GOR (Gas-Oil Ratio) is the ratio of gas produced to oil produced from a well, measured in standard cubic feet of gas per stock tank barrel of oil (scf/STB). It is one of the most important parameters in reservoir engineering and production operations, providing insight into reservoir pressure, fluid behavior, and depletion status. A typical Permian Basin oil well may start with a GOR of 800 to 2,000 scf/STB, while a volatile oil reservoir can produce at 3,000 to 8,000 scf/STB. Gas-condensate reservoirs exhibit GOR values of 8,000 to 70,000 scf/STB, and dry gas wells produce at effectively infinite GOR.
How It Works
Understanding GOR requires knowledge of how hydrocarbons exist in the reservoir and change as they travel to surface:
- Solution Gas (Rs) — At reservoir pressure and temperature, gas is dissolved in the oil like carbon dioxide in a sealed soft drink. The amount of dissolved gas is described by the solution GOR, which depends on pressure, temperature, and fluid composition. Typical solution GOR ranges from 200 to 2,000 scf/STB.
- Bubble Point Pressure — The pressure at which dissolved gas begins to come out of solution and form free gas bubbles. When reservoir pressure drops below the bubble point, free gas appears in the formation and the producing GOR begins to change.
- Producing GOR Behavior — Below the bubble point, the producing GOR initially stays relatively constant, then increases sharply as the gas-to-oil mobility ratio increases with pressure depletion. A rapidly rising GOR is a classic indicator of pressure depletion and reservoir drive inefficiency.
- Measurement — GOR is calculated from periodic well tests where oil and gas rates are measured separately through a test separator. Oil rate is measured in stock tank barrels per day (STBD) and gas rate in thousands of standard cubic feet per day (Mscf/d).
Key GOR categories and their implications:
- Low GOR (< 500 scf/STB) — Heavy oil or undersaturated reservoirs. Indicates strong water drive or early-life production above bubble point.
- Moderate GOR (500-2,000 scf/STB) — Typical black oil reservoir. Most common in conventional and unconventional oil plays.
- High GOR (2,000-8,000 scf/STB) — Volatile oil or gas-condensate transition. Requires careful separator optimization and gas handling.
- Very High GOR (> 8,000 scf/STB) — Gas-condensate or wet gas. Economics often driven by gas and NGL revenue rather than oil.
Why It Matters
GOR directly impacts artificial lift selection, surface facility design, and economics. Wells with GOR above 1,500 scf/STB are poor candidates for ESPs (gas causes cavitation and pump damage) and better suited for gas lift or plunger lift systems. Surface separators, compressors, and gas handling equipment must be sized for peak GOR, which may be 3 to 5 times initial GOR as the reservoir depletes. From an economics perspective, associated gas revenue can represent 20 to 40% of total well revenue in high-GOR plays, making accurate GOR measurement essential for production forecasting and reserves estimation.
How Netora Handles GOR Tracking
Netora E&P Production automatically calculates GOR from well test data and tracks its evolution over time for every well. The platform flags significant GOR changes that may indicate reservoir or completion problems — such as a sudden GOR spike suggesting casing or packer failure — and provides GOR data as an input to artificial lift optimization and decline curve analysis. Learn more about Netora E&P Production.