Unlock Tight Rock
Nanodarcy rock holds decades of gas and will not give up a molecule on its own. Find the organic-rich interval, judge its maturity and its brittleness, then fracture it deliberately: the gradient that prices the job, the breakdown that starts it, the DFIT that measures what it did, and the frac hit that punishes anyone who forgets the field is connected.
You can screen a source rock for organic richness with Passey, place it in its maturity window, separate adsorbed from free gas, judge frac-ability from brittleness honestly, read a fracture gradient and a breakdown pressure from the stress model, interpret a DFIT for closure and leakoff, reason about what a frac at scale contacts, and explain a frac hit before it costs a parent well.
The prize in the tight rock
Nanodarcy matrix cannot feed a well; the stimulated volume around engineered fractures is the actual reservoir, and the steep decline is the small matrix blocks emptying into it.
Total organic carbon is the play's first filter, and the Passey delta-logR overlay reads it from ordinary logs, which is why a forty-year-old well can still screen a new play.
The same rock is a play or a disappointment depending on how long it cooked: vitrinite and the oil and gas windows decide what the organic matter became.
Half the gas can be stuck to the organic surfaces rather than compressed in the pores; the split decides both the volumes and how the rate declines late in life.
Quartz and carbonate take a frac, clay absorbs one; the mineralogical brittleness index is the screening tool that maps where completion dollars will actually buy fracture area.
Price the fracture
The pressure the rock fractures at is the least principal stress, and the honest spread between predicted and measured fracture gradients is the uncertainty every frac design carries.
The wall fails in tension at the breakdown pressure, then the fracture propagates at a lower steady pressure just above the minimum stress; the pressure record of a frac job is this physics written in real time.
The diagnostic fracture injection test is the tight-rock well's leak-off test: the closure pick on the G-function is the minimum stress, measured, and the leakoff signature is the reservoir introducing itself.
The Rickman elastic brittleness index is used everywhere and abused nearly as often; computing it and knowing what it does not measure is the difference between a screen and a superstition.
A multi-stage job is the fracture-gradient physics run dozens of times down a lateral; net pressure, contained height, and created area are what the treatment plot is actually saying.
The field answers back
Producing the parent well lowers its pore pressure and drags the minimum stress down along the stress path; the depleted zone becomes a low-stress magnet for every fracture pumped near it.
The child well's fracture grows asymmetrically toward the depleted parent and connects: the industry's most expensive lesson in stress-path physics, reproducible on one map.
The play elements assemble on one section: richness, maturity, gas in place, brittleness, and the completion verdict, the full screening workflow in miniature.
The Permian case file runs the whole path at basin scale: landing zones, stage spacing, and the completion design argument, with real-world economics keeping score.