Permanent Reservoir Monitoring (PRM)

Part 7 — Special geometries

Learning objectives

Describe PRM and its repeatability advantage over streamer 4D
Quote typical NRMS numbers: streamer 4D 30–50% vs PRM 5–15%
List major PRM installations (Valhall, Ekofisk, Atlantis)
Describe the economics of PRM vs streamer time-lapse

Permanent Reservoir Monitoring (PRM) installs receivers permanently on the seabed over a producing field — trenched fibre, seabed cables, or buried geophone arrays. The source vessel shoots over the same receivers every few months, possibly indefinitely. Because the receivers never move, every repeat shoot uses the same recording geometry; repeatability — the limiting factor in 4D seismic — transforms.

Repeatability as a metric

The industry’s repeatability metric is Normalised RMS (NRMS): the RMS difference between baseline and monitor divided by the mean RMS, expressed as a percentage. Lower is better. Streamer 4D achieves NRMS 30–50% (streamer positions vary survey-to-survey, weather differs, source signature drifts). PRM achieves 5–15% (same nodes recording the same wavefield). That 3–10× reduction makes fluid-movement signatures that were buried in streamer-4D noise suddenly visible in PRM 4D.

Real-world installations

Valhall (BP, North Sea) — trenched fibre-optic cable installed 2003, monthly repeat surveys ever since, 20+ years of 4D. Ekofisk (ConocoPhillips) — OBC PRM enabled seafloor-compaction monitoring that directly informs platform-jack-up decisions. Atlantis (BP, Gulf of Mexico) — nodal PRM turned a salt-complex imaging nightmare into monthly-refreshed development support. Jubarte (Petrobras, Campos Basin) — early OBN PRM for pre-salt carbonate monitoring.

Economics

A PRM installation on a large field costs $50–200 M up-front (cables, trenching, connectors, permanent power). A streamer time-lapse survey over the same field costs$ 10–30 M per repeat. Break-even comes at 3–5 repeat surveys, but the real value is information-delivery cadence: PRM runs monthly, a streamer fleet runs every 2–3 years. Monthly-refreshed 4D supports production decisions (infill drilling, water-injection tuning, gas-cap management) that a two-yearly streamer schedule simply cannot.

References

Lumley, D. (2001). Time-lapse seismic reservoir monitoring. Geophysics, 66(1), 50–53.
Calvert, R. (2005). 4D technology: where are we, and where are we going? Geophysical Prospecting, 53(2), 161–171.
Berg, E., Svenning, B., Martin, J. (2010). OBN technology — recent developments. EAGE Workshop on Permanent Reservoir Monitoring.