1. Formation Evaluation procedure:-
To generate a formation evaluation model by Techlog software, the following steps
must be done.
The first step to be done by the user is to upload the LAS file from the computer
hardware to Techlog software by the order "import". As this LAS file contains
acquisition data which is acknowledge from the wire line data record.
Secondly the user must do quality control process on the LAS file data to assure that
each data file such as GR, Neu-porosity, resistivity data, PEF, BS, caliper data and the
bulk density has its own family name and the righteous aliases name too.
Thirdly the user must put three log tracks next to each other to run the mentioned logs
on those log tracks. The first log track from the left the user may run GR log BS log
and caliper log on it, the second (middle) log track the user may run the resistivity logs
on it, the third and the final log track the user may run the Neu-porosity, bulk density
and the PEF log on it to acknowledge the properties of each depth interval on the log
depth and to evaluate the formation depth intervals easily.
Fourthly the user must make sure either that well is vertical well or deviated as if it’s
deviated a true vertical depth must be assigned to the log view data besides the other
log tracks to define the depth interval zonation (aquifer depth intervals, HC depth
intervals and lithology depth intervals) correctly.
Now the user is ready to begin the calculations needed for essential formation
evaluation, as the fifth step objective is considered to be the very first point of the
calculation procedure line as the user first calculation task is to calculate the shale
volume which is also referred to by VSH
VSH calculation method very simple as it can be done by the following procedure:
From the upper horizontal order bar the partition “Log” is choosed then choose the “V-
shale” calculation by GR order to begin the shale content volume calculation, then
choose the GR and input it in the gamma ray slot and create the VSH log and save it
into the variables tab. This output will help us to define the highest shale content zone
and zonate it as Shale content zone.
2. After all data needed for the zonation step is now available, the sixth step may be
constructed now as it’s the zonation step.
Zonation concept is considered to be or defined to be a step in the general formation
evaluation procedure as it’s very important for many ongoing steps to be done after the
zonation step.
Zonation can be done by monitoring the logging data of depth intervals over the well
true vertical depth, and evaluate the depth interval as the logging data shows.
Aquifer , HC-bearing formation and shale content zone can be identified as follows:
The aquifer zone is considered to be the depth interval where the formation bears
formation water, and on the log tracks the aquifer zone can be illustrated by depth
interval logging readings as the low reading of GR log represents the possibility of
lithological reservoir presence ( Sand or carbonate formation), also as the water of the
formation is considered to be conductive for the electricity so when the resistivity
measuring tool send current to the formation it breaks through it so the resistivity in this
depth interval would be very low due to the presence of formation water.
HC-bearing formation is acknowledged by also the low reading of the GR log and as
the HC fluid is considered to be an insulator fluid then the resistivity reading of it must
be reasonably high if it’s oil content or very high if it’s gas content, also a crossover
between the Neutron porosity reading and the bulk density reading will be essential as
it differs between the dry formation and the wet formation, as if it was water wetting or
oil wetting (liquid saturation) the crossover would be relatively small and if the
formation bears gas the crossover will be relatively big due to gas effect phenomena.
The last zonation illustration is the lithology identification and it can be known by the
GR log and the PEF log as if the gamma ray crosses the baseline then it can be either
shale content or radioactive sandstone and then we use the PEF log to differ between
then as the shale/Dolomite PE reading is 2.5-5 and the sandstone PE reading is below
2. So by this GR and PEF log tacks data information we can easily define the lithology
of each depth interval.
By all the above information about the Techlog zonation technique we can conclude
the needed information between the logs to identify the HC pay zone, as if the data
3. required for that are consistent in all the logs at the same depth intervals then it seems
to be very helpful to evaluate the aquifer zone, HC pay zone and the shale zones.
The seventh step after the zonation step is to run a cross plot between the neutron
porosity and the bulk density logging data to compare the lithology zonation done in
the previous step to the cross plot lithology chart and see if the lithology identification
is correct or need to be revised.
The eighth step in formation evaluation is considered to be porosity calculation as al
the needed data to evaluate the total porosity and effective porosity are now available
as the neutron porosity , bulk density and deep resistivity are acknowledged, so now
the we can calculate the total porosity logs using the Neutron-density method.
Also the effective porosity can be used by the acquired data from the LAS file logs such
as the neutron porosity, bulk density and the deep resistivity to acknowledge the
effective porosity log, but there is a little difference between the total porosity
calculations and effective porosity calculations which is the VSH log as it’s known that
the shale barriers have very high porosity but it has very low permeability which can
reach to zero value, so it’s considered to be useless in the calculations of effective
porosity so the VSH must be added to the needed parameters for effective porosity
calculations to be subtracted from the effective porosity values along the well depth.
The ninth step of this project formation evaluation is to determine the cementation
factor and water resistivity of the formation and this can be demonstrated by using
picket plot which is considered to be a very helpful way to define the cementation factor
(m) and the water resistivity (Rw) (and this method can be used when the core analysis
of the formation is not available).
The tenth step is to calculate the total water saturation (Dual water method) by using
the Quanti calculation partitions after we demonstrated all the data needed to calculate
this such as the deep resistivity which was available from first place, the VSH which
was calculated from the fifth step and finally the total porosity acknowledged from the
eighth step, now we can calculate the total porosity logs.
Also with the same data needed for the calculations of the total saturation, we can use
the same data to calculate the effective saturation (using Indonesia method) but with
slight distinction as we want to calculate the effective saturation so we will replace the
4. total porosity with the effective porosity data demonstrated by the effective porosity
calculation, so now all we need is deep resistivity, VSH and the effective Neu-Den
effective Porosity.
Now the eleventh step which is considered to be the final step is to do a summary for
the most important acknowledged data from the past procedure which may help in
calculating the reserve estimation for each well.
So from “Quanti” data calculation partition we can choose “summarize” choice to sum
up the most important data calculated through the formation evaluation procedure
which (especially in the zonation log tracks that we did in the sixth step) and the
importance of the data is determined by if it’s needed to calculate the reserve of the
field, so the needed data for this process is the effective porosity, effective saturation ,
total porosity ( quality control method as to monitor that the average summarized total
porosity is larger than the average summarized effective porosity) , VSH and the
Techlog software calculate the net pay thickness in this step automatically.
