Free oil, gas and refinery calculators
17 everyday calculations for production, terminals and refineries: properties, tank gauging, separation, gas and heaters. Formula and practice for each.
Properties and blending
API gravity, specific gravity and density
The higher the API gravity, the lighter the product. Water = 10 °API; light crude > 31.1 °API; heavy crude < 22.3 °API. 60 °F = 15.56 °C.
Kinematic ↔ dynamic viscosity
Take ν and ρ at the same temperature: an oil's viscosity can double for 10 to 15 °C less.
Blend viscosity (Refutas method)
Both viscosities must be at the same temperature (often 50 °C for fuel oils). Empirical method: confirm the blend in the lab.
Two-product blend (density, sulfur)
Sulfur blends by mass, density by volume (ideal mixing, no shrinkage). For a tight specification keep a margin and test the blend.
Tank gauging and measurement
Vertical tank: volume from level
Ideal cylinder. For custody transfer use the tank's strapping table and subtract the dead bottom.
Horizontal tank: partial volume
Cylindrical shell only (flat ends). Dished heads add volume: use the manufacturer's table for accounting.
Volume correction to 15 °C
Simplified method (ASTM D1250-80 Table 54A/B/D equation, no pressure correction): for training and checks, not for invoicing, which follows the full API MPMS 11.1.
BS&W and net oil volume
Common pipeline crude specification: 0.5 % (sometimes 1 %). BS&W is measured by centrifuge; water alone by Karl Fischer or distillation.
Flow conversion: bbl/d, m³/h, t/d
1 US barrel = 42 US gallons = 158.987 L. Use the density at the temperature the volume refers to (often 15 °C).
Production, separation and gas
Water cut and gas-oil ratio
Rates at stock-tank conditions (oil at 15 °C, gas in Sm³ at 15 °C and 101.325 kPa). 1 Sm³/m³ ≈ 5.615 scf/bbl. A rising GOR can mean an advancing gas cap.
Horizontal separator: liquid retention time
Common guide: 1 to 3 min for a two-phase separator on light crude, 3 to 10 min or more for three-phase service or heavy or foaming crude. Heads not counted.
Gas flow at standard conditions
Atmospheric pressure taken as 101.325 kPa. Z comes from a correlation or an AGA 8 calculation; Z = 1 for low-pressure gas.
Gas specific gravity from molar mass
Methane = 16.04 g/mol (SG 0.554); typical dry natural gas 17 to 20 g/mol. M comes from the gas chromatograph analysis (Σ yᵢ Mᵢ).
Pipeline: velocity, Reynolds number and throughput
Re < 2000: laminar flow; > 4000: turbulent. Usual velocities in liquid lines: 1 to 3 m/s.
Refining and re-refining
Fired heater: duty and efficiency
Sensible heat only: if the charge partly vaporises (crude heater), use enthalpies instead. Typical efficiency on LHV: 80 to 92 %.
Distillation cut yields and mass balance
Use mass flows over the same period. A closure outside 98 to 102 % points to a meter, a density or a tank level to check.
Used-oil re-refining: base-oil yield
Order of magnitude: 60 to 75 % base oil on dry used oil; the rest becomes light fuel, gas oil and an asphalt-like residue. Water is measured by distillation.
Learning and checking tools. The ranges shown are general guidance: always follow your plant's procedures, permits and set points. Nothing is sent anywhere: the calculations run in your browser.
The same maths, with a plant that reacts: the Beedy simulators.