1. 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 = 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 = ρ o ρ w

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

γ oT = γ o 1+0.465791x 10 −3 (T−60)

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

γ API = 141.5 γ O −131.5

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

γ ob =( γ o +2.18x 10 −4 R s γ g )/ B ob

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 c ¯ o (P− P b )

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