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What do we need to know about kick tolerance but were afraid to ask?
30 December 2020
Following on from post comments on Kick tolerance in 2019.

Having personally had many combative discussions on this in the past. Namely to assure that we fully comprehended, what we stated in our programs was real, evident where all e.g. variability, ranges, risks and uncertainties, presumptions and assumptions made, were all duly sensitised.

What do you/we want to know about kick tolerance but are afraid to ask?
Please raise your questions within this post. 

I have raised this post as my intent is to address all (grey area's) aspects of 'Kick tolerance and MASP' within a Well Control Assurance Program's (W-CAP) specific subject matter session, I am currently working on. Utilising  all independent resources, peer reviews and assists accessible.  

Final product will be an on line 24/7, 365days 'anytime learning' access session for anyone wishing to  to know more about these subject matters, in much more depth and detail required. (Watch this space)

So any key statements you wish to add or gaps to raise regarding current standards, guidelines, knowledge and experience w.r.t KTOL and MASP. 
Please feel free to raise these in your responding post.

e.g. 5 further areas I am seeking to explore, expand and clarify are 
1.  K-tol as a function of time is not often addressed at all. 
e.g. in a shallow hazard, depth, situation where high porosity and permeabilities often exist, flow will be dynamic and rapid. I have experienced 65bbls+ on a connection despite the fact we were using the trip tank as a mitigator to assure early detection.    How are we accounting for this?
2.  MPD in a closed system? where we apparently can measure litres coming into a well.  What are we doing, How do we redefine Ktol in these situations, conditions, environments.
3. When we then take out the MPD and trip the well conventionally . How do we re-dress Ktol now. Or in risk and safety terms, is it considered better to remain in MPD mode throughout? 
5. In HPHT wells transitions zones (with low permeabilities) where we are often underbalanced without knowing this, how do we address sensitivity of Ktol now.
5.  On balance underbalanced drilling, where the well is and can flow. What are the kick tolerance limits, guidelines now. 
6. What else SPREAD members?

So anything to add or gaps you see that exist. All comments, discussions, welcomed.

Finally here's wishing all SPREAD members a happy and a far better new year in 2021.



5 answer(s)
Wells Mgr - Wellspec
Total Posts: 48
Join Date: 23/03/16

Be more than happy to help out, Have done a lot of work on KTol with respect to MPD.
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 502
Join Date: 10/01/05
Had a enterprise copy of Steve D's mathcad Ktol worksheet that used to be @

Spent about an hr today converting this to  a working mathcad prime 6.0 version. 

Once i have had this checked at source (with Steve D).

Any other mathcad users out there, want a copy, let me know.


Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 502
Join Date: 10/01/05

Great comments afforded, thanks for taking the time to respond.

Where via other external responses received. And the fact that I have since invested to download several Ktol 'OnePetro papers', to review. Where it was noticeable that quite a few in the last few years, are trying to better address 'Ktol for the more complex wells'.

I am also now in communication and collaborating with three SME's on this subject i.e. A former Drilling manager of mine, whom I worked with on several top quartile wells, my Well control expert buddy, and someone who has made Ktol his passion. 

So I am building a diverse and variant team that i may need to add a pore pressure and geo person to assure we look at this from all directions.    

Intent is as always would be to build an (physical (parts) people paperwork) evidence based approach to Ktol and surrounding. issues, gather all to try and make more sense of all, then act (who when what why how) to translate and deliver some sustainable learning. Maybe a really useful whitepaper as well?

Where from my part I simple hope to develop a skills development session blended e-learning session for well management and operations persons at the end of this process.

That I/we will probably test run first via the go-to-training platform that I am paying for and subscribing too.

Ill keep everyone informed when this test session is ready to be trialled.

If interested to attend and participate, let me know.

Thanks again.   


Drilling Mgr
Cairn Energy
Total Posts: 19
Join Date: 15/01/09
Kick tolerance is my pet hate and I wish the drilling industry would come up with something better to replace it. It's fine as a qualitative indicator in well design as to whether the correct casing setting depths have been chosen to get adequate shoe strengths for well control purposes but it's usually only qualitative because of the assumptions used.

In operations it is of little use due to the numerous variables, particularly in exploration wells. The biggest one is that the kick tolerance depends upon the kick intensity which is generally assumed from a pore pressure prediction rather than known. 

The LOT at the shoe is often not easy to pinpoint from the LOT chart, the wellbore often strengthens with time, and as drilling has continued a weaker formation may have been exposed. So we don't really know the breakdown pressure in the open hole very well.

Then there's the issue of how the calculation is done. I often see simple spreadsheets being used which don't take into account of gas compressibility, temperature or flowrate at the time the kick is taken. They often assume a single bubble of a simple gas and take no account of gas going into solution.

So, many unknowns. I remember a driller on a rig saying that there was no rush to close the well in since he had an eighty barrel kick tolerance. Ever since then I've been opposed to telling drillers what the kick tolerance is - they simply need to shut in an influx as quickly as they can to minimise that influx. Once we have some real data we can start to work out what the kick tolerance really is. And by then the gas has likely migrated past the shoe anyway.

It would be great if this thread can lead to improvements in how we deal with kick tolerance as an industry.
Wells Mgr - Wellspec
Total Posts: 48
Join Date: 23/03/16

Kick tolerance is defined to ensure that we can safely circulate out an influx without breaking down the formations. But it is a completely static scenario, well is closed and the flowing formation is contained by the pressures in the wellbore.

Kick tolerance has two parameters, influx intensity and influx volume. It does not change if we are using managed pressure drilling or underbalanced drilling. The wellbore has two parameters that set the limits, one the fracture pressure at the weak point, the other one is the pore pressure of the flowing formation.

Circulation rate or inflow rate are not part of the kick tolerance calculations. Some people do not even consider intensity in the kick tolerance, swab kicks only. The inflow rate is basically providing a volume.

In an open wellbore we have a wellbore pressure controlled with the mud density. The influx intensity is purely based on the pore pressure in the flowing formation. If the wellbore pressure is 12 ppg and the flowing formation is 14 ppg the intensity is 2 ppg. The volume is based on how fast the influx is detected and the wellbore is closed to contain further inflow. Intensity = SIDP volume = SICP. The faster the influx is detected and the well bore is closed the smaller the volume.

With a closed wellbore in managed pressure drilling we have a wellbore pressure that is a combination of mud density and applied surface pressure. The intensity of an influx remains the same (same pore pressure). We can have a mud weight of 11 ppg and a 1 ppg equivalent surface back pressure but drilling into the same 14 ppg pore pressure flowing formation still provides an intensity of 2 ppg.

The big advantage with MPD is the rapid detection provides a smaller influx volume. The well is already closed and adding surface pressure stops the inflow.

If we then close the BOP to circulate out the influx we are back to the same scenario as with conventional drilling.

An influx from a formation with a pore pressure higher than the weak point pressure still results in an underground blowout. Kick tolerance does not change for MPD or conventional drilling the pressure limits in the well are still defined by the weak point and the pore pressure.

In underbalanced drilling we know the pressure from the flowing formation. The well is full of reservoir fluid and the surface pressure is controlled to minimize the flow of hydrocarbons. If the well is closed in and the weak point fracture pressure is lower than the formation pressure of the reservoir formation we still end up with an underground blowout.

If you really want to make this complex look at kick tolerance in aerated drilling operations where we pump nitrogen in the drilling fluid and then take an influx.

The challenge with the kick tolerance is that there is no standard way to calculate it. Different approaches are taken, some consider the intensity other companies look at swab kicks only.

The inflow rate from the reservoir and the pump rate disperses the influx in the drilling fluid which is not factored in the calculations.

Kick tolerance calculations are based on a defined block of gas in the well bore with a density of methane. That volume is taken to the weak point depth where pressures are re-calculated based on simple gas laws. If the gas is dispersed or even in solution in an oil based mud system the density of the block of gas is no longer gas, but it is drilling fluid.

A great subject for a well control class discussion and in MPD operations a topic that is raised at almost every project.

Looking forward to some more answers.

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