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2018 AAPG International Conference and Exhibition

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Distributed Crestal Leakage:Evidence for Geologically Instantaneous (Catastrophic) Top Seal Failure

Abstract

Using a combination of three-dimensional seismic and well data, we show the evidence of a kilometer-scale gas leakage phenomena from the North West Shelf of Australia. The leakage exhibits at the seabed 522 horizontally clustered pockmarks covering an area of 100 km2 and comprises subsurface evidence of leakage, such as vertically stacked amplitude anomalies. The leakage structure is located above the Scarborough Gas Field, which we interpret as the source of gas. The leakage occurred in the Late Quaternary and emplaced in a geologically instantaneous catastrophic event. We analyzed the relationship between the gas water contact and the trap of the Scarborough Gas Field with respect to the position and the extent of the leakage above. We propose that the leakage structure, which we argue to be the result of the scattering of seal by-pass, is consistent to overpressure in the reservoir produced by an externally developed overpressure. We introduce a new mechanism of seal by-pass namely, Distributed Crestal Leakage, and a new parameter to characterized leakage above top seals.