Time-Lapse: Monitor a Producing Field
The reservoir moves; learn to watch it. Rock physics of change, acquisition built for repeatability, processing that protects the difference, and the case files where 4D earned its keep.
You can say which reservoir changes are seismically visible and why, specify what a monitor survey must repeat, read an NRMS map without flinching, and interpret a 4D difference with Valhall and Sleipner as your reference points.
Why production changes the seismic
4D is impedance arithmetic done twice and subtracted; the baseline physics has to be reflex before the difference means anything.
Fluid substitution is the forward model of every time-lapse anomaly you will ever interpret; run it before you believe anything.
Time-lapse pays only when the production-induced impedance change clears the repeatability noise; feasibility is a number computed before the survey, not a hope after it.
Depletion moves stress as well as fluid: the minimum stress falls along the stress path at about two thirds of the depletion, the reservoir compacts, and the strained overburden writes time-shifts that fluid alone cannot explain.
A compacting reservoir strains the rock above it, and the Hatchell-Bourne R-factor turns that strain into overburden time-shifts: a 4D signal with no fluid in it at all, loudest over soft chalk.
Acquire for repeatability
A 4D signal is small by construction; signal-to-noise budgets decide whether your monitor survey can even see it.
Sensors cemented in place make repeatability a property of the installation instead of a hope; PRM is 4D taken seriously.
Fiber turns every well into a permanent receiver array; gauge length and Rayleigh scatter are the physics of that bargain.
Process the difference
Two surveys shot years apart only subtract cleanly after binning and matching filters make them the same experiment.
NRMS is the honesty metric of time-lapse; learn what good looks like so nobody can sell you noise as signal.
Processing vintages together instead of separately turns repeatability from an accident into a design objective.
Interpret the difference
Hardening here, softening there: a difference volume is a map of what the field did since baseline, if you read it with the rock physics attached.
Storage turns monitoring from optimization into obligation; the plume must be seen, bounded, and reported for decades.
Case files
Compaction, subsidence, and a life-of-field seismic system: Valhall seen from the interpretation chair and the acquisition barge at once.
The budget alternative to PRM: what repeated towed-streamer 4D can and cannot promise, in a basin that tried everything.
The first industrial CO2 store and the longest-running public 4D story; every storage project argues with Sleipner first.
One dataset, every lesson: push a marginal 4D signal through matching, metrics, and interpretation without fooling yourself.