Methods for obtaining formation fluid pressures

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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