Abstract

In the shallower regions of the 3D Nimitz seismic survey, there exist multiple interesting bright seismic amplitude anomalies. These anomalies, or funny looking things, occur in a confined spatial and temporal region of the seismic. They have a concave-up seismic appearance along the cross section. Bright seismic amplitudes can be a direct hydrocarbon indicator, or they can be representative of strong lithologic contrasts and/or acquisition artifacts. We have set out to investigate misinterpreted seismic anomalies along cross-sectional lines. Therefore, we apply seismic attributes to indicate that these bright spot features, which we interpret to be submarine gullies looking along time-slice intersections, can possibly be mistaken for hydrocarbon anomalies in a cross-sectional view. However, we cannot fully rule out the presence of hydrocarbons because it is common for gas sands to create similar anomalies. Previously drilled wells within the survey (Korimako-1 and Tarapunga-1) point to a lack of hydrocarbon potential in the subsurface. Although it is possible that these bright spots are due to hydrocarbon presence, we develop a more likely hypothesis: The lithology of the interfluve sediments is similar to the gully-margin drapes but differs from the gully sediment fill.

     
  • Funny looking thing (FLT):

    Submarine gullies

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  • Seismic appearance:

    High-amplitude spotted features

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  • Alternative interpretations:

    Lithologic anomalies, gas seeps, bright spots

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  • Features with a similar appearance:

    Gas accumulation, sediment fills in limestone paleocaves

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  • Formation:

    Giant Foresets Formation

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  • Age:

    Pleistocene

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  • Location:

    Taranaki Basin, New Zealand

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  • Seismic data:

    Nimitz 3D (cropped volume)

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  • Analysis tools:

    Curvature, instantaneous frequency, and sweetness attributes; well reports

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