Permeability Measurement

Accuracy of Laboratory Permeability Measurements

The accuracy of permeability values measured in the laboratory is generally within approximately ± 5% of its true value when the permeability is in the range of 10 to 500 mD. As permeability decreases to less than one millidarcy, the accuracy may decrease to be within ± 20% of its true value. Above 500 mD, the accuracy of measurements is typically within ± 10% of the true value.

A succession of horizontal permeability values determined by core analysis establishes the vertical distribution of the horizontal permeability at the wellbore. They provide a measure of the permeability variation, which may be used in subsequent reservoir engineering calculations. Buildup pressure tests and analyses from drill stem tests generate very good inter-well permeability values in situ, but give only an average value for the formation permeability and not the distribution of permeability. Both types of data -core and well test – complement each other and have an important role in formation evaluation.

Slippage, relative permeability, reactive fluid and overburden pressure effects can all be measured in the laboratory. They require additional testing time and are usually not measured at the same time that the conventional core analysis is run. The conventional analysis permeability data are only adequate to describe the permeability distribution profiles, to indicate the approximate formation productivity and to serve as a guide for selecting samples to be used in more complex special core analysis tests (SCAL).