Formation Integrity Test (FIT) Procedure and Calculation

Formation Integrity Test is a method to test strength of formation and shoe by increasing Bottom Hole Pressure (BHP) to designed pressure. FIT is normally conducted to ensure that formation below a casing shoe will not be broken while drilling the next section with higher BHP or circulating gas influx in a well control situation. Normally, drilling engineers will design how much formation integrity test pressure required for each hole section.

The formula below demonstrates you how to calculate required FIT pressure.

Oilfield Unit

Pressure required for FIT = (Required FIT – Current Mud Weight) × 0.052 × True Vertical Depth of shoe


Pressure required for FIT in psi

Required FIT in ppg

Current Mud Weight in ppg

True Vertical Depth of shoe in ft

Note: FIT pressure must be rounded down.

Required FIT (ppg) = 14.5
Current mud weight (ppg) = 9.2
Shoe depth TVD (ft) = 4000 TVD
Pressure required for FIT = (14.5-9.2) × 0.052 × 4000 = 1,102 psi

Metric Unit

Pressure required for FIT = (Required FIT – Current Mud Weight) × 0.00981 × True Vertical Depth of shoe


Pressure required for FIT in KPa

Required FIT in Kg/m3

Current Mud Weight in Kg/m3

True Vertical Depth of shoe in m

Note: FIT pressure must be rounded down.

Required FIT (Kg/m3) = 1740
Current mud weight (Kg/m3) = 1100
Shoe depth TVD (m) = 1300 m
Pressure required for FIT = (1740-1300) × 0.00981 × 1300 = 8,161 KPa

Formation Integrity Test (FIT) guideline is listed below: (note: this is just only guide line. You may need to follow your standard procedure in order to perform formation integrity test):

1. Drill out new formation few feet, circulate bottom up and collect sample to confirm that new formation is drilled to and then pull string into the casing.

2. Close annular preventer or pipe rams, line up a pump, normally a cement pump, and circulate through an open choke line to ensure that surface line is fully filled with drilling fluid.

3.Stop the pump and close a choke valve.

4. Gradually pump small amount of drilling fluid into well with constant pump stroke. Record total pump strokes, drill pipe pressure and casing pressure. Pump until casing pressure reaches the pressure required for formatin integrity test. Hold pressure for few minutes to confirm pressure.

5. Bleed off pressure and open up the well. Then proceed drilling operation.

Please find the Excel sheet – calculate pressure required for formation integrity test.


Ref books: 

Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.

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27 Responses to Formation Integrity Test (FIT) Procedure and Calculation

  1. Hamoud says:

    Hello dearsir I am a driller and I am looking for more and more information about the drilling and formula from your site

    so please send to me as much as you can

    Thank you

  2. Raymond Uzor Anuforoh says:

    i truely appreciate the article. i would like to receive more of this information.

  3. Luis Pereira says:

    Hi there,
    Thanks for this. Maybe it is a dumb question, I am Just wondering how we determine the required FIT (ppg some operators prefer sg). And another question, just some thing that come in my mind in regard with determining the exact depth of lost circulation just happened, how we know for sure about which depth that cause a lost circulation.

    Many thanks,

    • You can get it when you determine Kick Tolerance Calculation. You will have a idea what is the minimum strength at shoe.

      For the exact depth of lost circulation, I don’t have the way to determine the exact the depth of lost circulation. You may try to figure out based on the LWD but it is not the precise way to get it.

  4. mohammed attia says:

    thank you verey verey verey much for all the information which are supply to us
    you are solve many problems to me

    thanks a lot and good luck

  5. wangfs says:

    what is formation interval test ? what’s difference between the formation interval test and formation integration test ?
    thanks a lot

  6. wangfs says:

    can you offer more detailed information on FIT ? purpose , procedure , concept ,

  7. Clay says:

    Can you tell me the equation to figure up BBLs to achieve your FIT test pressure? Thanks

    • There is no equation showing the BBL and FIT. You will see that many charts are plotted between BBL and pressure in the FIT chart. These will tell you the behavior of the formation with volume pumped while performing FIT.

      • Tawn says:

        This equation is pretty accurate – give it a try..
        Total volume of test fluid X Test Pressure Divided by 275,000 = bbls to reach test pressure. You can take it a step further and turn that into strokes to reach test pressure.

        ex: Hole volume = 200bbl
        Test Pressure = 3000psi

        200 x 3000 = 600,000
        600,000/275,000 = 2.18bbls To achieve test pressure of 3000psi
        2.18bbl / pump output (say .070) = 31.16 strokes to reach 3000psi

        Good luck

  8. chris says:

    What about performing an FIT on air? Would your current MW just = 0, so in your above example the required test pressure would be 2912 psi?

  9. Jason says:

    If your drilling on air dipshit you wouldn’t need to do fit test because your not concerned about going on losses assbag

  10. waqar ahmed says:

    please tell me .how we select or picking casing point on the base on pressure??????

  11. Nilesh Desale says:

    It is very helpful thank you. Can you send a soft copy regarding all drilling formulas. So that if I can keep in my mobile or in my laptop and carry everywhere. Or else if you have already made any application for android phones for all the formula’s so please let us know that where I can find it.
    Thank you.

  12. v.bihariesingh says:

    What is the difference between FIT and formation mechanical integrity.

  13. Abdo says:

    Thank you guys. you are going a good work.

  14. Mehdi says:

    Thanks for your effort.
    I saw that some guys interest to do FIT from annalus.
    could you please tell me what’s advantage and disadvantage in both method(from string and annulus)
    and also what’s reason that somebody use sea water for testing?

  15. G.Koniber says:

    Thanks so much for this and for all


    I think such tests are being done to either confirm data or get data

    Such as the proper MW, and so on

    In such away I wondered if I knew the required FIT MW why this FIT will be done?!!

    • FIT is based on Kick Tolerance design. Kick tolerance is the maximum gas volume for a given degree of underbalance which the circulation can be performed without exceeding the weakest formation in the wellbore.

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