Static oil pressure gradient estimation

Exploring for Oil and Gas Traps
Series	Treatise in Petroleum Geology
Part	Critical elements of the petroleum system
Chapter	Formation fluid pressure and its application
Author	Edward A. Beaumont, Forrest Fiedler
Link	Web page
Store	AAPG Store

The static oil pressure gradient is dependent on oil density. Subsurface density of oil or condensate depends on composition, amount of dissolved gases, temperature, and pressure. Oil or condensate density can be estimated to useful accuracy if stock tank API gravity and solution gas-oil ratio (GOR) are known.

Estimating oil pressure gradients

Follow the steps listed below to estimate static oil pressure gradient.

1. Estimate oil density using Figure 1.
2. Estimate oil pressure gradient using the following formula:

${\mbox{P}}_{\rm {oil\ grad}}=\rho _{\rm {oil}}\times 0.433{\mbox{ psi/ft}}$

where:

• P_{oil grad} = oil pressure gradient
• ρ_oil = oil density

Determining oil density

Figure 1 Determining oil density.

Use Figure 1 to determine oil density. If the GOR is unknown or if there is no dissolved gas in the oil, use the 0 line.

See also

• Static hydrocarbon pressure gradients
• Estimating static gas pressure gradients
• Plotting the hydrocarbon pressure gradient
• Free water level determination using pressure

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gas-oil ratio