What it is
A direct hydrocarbon indicator (DHI) is a physical signal interpreted to indicate the presence of hydrocarbons themselves, as opposed to interpreting the structural geology that merely permits hydrocarbon accumulation. The canonical seismic DHIs include bright spots, dim spots, flat spots, phase reversals across fluid contacts, and amplitude-versus-offset (AVO) anomalies.
DHIs are not proofs of hydrocarbon presence. They are probabilistic indicators that, when present alongside a credible trap and seal, materially increase the pre-drill estimated probability of commercial success.
Why it matters
The fundamental problem in exploration is that structural imaging (where seismic excels) tells you where hydrocarbons could be, not where they are. DHIs provide the bridge between "structure present" and "substance likely present." Operators systematically use DHIs in prospect ranking and risk weighting.
Modern DHI sources
- Seismic-derived. Bright spots, flat spots, AVO, inversion attributes.
- Electromagnetic. CSEM resistivity anomalies, marine-CSEM hydrocarbon indicators.
- Remote substance classification. Inside Earth's remote NMR mapping returns direct substance classification, which is DHI-class information by a different physical route.
Common pitfalls
False-positive DHIs are common. Gas residuals, thin beds, lithology effects, and tuning artefacts can all mimic DHI responses. Robust pre-drill workflows require multiple independent DHI signals — ideally from different physical principles — before increasing prospect weightings.