Hydrocarbon indicator

A hydrocarbon indicator (HCI) or direct hydrocarbon indicator (DHI), is an anomalous seismic attribute value or pattern that could be explained by the presence of hydrocarbons in a oil or gas reservoir.

DHIs are particularly useful in hydrocarbon exploration for reducing the geological risk of exploration wells. Broadly, geophysicists recognize several types of DHI:

• Bright spots: localized amplitudes of greater magnitude than background amplitude values. Equipment prior to the 1970s had the bright spots obscured due to the automatic gain control.^[1]
• Flat spots: nearly horizontal reflectors that cross existing stratigraphy, possibly indicating a hydrocarbon fluid level within an oil or gas reservoir.
• Dim spots: low amplitude anomalies.^[2]
• Polarity reversals can occur where the capping rock has a slightly lower seismic velocity than the reservoir and the reflection has its sign reversed.^[1]

Some geoscientists regard amplitude versus offset anomalies as a type of direct hydrocarbon indicator. For example, the amplitude of a reflection might increase with the angle of incidence, a possible indicator of natural gas.^[1]

See also

• Amplitude versus offset

References

1. Sheriff, Robert E.; Geldart, Lloyd P (1995). "10.8". Exploration Seismology (2 ed.). pp. 415–418. ISBN 0521468264.
2. M. Bacon; R. Simm; T. Redshaw (2007). 3-D Seismic Interpretation. Cambridge: Cambridge University Press. ISBN 978-0-521-71066-4.