To find the gas density:

To find downhole density:

## Petroleum Engineering Equations & Formulas

#### Oil density

Oil density at surface conditions is commonly quoted in °API.

#### Formula:

       API = 141.5/γo-131.5

Where:

γo is the specific gravity of oil (relative to water = 1, measured at STP).



The downhole density of oil (at reservoir conditions) can be calculated from the surface density equation using:

       ρorc * Bo = ρo + Rs * ρg

Where:

ρorc : is oil density at reservoir conditions (kg/m3)

Bo   : is the oil formation volume factor     (rm3/stm3)

ρo   : is oil density at standard conditions  (kg/m3)

Rs   : is the solution gas : oil ratio        (sm3/stm3)

ρg   : is gas density at standard conditions  (kg/m3)



### $$API = \frac{141.5}{\gamma_{o}} - 131.5$$

Where:

• $\gamma_{o}$ is the specific gravity of oil (relative to water = 1, measured at STP).

### $$\rho_{orc}*B_{o} = \rho_{o} + R_{s} * \rho_{g}$$

Where:

• $\rho_{orc}$ is the oil density at reservoir conditions $(kg/m^{3})$
• $B_{o}$ is the oil formation volume factor $(rm^{3}/stm^{3})$
• $\rho_{o}$ is the oil density at standard conditions $(kg/m^{3})$
• $R_{s}$ is the solution gas : oil ratio $(sm^{3}/stm^{3})$
• $\rho_{orc}$ is the gas density at standard conditions $(kg/m^{3})$