What are the differences between Formation Integrity Test (FIT) and Leak Off Test (LOT).?

You may confuse between Formation Integrity Test (FIT) and Leak Off Test (LOT).

They are different in this following aspect.

Leak Off Test – you pressure test shoe and formation until formation break down.

Let’s I explain more about it: Leak off Test is conducted in order to find the fracture pressure (fracture gradient) of formation and shoe. When conducting the LOT, you will pump drilling fluid to until you see the fracture trend of formation. Once formation is fractured, the first pressure that deviated from a trend is typically called Leak Off Pressure. We use the leak off pressure to calculate LOT.

Formation Integrity Test – you test strength of shoe and formation to designed pressure.

Let’s I explain more about it: Formation Integrity Test is typically used for testing strength of formation and shoe by increasing Bottom Hole Pressure (BHP) to designed pressure. When you do the FIT test, you will increase surface pressure until it reaches the required pressure only. There is no intention to break the formation with FIT. You will do FIT to ensure that you will be able to drill to section target depth and will be able to control the well in case of well control situation without underground blow out.

In term of a calculation, both FIT and LOT have the same formulas. You can read more detailed calculations about Formation Integrity Test (FIT) and Leak Off Test (LOT).

Ref book: Drilling Formula Book Formulas and Calculations for Drilling, Production and Workover, Second Edition

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14 Responses to What are the differences between Formation Integrity Test (FIT) and Leak Off Test (LOT).?

  1. kolawole adetokunbo says:

    nice explanation about FIT & LOT

  2. kolawole adetokunbo says:


  3. Almaz says:

    Just to clarify – so, LOT and FIT are done after drilling rat hole out of casing shoe? And LOT pressure is greater than FIT pressure?

  4. Oluseye Ogunyemi says:

    I think we can also define FIT pressure as that point equivalent to the fracturation pressure at which the hydrostatic pressure is sustained by the formation pressure in the rat hole for a defined time while the LOT pressure is that beyond the the fracturation pressure at which the hydrostatic pressure is not sustained by the formation pressure.

  5. engineer says:

    whats mean lot

  6. nizam says:

    Nice explanation, thank you for it.

    For LOT, we cement again to close the fracture in order to proceed further drilling, yes?


    • Nizam,

      Typically, the cement will not be performed in order to close the fracture. You will start drilling after LOT.
      In some special cases, you may need to do cement squeeze to strengthen the shoe if you don’t get minimum LOT.


  7. Ahmed says:

    Actually, we did two times FIT test, but the test is negative, now we performed squeeze.

  8. ern says:

    dude, really?

    i live for and love short and sweet explanations!!! thanks…

  9. Nilesh says:

    When exctlu we do FIT and LOT ??

  10. Nilesh says:

    When exactly we do FIT and LOT??

    • FIT is used when you want to reach only the designed shoe pressure. This will confirm the well design criteria.
      LOT is tested until the formation is fracture. You will know formation strength and it will tell you if your designed limit is acceptable for drilling next section.


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