Kick Tolerance - Tutorial
NOTICE: Our Mathcad database got attacked and infected with a virus. Unfortunately, we've had to shut it down until further notice.
You can safely browse the pages, as the Mathcad server was separate to this main website, and was only accessible here. (We used something called an iFrame, which is like a window into a different website).
UPDATE 28th of January 2020: the virus happened just over a week ago. We've temporarily cut and pasted the text parts of the Mathcad pages rather than having blank pages there.
UPDATE 3rd of February 2020: We've been unable to recover the Mathcad worksheets and offer them in a format that provided total security to users. They were published a decade ago, and our IT people say that they would need a complete re-creation with the latest code and security fixes.
APPEAL: These 44 pages were created, and offered as a free resource for over a decade. We know from our website analytics that more than 1000 users visited each month. If only half of these regular visitors donated $20, we would have enough to create an even better solution. As you know, time is money, have these Mathcad pages saved you $20 in time over the years? We expect that they have, not to mention the learning opportunities provided to new engineers entering the industry.
Please, donate at least $20 as a one-off payment, to bring back the drillers Mathcad back as an always free to use resource!
YES! I've gotten value from the drillers Mathcad in the past, and a $20 is a very affordable way of saying thanks. I also want to preserve this tool for future engineers.
NO! I can't or won't donate to the restoration fund. I'm happy to spend a few minutes to offer a testimonial to help encourage the effort. These worksheets do have value. Offer Feedback.
Kick tolerance worksheet, release 9, issued 19 August 2013. JIT version.
(updated and simplified)
Kick tolerance definition; “A description of the volume and pressure of a gas influx that can be safely circulated out of the well“.
This worksheet calculates the volume of an influx taken from drilling into an overpressured formation that can be circulated out of the well without exceeding the assumed or tested strengths of the formations exposed just below the casing shoe. It does not account for gas migration or dispersion in the mud column and it also assumes that no heavy mud exits the bit before the top of the influx reaches the casing shoe. These calculations should not be used for diverter drilling, slimhole drilling (<6″), HPHT conditions or with oil muds where BHP exceeds 6000 psi. The default influx gradient is 1131 Pa/m or 0.05 psi/ft, which is a reasonable gas gradient to use at the pressures encountered at normal well depths.
A swabbed kick may also be calculated for but in this case, please review the JIT version first of all and note the common error that can result in a large overestimate of the kick volume that can be handled. Understanding this, feel free to use the work version afterwards for swabbed kicks.
All inputs can be made in metric or oilfield units. Outputs are given in both unit sets.
User input
1105 |
ftm |
Casing shoe TVD. L_Vshoe =
1.71 |
psi/ftSG or kg/lppglb/ft3ppbkPa/mpsi/m |
Equivalent mud density for the casing shoe strength, estimated or FIT. ρemw =
100 |
psiPakPaMPa |
Optional; safety margin for the casing shoe (reduces the maximum shoe pressure). Pshoe_s =
1.41 |
psi/ftSG or kg/lppglb/ft3ppbkPa/m |
Drilling fluid density anticipated or in use for the section at casing point. ρmud =
0.1198 |
psi/ftSG or kg/lppglb/ft3ppbkPa/mpsi/m |
Estimated influx gradient. ρinf =
1411 |
ftm |
Planned hole section TVD. L_Vtd =
2173 |
ftm |
Planned hole section MD. L_Mtd =
0 |
psi/ftSG or kg/lppglb/ft3ppbkPa/mpsi/m |
Enter the required kick intensity (kick formation pressure gradient – mud gradient). 0 for swabbed influx. ρΔfm_mud =
50 |
FC |
Enter the temperature at the casing shoe. Tfmg =
4.3 |
C per 100 ftC per 100 mF per 100 ftF per 100 m |
Enter the geothermal gradient below the shoe (zero if not accounting for temperature). ZTm =
12.25 |
inmm |
Enter the hole diameter. L_dhole =
5.6 |
inmm |
Enter the drillpipe OD. L_Ddp =
76 |
Enter the inclination at the casing shoe. ΘΔ_Vcs =
Click here when any values are modified to update the result.
Calculations
Calculate the shoe strength
Calculate the current MAASP
Calculate the bottom hole pressure after closing the BOP. This should not be less than mud hydrostatic, if it is a negative kick intensity was used.
Bottom hole pressure
Mud hydrostatic pressure
Methodology
Think of your MAASP as a budget for kick tolerance. You have £500 to spend on food and beer. The more you spend on food, the less you can spend on beer. While you can spend less than you have, you cannot spend more as Nature doesn’t allow you to borrow. Food = kick intensity, beer = loss of hydrostatic due to gas replacing mud. The higher the kick intensity, the less gas you can circulate out of the well without breaking the shoe.
You can also spend a bit on chocolate (choke margin) but this reduces how much you can spend on food and beer combined. Personally I don’t apply a choke margin because there is a hidden safety factor by virtue of the fact that while we assume a single bubble, it is a strung out column of gassified mud which means that the average expansion of the gas is less than if it was a single bubble. The kick tolerance calculations are very sensitive to this, you’re effectively reducing your MAASP by the choke margin applied and the volume you can safely circulate out becomes less.
MAASP =
If a choke margin is applied,subtract this from the MAASP to give the Total Kick Tolerance Budget (combination of kick intensity and gas volume).
From that Total Kick Tolerance Budget, subtract the extra pressure imposed on the casing shoe as a result of the kick intensity to give the Gas Budget. This is the rise in well pressure when the well is closed in and equals kick intensity x true vertical depth. (It will equal Pdp after closing in the well.)
Gas Budget = Total Kick Tolerance Budget – Pdp
The Gas Budget represents the loss in hydrostatic pressure by gas replacing mud. The loss of hydrostatic is the length of the gas column, multiplied by (mud gradient – gas gradient). Therefore the length of the gas column is the Gas Budget divided by (mud gradient – gas gradient). From this we can determine the gas volume at the critical point; with the top of the gas bubble at the casing shoe.
The gas volume must be calculated from the length along hole, accounting for hole inclination.
The volume of gas can now be calculated from the annular capacity between hole and drillstring.
The combined gas law is now used to calculate the volume of influx at the bottom of the well. First, calculate the absolute shoe and bottom hole temperatures and the closed in bottom hole pressure.
Initial shut in influx volume, but test to see if influx height is greater than open hole height, if it is then the influx volume is unlimited.
Results
Kick situation assumed;
Current Maximum Allowable Annular Surface Pressure
Leakoff shoe pressure
Bottom hole pressure after closing in the well
Maximum influx vertical length
Maximum influx volume (gas on bottom) after closing the BOP’s
Recommended Baryte reserve
NOTE – a negative value for the maximum influx volume shows that any kick taken would exceed the maximum shoe pressure.
For the data entered, the
Worksheet references
API RP59. Recommended Practices for Well Control Operations.
Drillers.com Incorporated. Practical Well Planning and Drilling Manual.
Horning, MR. Kick prevention, detection and control; planning and training guidelines for drilling deep, high pressure wells. IADC/SPE 19990.
Sedco Forex Schlumberger. Well Control Manual. Edition of March 1991.
Version 1 of this worksheet was released on 12 February 2008.
Version 6 was released after correcting the conversion factor for kPa/m.
Version 6a was changed for the JIT version, to display intermediate results in both metric and imperial units.
Version 6b was released after revising the variable names in line with the new DDC convention.
Version 6e was released after adding a specific warning if a negative kick intensity is used.
Version 6f was released after adding some more information in the Results.
Version 7 was released after correcting a small error, to account for any safety margin pressure in calculating the influx volume on bottom.
Version 8 was released after realising that there was a much easier way to calculate kick tolerance!
Version 9 corrected an error when calculating for hole inclination at the casing shoe.
