About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract

AAPG Bulletin, V. 98, No. 9 (September 2014), P. 18591884.

Copyright copy2014. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/04051413121

Vertical anomaly clusters: Evidence for vertical gas migration across multilayered sealing sequences

Martino Foschi,1 Joseph A. Cartwright,2 and Frank J. Peel3

1 Cardiff University, 3DLab, Earth and Ocean Sciences School, Cardiff CF103YE, United Kingdom; present address: PDRA Shell Geoscience Laboratory, Department of Earth Sciences University of Oxford, South Parks Road, Oxford, OX1 3AN, United Kingdom; [email protected]
2 University of Oxford, Department of Earth Sciences, Oxford OX1 3AN, United Kingdom; [email protected]
3 BHP Billiton Petroleum, 1360 Post Oak Boulevard, Houston, Texas 77560; [email protected]

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.

Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Watermarked PDF Document: $14
Open PDF Document: $24

AAPG Member?

Please login with your Member username and password.

Members of AAPG receive access to the full AAPG Bulletin Archives as part of their membership. For more information, contact the AAPG Membership Department at [email protected].