Five reservoir fluids • Black oil: • GOR of 2000 scf/STB or less. • stock tank oil gravity is usually below 45º API. • stock tank oil is dark indicating of presence heavy hydrocarbons. • Color is often black or brown.
Exercise 1: • The reported production from the discovery well of the Nancy Field is given below. How would you classify this reservoir fluid?
Five reservoir fluids • Volatile oil: • Initial gas-oil ratios between 2000-3300 scf/STB. • Stock-tank oil gravity is usually 40 ºAPI or more. • Stock tank color is brown ,orange or green. • Oil formation volume factor is usually greater than 2.0 res bbl/STB. • Retrograde Gas: • Initial gas-oil ratio is more than 3300scf/STB up. • Practically gas-oil ratios more than 50000 scf/STB are usually treated as wet gases. • Stock-tank oil gravity is between 40 ºAPI and 60 ºAPI. • Liquid can be lightly colored, brown, orange greenish or water-white.
Five reservoir fluids • Wet gas: A wet gas exists solely as a gas in the reservoir throughout the reduction in reservoir pressure. Produced stock tank liquid gravity is the same as retrograde gas however it doesn’t change during the life of the reservoir. • Dry Gas: is simply methane with some intermediates. No liquid is formed at the surface.
Exercise 2: • The annual production statistics for west Oakvale field are given. Classify the reservoir fluid.
Exercise 3: • Laboratory analysis of a reservoir sample is given. The sample was obtained from the reservoir at 184 F and 3463 psig. • Plot the formation volume factor and solution gas oil ratio.
Coefficient of Isothermal compressibility • The coefficient of isothermal compressibility is defined as the fractional change of volume as pressure is changed at constant temperature. • Ideal gases: • Real gases: