Electrofacies and Cut Off determination to Evaluation Vulcaniclastic Reservoir at Air Benakat Formation, South Sumatra Basin


The subsurface data in the form of well logs
for the interval Air Benakat Formation in the
study area is composed by lithological
variation in the form of sandstone and
silisiclasticsandstone vulcaniclastic with
repeated its presence, has a fairly complex
character log. The presence of volcanic
rocks clastic depositional events recurring
effect on electrical tape log is not good,
causing difficulties in the correlation,
internal zoning and determination of
reservoir properties.
Determination of cut-off is needed to
identify the zones of permeable and nonpermeable formations are affected in a
range of vulcanic material. The right cut off
very helpful to get distribution electrofacies.
According to Li Guoxin et al, 2008,
vulcaniclastic reservoir matrix has the same
character with the silisiclasticreservoir in
general, but the geometry of the
relationship between porosity and pore
similar to the character of porosity in
carbonate rocks. Based on the statement of
the approach to determine the cutoff in
vulcaniclastic reservoir petrophysical study
can not be equated with the determination
of cut-off for silisiclastic reservoir. However,
special workflow required to obtain the
distribution and geometry ofreservoir.
The methodology used by multiple
approaches crossplot. Crossplotof resisitivity
log distinguished sandstone and shale.
Thendistinguish between vulcanic and nonvulcanic sandstone is the PEF vsdeep
resisitivity crossplot, verified with the results
of petrographic analysis. Micro-resistivity
crossplot then performed with deep
resistivity to distinguish permeable zone and
non-permeable zones in the zone ranges
indicated as vulcanic clastic reservoir.