Sweetness

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Sweetness is a composite seismic attribute used to highlight thick, clean reservoirs, along with hydrocarbons contained within. Sweetness is calculated by dividing the instantaneous amplitude (amplitude envelope) by the square root of the instantaneous frequency. It can be used independently or corendered with other attributes.

History

Burnet Oliveros and her colleague Barbara Radovich adopted the techniques of generating pseudo-color[1] satellite images and applied them to the variety of seismic attributes that had been discovered in the years leading up to the early 1990's while working for Texaco's Exploration and Production Technology department. These pseudo-color techniques create combination displays that are both more informative and more concise than traditional display methods[2] . Oliveros based her displays around the two basic attributes of instantaneous amplitude and instantaneous phase. Trio, Duo, and Likeness are other examples of combination displays credited to Oliveros. She found that using sweetness, higher frequency events were devalued, and low frequency events were highlighted, ex. large, homogenous sand bodies.

Terminology

To determine sweetness, you must first understand several other seismic attributes, and how they relate to the Sweetness display:

  • Seismic: The ordinary seismic values shown in a display.
  • Seismic data from offshore Australia.

  • Instantaneous Amplitude: Also known as the Envelope. It is the magnitude of each pair of polar values produced by applying a Hilbert transformation to the original seismic trace[2]. The value for Amplitude is independent of phase. Higher amplitude events are often associated with changes in lithology, or act as direct hydrocarbon indicators.
  • Instantaneous Amplitude for the offshore Australia seismic data. Red = Higher Amplitude, Blue = Lower Amplitude

  • Instantaneous Phase: The angular part of each pair of polar values produced by applying a Hilbert transformation to the original seismic trace and is independent of the reflection strength.[3]
  • Instantaneous Phase for Offshore Australia. Blue = Troughs, Black = Peaks

  • Instantaneous Frequency: The vertical derivative of phase. In other words, how the phase changes each time step.
  • Instantaneous Frequency for the same section of offshore Australia seismic data. Red = Higher Frequency, Blue = Lower Frequency

Different combinations of these attributes create Oliveros' combination displays.

Uses of Sweetness

The value in the sweetness display is that it will reduce the contribution of high frequency events to your display. Areas containing higher amplitudes and lower frequencies (sandy intervals) will display the highest values for sweetness, while lower amplitude and higher frequency sediments (thinly bedded shales) will show lower values for sweetness. This combination display is useful for identifying gas stores (as seen in the red box in the image below), hydrates, and the top, flank, and base of Salt bodies. All of these features will show high sweetness values due to their higher amplitude values.

Bruce Hart was able to use sweetness in combination (corendered) with the coherence attribute to define channels, along with their probable infill[4]. In his work, Hart was able to better resolve channels in the corendered sweetness and coherence views when compared to amplitude alone. He was also able to better differentiate between different lithologies contained within the channels, due to the differences in sweetness observed.

References

  1. [1] False color Retrieved from https://en.wikipedia.org/wiki/False_color
  2. 2.0 2.1 Radovich, B. J., and R. B. Oliveros, 1998, 3-D sequence interpretation of seismic instantaneous attributes from the Gorgon field: The Leading Edge, v. 17, p. 1286–1293.
  3. R. Burnet Oliveros and Barbara J. Radovich (1997) Image‐processing display techniques applied to seismic instantaneous attributes over the Gorgon gas field, North West Shelf, Australia. SEG Technical Program Expanded Abstracts 1997: pp. 2064-2067.
  4. Hart, B. S. (2008). Channel detection in 3-D seismic data using sweetness. AAPG Bulletin, 92(6), 733-742. 

External Links

Hilbert Transform Information Churning seismic attributes with principal component analysis