A gas well that has dropped below its critical rate does not announce it. The rate sags, the line pressure wanders, somebody blames the reservoir, and the liquid column keeps growing until the well dies with reserves still in the ground. This works out the Turner and Coleman critical rates at the wellhead and tells you in plain words whether the well is unloading itself, marginal, or loading up — in the time it takes to read a gauge.
One-time purchase. No subscription. No account. Works offline at the wellsite.
A loading well and a depleting well draw the same falling line. One needs a velocity string or a plunger this month; the other needs nothing. Guess wrong and you either spend money you did not need to, or lose a well you could have saved.
Turner's equation lives in a workbook somebody built in 2009, with a hard-coded tubing ID and a z factor that has not been looked at since. Nobody remembers whether it was the adjusted coefficient or the raw one.
You know two of them are in trouble. You do not know which two. Working them out one at a time on the truck bonnet is how the marginal ones get missed until they stop flowing altogether.
Both correlations run at once. Turner is the conservative screen; Coleman fits the low-pressure wells below roughly 500 psi at the wellhead. The app shows both, says which one applies at your pressure, and gives you the percentage margin to each — so you know not just whether the well is lifting, but by how much, and how close it is to the edge.
Above the Turner rate it is unloading. Between the two it is marginal, lifting some of the time and slugging the rest. Below the Coleman rate it is loading up, and the calculator says so in those words rather than leaving you to compare two figures on a phone screen in the wind.
Flowing pressure in psig, wellhead temperature, gas gravity and z factor. The defaults (0.65 and 0.9) are the ones you would have used anyway.
2-3/8", 2-7/8" or 3-1/2" EUE from the list, or type a manual ID. Water or condensate — the surface tension and density come with it.
Turner and Coleman side by side, the margin to each, and a note saying which correlation to trust at your wellhead pressure.
Add each well to the screening table. It sorts by margin, so the well closest to loading up is at the top. Export to CSV for the morning report.
This is a wellhead droplet-model screen for vertical and near-vertical wellbores. Deviated and horizontal sections, tapered strings, downhole restrictions, foamers and plunger cycles are not modelled, and the app says so on screen rather than quietly giving you a number. Every formula is printed on the page with its coefficients, and a worked textbook example (2-3/8" EUE at 500 psia, 120 °F, water → Turner 743 Mscf/d, Coleman 619 Mscf/d) sits in the app so you can confirm it agrees with the book before you trust it on a well. It is an engineering screen against published correlations, not a nodal analysis.
Built by people who have worked the lease. Oil Rigs Now has been making tools for oilfield professionals since 2011 — field-first, offline-first, and priced so a pumper can expense it without asking anyone.
Everything stays on your device. Nothing is uploaded, no account is created, and the calculator keeps working when the lease road has no bars.