What it is
A pre-seismic survey is any pre-drill subsurface characterization method deployed before a formal seismic acquisition program. The goal is to screen prospects so that the seismic program that follows is smaller, more focused, and more likely to be commercially worthwhile.
Pre-seismic surveys are not a new concept — regional gravity and magnetic surveys, for example, have been used as pre-seismic tools for decades. What's changed over the last ten years is the availability of pre-seismic methods that directly classify substance (hydrocarbons, specific minerals) rather than just structure. Remote NMR subsurface mapping is the most significant example in commercial use today.
Why it matters
The economic case for pre-seismic screening is straightforward: seismic acquisition is expensive (low seven figures USD onshore, mid-seven to mid-eight figures offshore), slow (6-18 months from acquisition decision to interpreted deliverable), and environmentally intrusive (crew access, vessel time, airgun emissions). A pre-seismic survey that costs 10-20% of a seismic program and runs 4-8 weeks can meaningfully reduce the scope of required seismic — typical 2-3× reduction in vessel days or crew weeks — or rule out prospects entirely before seismic commitment.
Common methods used as pre-seismic
- Remote NMR mapping — substance classification, full block-scale coverage
- Gravity and gravity gradiometry — structural screening, density anomalies
- Magnetotellurics — deep resistivity structure, useful for sub-salt and sub-basalt plays
- CSEM — offshore hydrocarbon screening via resistivity contrasts
- Satellite remote sensing — surface signatures that correlate with subsurface composition