Ice Scours as Trapping Mechanism for Shallow Gas

Haavik, Kjetil Eik; Landrø, Martin

doi:10.3997/2214-4609.20130004

Cited by 1 publication

(5 citation statements)

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“…6) have earlier been interpreted as a result of relict ploughmarks acting as a trapping mechanism for shallow gas (Haavik and Landrø, 2013). This trap is the result of icebergs that have plowed down in a sandy sea floor, followed by deposition of finer sediments that can act as a seal, or that the icebergs have plowed down in sand that lies beneath shale.…”

Section: Discussionmentioning

confidence: 96%

“…In this area shallow gas has been identified as vertical structures and chimneys on seismic reflection data in Paleogene and Neogene sediments over most of the known hydrocarbon reservoirs (D'Heur, 1987;Pekot and Gersab, 1987;Granli et al, 1999). Shallow gas in the Quaternary sediments has been identified within seismic (Lie and Larsen, 1991;Haavik and Landrø, 2013), and also encountered in several exploration wells drilled in this area (according to NPD Fact Pages (2014), wellbore 2/1-1, 2/4-13, 2/4-15 and 2/4-16). A major underground blow out took place when Saga Petroleum drilled the 2/4-14 well into a Jurassic reservoir in 1989.…”

Section: Historical Settingmentioning

confidence: 97%

“…Buried Iceberg ploughmarks in the North Sea were first reported by Stoker and Long (1984) and later by others (e.g. Graham et al, 2007;Kuhlmann and Wong, 2008;Dowdeswell and Ottesen, 2013;Haavik and Landrø, 2013). Identifying buried iceberg ploughmarks in seismic data is a much used method to determine whether or not the buried sediments are deposited during a period of glacial influence.…”

Section: Introductionmentioning

confidence: 97%

“…Shallow gas has been observed in association with buried iceberg ploughmarks in various ways (Gallagher and Heggland, 1994;Kuhlmann and Wong, 2008;Haavik and Landrø, 2013). Haavik and Landrø (2013) proposed a method for how iceberg ploughmarks act as a trapping mechanism for shallow gas in sand layers.…”

Section: Introductionmentioning

confidence: 99%

“…Haavik and Landrø (2013) proposed a method for how iceberg ploughmarks act as a trapping mechanism for shallow gas in sand layers. In this paper we describe this trap in more detail and the effect thin gas filled sand layers have on imaging of iceberg ploughmarks.…”

Section: Introductionmentioning

confidence: 99%

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Iceberg ploughmarks illuminated by shallow gas in the central North Sea

Haavik

Landrø

2014

Quaternary Science Reviews

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a b s t r a c tConventional 3D seismic data provides direct evidence for glacial influence during the early Pleistocene sedimentation in the Central North Sea. We identify iceberg ploughmarks as dim linear to curve-linear features in three early Pleistocene horizons that have high reflection amplitude compared to adjacent horizons. The anomalous horizons are interpreted to be reflections from thin sandy layers saturated with gas. The gas acts as a contrast liquid illuminating the thin sand layers. The reason for this is the difference in acoustic properties between water and gas saturated sand layers. The combination of thin bed effects and shallow gas makes the iceberg ploughmarks easily detectable as dim features in seismic reflection amplitude maps. Our interpretation is based on analysis of real seismic data, well logs and modeled seismic response. The methods we use include interpretation of horizons followed by extraction of reflection amplitudes, well log analysis, pre-stack amplitude versus offset analysis of high resolution 2D seismic data and time-lapse analysis of seismic. Seismic modeling is performed to study interactions between thin sand beds, shallow gas and iceberg ploughmarks. A new trapping mechanism for shallow gas is presented and seismic modeling of this trap strengthens our interpretation. The trap is created by iceberg ploughmarks in sandy layers that are covered by finer and less permeable sediments. For this area we find that conventional seismic interpretation is superior to the much used method of studying seismic time-slices for detection of iceberg ploughmarks, both with respect to time and detectability. This study shows that the interpreter should look for high amplitude horizons with amplitude variations laterally when trying to detect iceberg ploughmarks.

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Section: Discussionmentioning

confidence: 96%

Section: Historical Settingmentioning

confidence: 97%