Difference Between Leak off test, Formation integrity test & Formation breakdown test

While Leak off test, Formation integrity test & Formation breakdown test all have the same procedure and aim, the only difference is the point to which the casing shoe will be pressured.

Leak off test

Formation integrity test (FIT) is conducted when we already know how much maximum pressure next open hole section could experience.for e.g if Maximum pressure open hole section could experience is 2600 psi we will just pressure the casing shoe slightly higher than 2600 psi pressure for safety margin. If at this pressure formation is intact we will have have a straight line plot between Surface pressure and Cumulative volume i.e in the above plot it will lie between point ‘o’ and ‘a’ and the test will be called Formation integrity test.

if the test is conducted to the point when the drilling fluid starts to leak into the formation i.e between point ‘a’ and ‘b’ it is Leak-off test (LOT).Between point ‘a’ and ‘b’ only micro-fractures have developed into the formation which are very small in size and are recoverable, if the pressure is reduced will again close.

‘b’ is the point at which actual fracturing takes place and these fractures are permanent in nature.If the test is conducted beyond ‘b’ it will be termed as Formation breakdown test (FBT). Remember it is not recommended to go beyond point ‘b’ as by doing so we will be inducing permanent fractures into the formation which can cause lost circulation while drilling ahead.

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