Prospect Evaluation and Volumetrics
A prospect is a closed contour until you can defend the barrels inside it. You will read traps and stratigraphic plays off the seismic, turn rock into net pay and STOIIP in the well, then do the honest part: ranges, tornado charts, and the decision they feed.
You can identify and frame a trap on 3D seismic, read the stratigraphic play behind it, set cutoffs and compute net pay and STOIIP you can defend, replace the single number with a P10-P90 range from Monte Carlo, rank the inputs on a tornado chart, and state the drill, appraise, or drop case against the petroleum system.
The prospect on the map
You cannot name a trap until you can name the regime that built it, and every fault bounding your prospect is either a seal or a leak point; throw and juxtaposition decide which.
Most four-way closures were built by folding or by salt; know the mechanism and you know where the crest, the flank, and the trouble will be.
The spill point sets the maximum closure and therefore the maximum case; prospect identification is the discipline of proving a container before you argue about its contents.
A prospect drawn on one line is an opinion; picks only become a container when horizons and faults close consistently in 3D, and the framework is where that gets proven or exposed.
The trap holds nothing without a reservoir inside; sequence stratigraphy and depositional systems tell you which interval could be sand and why it got there.
Channels and fans are the reservoirs of the stratigraphic trap, and seismic geomorphology is how you catch them in plan view instead of hoping on a single line.
Rock to barrels
Net pay is where petrophysics turns into money; every cutoff quietly moves the barrels, so know what each threshold keeps and what it throws away.
STOIIP is a handful of measured quantities multiplied together; the equation is trivial and the inputs are the whole argument.
A cutoff nobody stress-tested is a liability in the reserves audit; sensitivity is how you learn whether the pay is robust or an artifact of one threshold.
Ranges, not numbers
GRV is usually the biggest lever in the whole volumetric stack, and it is set by two things you drew yourself: the top structure map and the contact.
The single best estimate is the first casualty of the first well; carrying distributions through the equation is how a prospect states what it honestly does not know.
The tornado chart is the cheapest appraisal plan you will ever make: it says which uncertainty is worth money to shrink and which is noise.
The decision
Volumetrics assumes charge; the petroleum system checklist, source, migration, reservoir, seal, trap, and timing, is the part of the case no map can prove on its own.
Cores, logs, seismic, and tests each see the reservoir at a different scale; a drillable case knows which claims rest on which data, and what remains a guess.
Every prospect decision is a conceptual model wearing numbers; assembling one from partial data, and saying what would change your mind, is the whole job in miniature.