- 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.

$${\rho}_{\text{o}}=\frac{{m}_{o}}{{v}_{o}}$$The relative density of oil is defined as the ratio of the density of the oil to that of water usually at 60 oF.

$${\gamma}_{\text{o}}=\frac{{\rho}_{o}}{{\rho}_{w}}$$The relative density of oil at any other temperature T can be calculated using

$${\gamma}_{oT}=\frac{{\gamma}_{o}}{1+0.465791x{10}^{-3}(T-60)}$$In the petroleum industry, it is common to express oil density in terms of oil API gravity, or:

$${\gamma}_{API}=\frac{141.5}{{\gamma}_{O}}-131.5$$An equation for oil relative density at bubblepoint pressure (Pb) is expressed as

$${\gamma}_{ob}=({\gamma}_{o}+2.18x{10}^{-4}{R}_{s}{\gamma}_{g})/{B}_{ob}$$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

$${\gamma}_{\text{op}}={\gamma}_{\text{ob}}{\text{e}}^{{\overline{\text{c}}}_{\text{o}}\text{(P}-{\text{P}}_{\text{b}}\text{)}}$$Correlation for calculating average oil compressibility Co at various conditions is presented later.