The Digitally Focused Laterolog (DFL) provides measurement of near borehole formation resistivity. The DFL is an integral and inseparable component of the HRID.
The primary objective of logging DFL is to estimate the depth of fluid invasion and determine the flushed-zone resistivity (Rxo). Correction must be applied for borehole and invaded fluids to obtain more accurate value of Rxo.
With knowledge of Rxo and porosity, water saturation in the flushed-zone can be calculated using Archie’s equation.
If Sxo=Sw before invasion, then after invasion if there exists moveable hydrocarbon, then the hydrocarbon will be flushed away by the mud filtrate, hence Sxo will be greater than Sw. This is an indicator for the zone contains some moveable hydrocarbon.
When DFL combined with other resistivity curve, this will give us qualitative value for permeability of the formation. If there exists permeability, this should be seen on the log as separation between DFL, Shallow and Deep Resistivity. Again, the more contrast Rmf to Rw, the more separation can be seen on the log.
Logging Environment :
This tools is a laterolog tool, means that the tool injects current to formation. This requires existence of conductive fluid. Hence, DFL works best in conductive muds, also capable for fresh-water based muds. But cannot be used for oil-based mud or air.
The depth of investigation for DFL is 17 inches, with less than 17 inches for vertical resolution.