PfEFFER Concepts

Movable Hydrocarbon

Movable Hydrocarbon Calculations

Shallow-reading resistivity logs are strongly influenced by fluid saturations in the flushed zone immediately adjacent to the borehole wall. A comparison between hydrocarbon saturations in the flushed zone and the undisturbed formation contrasts "residual hydrocarbon saturation" (flushed-zone hydrocarbons) and "movable hydrocarbons" (the difference in hydrocarbon saturations between the undisturbed formation and the flushed zone).

The computation of fluid saturation in the flushed zone uses the standard Archie equation, but substitutes the resistivity of the mud filtrate, Rmf, and a resistivity reading of the flushed zone, Rxo (typically from a microresistivity device), to compute the filtrate saturation in the flushed zone, Sxo:

The relationship of saturations in the undisturbed formation and the flushed zone is commonly presented graphically as a "movable hydrocarbon plot" to aid interpretations of producibility and the internal structure of a reservoir section.

Figure 21: Schematic movable hydrocarbon plot

This page updated July 2010
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