DHI Evidence Checklist

Systematically evaluate Direct Hydrocarbon Indicator (DHI) evidence from seismic data. Score your observations across amplitude, AVO, and structural criteria to assess hydrocarbon risk and confidence. Based on industry best practices.

DHI Bright Spot Flat Spot Risk Assessment

DHI Evaluation Criteria

1. Amplitude Evidence (25 points)

Significantly brighter or dimmer than background

Follows structural dip, not stratigraphy

Horizontal reflection cutting structure (fluid contact)

Top bright (gas-over-brine), base dim or reversed

2. AVO Evidence (30 points)

Negative intercept, negative gradient (classic gas sand)

Brightens on far angles (Classes 2, 3)

Negative fluid factor (below G = R₀ trend)

AVO anomaly follows amplitude anomaly updip

3. Structural/Stratigraphic (20 points)

4-way dip closure or stratigraphic trap

Anomaly does not extend beyond spill point

Shale/mudstone above reservoir with adequate thickness

4. Supporting Evidence (15 points)

Deeper reflectors pulled down (low velocity gas)

Hard event becomes soft (or vice versa)

Nearby wells show gas effect or similar lithology

5. Negative Indicators (Subtract Points)

Likely stratigraphic, not fluid

Amplitude constant with angle (not fluid)

Low S/N, acquisition footprint, processing artifacts

Wrong depth, missing source/migration pathway

Assessment Results

DHI Background & References

What are DHIs?

Direct Hydrocarbon Indicators (DHIs) are seismic attributes that directly suggest the presence of hydrocarbons:

  • Bright spots: High-amplitude reflections from gas-brine contact
  • Flat spots: Horizontal fluid contacts cutting structure
  • AVO anomalies: Amplitude increasing with offset (gas effect)
  • Dim spots: Low amplitude from oil-water contact
  • Polarity reversals: Phase change at fluid contact

Pitfalls & False Positives

  • Stratigraphic brightening: Lithology changes can mimic gas
  • Tuning effects: Thin beds create amplitude anomalies
  • Processing artifacts: Acquisition footprint, multiples
  • Poor data quality: Noise can mask or mimic DHIs

⚠ Always integrate with geology, well control, and regional understanding.