Formation integrity test (FIT)

An accurate evaluation of a casing cement job as well as of the formation is extremely important during the drilling of a well and for subsequent work. The Information resulting from Formation Integrity Tests (FIT) is used throughout the life of the well and also for nearby wells. Casing depths, well control options, formation fracture pressures and limiting fluid weights may be based on this information. To determine the strength and integrity of a formation, a Leak Off Test (LOT) or a Formation Integrity Test (FIT) may be performed. This test is first: a method of checking thecement seal between casing and the formation, and second: determining the pressure and/or fluid weight the test zone below the casing can sustain. Whichever test is performed, some general points should be observed. The fluid in the well should be circulated clean to ensure it isof a known and consistent density. If mud is used for the test, it should be properly conditioned and gel strengths minimized. The pump used should be a high-pressure, low- volume test or cementing pump. Rig pumps can be used ifthe rig has electric drives on the mud pumps, and they can be slowly rolled over. If the rig pump must be used and the pump cannot be easily controlled at low rates,then the leak-off technique must be modified. It is a good idea to make a graph of the pressure versus time or volume for all leak-off tests.

The main reasons for performing formation integrity test (FIT) are:

- To investigate the strength of the cement bond around the casing shoe and to ensure that no communication is established with higher formations.

- To determine the fracture gradient around the casing shoe and therefore establish the upper limit of the primary well control for the open hole section below the current casing.

- To investigate well bore capability to withstand pressure below the casing shoe in order to validate or invalidate the well engineering plan regarding the casing shoe setting depth.