Methods for obtaining formation fluid pressures

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

Methods for obtaining formation fluid pressures can be divided into two groups: measured and estimated. The table below lists the methods by these two categories.

Measured	Estimated
Using RFT (repeat formation tester) data Using reservoir bottom-hole pressure buildup tests Using DST shut-in pressures	Calculating hydrostatic pressures from measured water density or salinity Estimating hydrostatic pressures from fluid density using Rw (formation water resistivity) Using the weight of drilling mud Using the rule-of-thumb pressure gradient, 0.465 psi/ft

Accuracy of measured pressures

RFTs, DSTs, and bottom-hole pressure buildup tests measure formation fluid pressures. Pressure gauge accuracy is a critical factor in all three tests, but the BHP measurement is generally more precise due to the greater time taken for the test. Generally two types of gauges measure pressures: strain and quartz. The table below shows the accuracy and precision of both types.

Gauge type	Accuracy (% Full Scale)	Precision
Strain Gauge	0.18	< 1 psi
Quartz Gauge	0.025	0.01 psi

See also

• Determining formation fluid pressure from DSTs
• Determining formation fluid pressure from RFTs

External links

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drill stem test

bottom hole pressure