An engineer watching a well doesn't just ask "how much oil is it making?" The more revealing question is often "how much gas is it making per barrel — and is that number moving?" The gas-oil ratio (GOR) is one of the cheapest diagnostics you have. You already report the oil and the gas every month. Dividing one by the other turns two production streams into a single curve that tracks what's happening thousands of feet down.
The question a real user asks is simple: "Is this well's GOR climbing, and how fast?" Everything downstream — reserve estimates, artificial-lift decisions, whether an offset is depleting the same pressure — hangs off the answer.
What GOR actually tells you
GOR is gas volume divided by oil volume, conventionally expressed in scf per barrel (mcf per barrel works fine for quick internal comparisons as long as you stay consistent). A stable GOR early in a well's life usually means you're producing above the bubble point on solution-gas drive — the gas stays dissolved and the ratio holds roughly flat.
When the ratio starts climbing, the reservoir is telling you something:
- Pressure has dropped below the bubble point. Gas breaks out of solution in the reservoir and flows preferentially, so you produce more gas per barrel of oil. This is the classic signature of a maturing solution-gas-drive reservoir.
- A gas cap is expanding or coning toward the perforations.
- Interference — an offset operator's production, or your own infill, is drawing down the same pressure.
A sudden GOR drop, by contrast, can flag a mechanical issue, a workover that restored oil rate, or liquid loading in a gassier completion. Either direction, the ratio moves before the oil rate tells the whole story.
Pulling the ratio from the record
You don't need a reservoir simulator to start. The full production history for a well lives in the record — monthly oil in barrels and monthly gas in mcf, from first production forward. Ask for both streams on the same well and compute the ratio month over month, and you have a GOR curve that spans the entire producing life of the wellbore.
Conversationally, that's a single question: "Show me the monthly oil, gas, and gas-oil ratio for this API since first production, and tell me whether the GOR trend is rising." The platform returns the series and the trend direction. What used to be an afternoon of exporting spreadsheets and wrestling with allocation is now the first thing you look at.
The same trend-analysis engine that measures decline rate and growth rate on a single stream applies cleanly to a ratio. You get a slope — how many scf/bbl per month the ratio is gaining — and you can tell the difference between noise and a real inflection.
Reading the shape
A few patterns are worth recognizing quickly:
- Flat, then a steady climb. The plateau is above-bubble-point production; the break is where reservoir pressure crossed below it. The timing of that break, compared against cumulative oil, is a rough read on how much of the reservoir energy you've spent.
- Early spike that settles. Common in the first few months of a horizontal — flowback and cleanup dominate before the well finds its true ratio. Don't over-read the first 60–90 days.
- A step change. A discrete jump in GOR that lines up with a workover date, a new nearby permit, or an offset's first production is usually mechanical or interference, not natural depletion. That distinction changes what you do about it.
The useful move is to put the well's GOR trend next to its offsets. If three neighboring wells all bend upward in the same quarter, you're looking at a field-wide pressure story, not a single-well problem. Benchmarking a well against its offsets and its county average is exactly the kind of comparison the data lake is built to answer, and applying it to GOR instead of raw rate gives you the reservoir view rather than the completion view.
Turning it into an action
A rising GOR is not automatically bad news — it's information you can price. If the ratio is climbing on natural depletion, it feeds directly into a lower remaining-oil expectation and helps you sanity-check a reserve number. If it's climbing because an offset came online, that's a competitive-drainage question worth watching permit filings around. If it stepped up right after a workover, you may have simply changed the well's flow regime.
Because the record updates as new production posts, you can set the ratio up as a watch item: flag the well when its GOR trend crosses from flat to rising, the same way you'd alert on an oil decline or a new permit nearby. That turns a lagging diagnostic into an early one — you see the drive mechanism shift while there's still time to act on lift, spacing, or a divestment decision.
The takeaway
Oil rate tells you what a well made last month. GOR tells you what the reservoir is becoming. Both streams are already in the record for every well; the value is in reading them together, spotting the inflection, and comparing it across offsets before the trend shows up in the check. Ask the ratio, not just the rate.