000 line kilometers (4971 line miles) of high-resolution two-dimensional seismic reflection data. We mapped 474 discrete amplitude anomalies developed within a dominantly hemipelagic and highly reflective megasequence of the Cretaceous to early Cenozoic that is distributed in a northeast–southwest swath across the basin. The amplitude anomalies range from a kilometer to over 25 km (15.5 mi) in lateral extent, have sharp lateral amplitude cutoffs, sometimes at faulted margins, and are invariably associated with reflections with negative acoustic impedance contrasts. They exhibit class III amplitude versus offset (AVO) responses, frequency shadows, and push-down effects, from which the amplitude anomalies are interpreted as related to free gas. All the amplitude anomalies are characterized by vertical clustering, and based on this strong spatial association we refer to these mappable groups of amplitude anomalies as vertical anomaly clusters (VACs). We suggest that VACs form by strongly focused vertical hydrocarbon migration in a heterogeneous stacked sequence of poor-quality reservoirs interbedded with layers with lower permeability, and where the necessary bottom-to-top cross-stratal flow exploits a well-developed fault and fracture network. Similar vertical associations of gas-related amplitude anomalies could be expected in many other basins, so VACs may be a useful direct hydrocarbon indicator with specific genetic significance for hydrocarbon migration mechanisms.
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Published date: September 2014
Organisations:
Marine Geoscience
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Local EPrints ID: 370706
URI: http://eprints.soton.ac.uk/id/eprint/370706
ISSN: 0149-1423
PURE UUID: 39e8e34b-b48e-42aa-b707-44e1c6412580
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Date deposited: 05 Nov 2014 10:33
Last modified: 14 Mar 2024 18:20
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Author:
Martino Foschi
Author:
Joseph A. Cartwright
Author:
Frank J. Peel
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