There is a fundamental error in these freely available “Toolkit” kick tolerance calculators which make them extremely dangerous software which is why they should not be used to calculate kick tolerance volumes.
The problem with these freely available “Toolkit” kick tolerance calculators are that they allow formation / pore pressure gradients less than mud weight to be input for “swabbed” kicks which results in invalid kick tolerance volume to be calculated.
If a swabbed kick is taken then the bottom hole pressure is equal to the mud weight when the kick is circulated out. Technically when killing all wells, the bottom hole pressure is either equal to the mud weight for “swabbed” kicks or greater than the mud weight for “drilled” kicks. The bottom hole pressure is never less than mud weight.
These freely available “Toolkit” kick tolerance calculators allow the user to input bottom hole pressures less than mud weight which is completely wrong.
If you want to determine if you have a dangerous KT calculator then run the swabbed kick tolerance calculations with a formation / pore pressure gradient equal to mud weight (KT vol 1) then repeat KT calculations with a formation / pore pressure gradient less than mud weight (KT Vol 2). If KT Vol 1 is not equal to KT vol 2 then you have extremely dangerous KT software as it generates invalid kick tolerance volumes.
I have run an example Kick Tolerance calculation on one of these “Toolkit” programs and compared it to the results from my Ultimate Kick Tolerance Calculator to demonstrate why these programs are so dangerous and why they should not be used.
An example from one freely available “Toolkit” kick tolerance calculator
The kick tolerance calculations are shown below for the “Toolkit” program. The fracture gradient at the shoe is 13.9 ppg, the planned mud weight is 13.5 ppg which gives a 260 psi overbalance over the maximum formation pressure of 13.0 ppg. The kick tolerance calculator calculates that you have a “swabbed” kick tolerance of 25.8 bbls with 13.0 ppg formation pressure increasing to 412.7 bbls with 9.0 ppg formation pressure. There are no error messages.
To most users this hole section would meet the well integrity policy requirement of greater than 25 bbls as the calculated minimum kick tolerance volume is 25.8 bbls going up to a maximum of 412.7 bbls.
If you don’t understand kick tolerance then you think that you have a well design that exceeds the well integrity policy of greater than 25 bbls.
If you know anything about kick tolerance then you know that it is impossible to have a kick tolerance volume for 25.8 to 412.7 bbls when the circulating MAASP is only 4 psi.
The true Limited Kick Tolerance volume for this scenario is only 0.3 bbls as correctly calculated by the Ultimate Kick Tolerance Calculator (see UKTC output below)
These freely available “Toolkit” kick tolerance calculator programs are basically random number generator as the calculated kick tolerance volumes can be out by 1,375 times the correct number (Correct value 0.3 bbls versus incorrect value 412.7 bbls)
All of the kick tolerance volumes calculated by the “Toolkit” kick tolerance calculator below are completely invalid and erroneous numbers but to the inexperienced user they look 100% correct.
“Toolkit” kick tolerance calculator swabbed kick output
The Ultimate Kick Tolerance Calculator output below shows that for a maximum allowable pressure increase at casing shoe of 4 psi (Toolkit equivalent “circulating MAASP = 4 psi”) the real calculated kick tolerance volume is only 0.3 bbls swabbed kick. The toolkit calculated swabbed kick tolerance volumes are 86 times (25.8 bbls) to 1,375 times (412.7 bbls) greater than the actual correct kick tolerance volume of 0.3 bbls.
UKTC swabbed kick output for the same scenario as used in the “Toolkit” KT calculator
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