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Buoyancy pressures caused by hydrocarbon columns can be recognized by comparing hydrostatic pressure gradients with formation pressures. Pressures exceeding expected hydrostatic pressures could be due to the presence of hydrocarbon columns.

[[Buoyancy pressure]]s caused by [[hydrocarbon column]]s can be recognized by comparing [[Normal hydrostatic pressure gradients|hydrostatic pressure gradients]] with formation pressures. Pressures exceeding expected hydrostatic pressures could be due to the presence of hydrocarbon columns.

Two items are critical for detecting buoyancy pressure in a well:

Two items are critical for detecting buoyancy pressure in a well:

* Accurate static water plot for the well

* Accurate static water plot for the well (See [[Constructing a hydrostatic pressure-depth plot]])

* Reliable formation fluid pressure measurements

* Reliable formation fluid pressure measurements (See [[Methods for obtaining formation fluid pressures]])

 

This section discusses how to detect the presence of hydrocarbons using formation fluid pressures.

==Procedure==

==Procedure==

The table below outlines a procedure for using pressures to detect the presence of a hydrocarbon column in a formation.

The list below outlines a procedure for using pressures to detect the presence of a hydrocarbon column in a formation.

# Make a [[Plotting the hydrocarbon pressure gradient|hydrostatic pressure-depth plot]] through the interval of interest.

# Plot the pressure(s) measured from the interval of interest.

# If the measured formation pressures are greater than the hydrostatic pressure, then the formation may contain a hydrocarbon column.

# Check to see if anomalous pressures make geological sense.  

#* ''' Example: ''' Measured fluid pressure is [[pressure::250 psi]] over the static water pressure. The formation is believed to contain 30°API [[oil gravity|gravity oil]], and the total vertical trap closure is [[length::500 ft]].

#* ''' Solution: ''' If the 250-psi pressure is due to the presence of a hydrocarbon column, then a column of [[depth::2500 ft]] of 30°API [[gravity]] oil would have to be present in the trap (assuming a [[Constructing a hydrostatic pressure-depth plot#Rules of thumb|freshwater gradient]]). Vertical trap [[closure]] is only [[length::500 ft]]; therefore, the measured formation pressure does not match the geology and is probably wrong.

| Make a hydrostatic pressure-depth plot through the interval of interest.

| Plot the pressure(s) measured from the interval of interest.

| If the measured formation pressures are greater than the hydrostatic pressure, then the formation may contain a hydrocarbon column.

| Check to see if anomalous pressures make geological sense. <break> </break> ''' Example: ''' Measured fluid pressure is 250 psi over the static water pressure. The formation is believed to contain 30°API gravity oil, and the total vertical trap closure is [[length::500 ft]]. <break> </break> ''' Solution: ''' If the 250-psi pressure is due to the presence of a hydrocarbon column, then a column of [[depth::2500 ft]] of 30°API gravity oil would have to be present in the trap (assuming a freshwater gradient). Vertical trap closure is only [[length::500 ft]]; therefore, the measured formation pressure does not match the geology and is probably wrong.

==See also==

==See also==

* [[Static hydrocarbon pressure gradients]]

* [[Static hydrocarbon pressure gradients]]

* [[Methods for obtaining formation fluid pressures]]

* [[Methods for obtaining formation fluid pressures]]

==External links==

==External links==

[[Category:Critical elements of the petroleum system]]  

[[Category:Critical elements of the petroleum system]]  

[[Category:Formation fluid pressure and its application]]

[[Category:Formation fluid pressure and its application]]