Restec

Oil Density

Oil density is required at various pressures and temperatures for reservoir and production engineering calculations. The oil density is defined as the mass per unit volume at a specified pressure and temperature.

ρ_{o} = \frac{m_{o}}{v_{o}}

The relative density of oil is defined as the ratio of the density of the oil to that of water usually at 60 oF.

γ_{o} = \frac{ρ_{o}}{ρ_{w}}

The relative density of oil at any other temperature T can be calculated using

γ_{o T} = \frac{γ_{o}}{1 + 0.465791 x 10^{- 3} (T - 60)}

In the petroleum industry, it is common to express oil density in terms of oil API gravity, or:

γ_{A P I} = \frac{141.5}{γ_{O}} - 131.5

An equation for oil relative density at bubblepoint pressure (Pb) is expressed as

γ_{o b} = (γ_{o} + 2.18 x 10^{- 4} R_{s} γ_{g}) / B_{o b}

Above bubblepoint pressure, increased pressure will compress the liquid and increase its density. For the case of P > Pb, the oil relative density at P is calculated from

γ_{op} = γ_{ob} e^{{\bar{c}}_{o} (P - P_{b})}

Correlation for calculating average oil compressibility Co at various conditions is presented later.