1. Resistivity Logs High deep resistivity means:
Hydrocarbons
Tight streaks (low porosity)
Low deep resistivity means:
Shale
Wet sand
Separation between resistivities means:
The formation fluid is different from the drilling fluid
The formation is permeable to the drilling fluid
Deep, Medium, and Shallow refers to how far into the formation the resistivity is reading (4 ft, 2 ft, few in)
ILD (deep)
MSFL
SFL
Formation Fluid
different from
Drilling Fluid
SLIDE 9
Another common log measures the electrical resistivity of the formation
Tools are designed to investigate different distances into the rocks
Shallow = a few inches into the formation
Medium = about 2 feet into the formation
Deep = about 4 feet into the formation
If the deep resistivity is high = either HCs or low porosity tight streaks
If the deep resistivity is low = shale or wet sand
If there is separation between the medium and deep measurements, it means
The formation fluid is different from the drilling fluid, and
The formation is permeable to the drilling fluid
On the log that is shown,
deep = black; red = medium
The region boxed in red – the curves are separated, hence formation fluid different from drilling fluid
E.g., if drilling fluid = water, then interval does not have water in the pore space
The region boxed in green – the curves are NOT separated, hence formation fluid same as drilling fluid
Formation Fluid
similar to
Drilling Fluid
Courtesy of ExxonMobil
L 4 - Well Log Data