A Formation Integrity Test (FIT) is a test performed to check the strength of the formation and shoe by increasing the bottom hole pressure (BHP) to the surface pressure. For successful drilling and completion of a well, an accurate evaluation of a casing cement job and the formation is very critical.
FIT is conducted to ascertain the resistance offered by the drilled formation and to ensure that the formation below the casing shoe will not fracture when the new formation is being drilled.
Performing a FIT requires using the rig's mud pumps, closing the blowout preventer (BOP) and incurring non-productive time (NPT). Information obtained from a FIT can be used to base factors such as casing depths, well control options, formation fracture pressures, and limiting fluid weight.
The formation integrity test (FIT) is conducted to:
1. Investigate the bonding strength of the cement around the casing shoe to ensure that there is no communication with higher formations.
2. Establish the upper limit of the mud weight which is the primary well control barrier by estimating the fracture gradient around the casing shoe.
3. Reduce the risk of inducing a fracture during cementing operations.
4. Determine optimum and equivalent mud weights for drilling the next section.
5. Select casing seats and planning for hydraulic fracturing.
6. Collect information for optimizing well designs for future projects.
FIT is included in the drilling program to minimize uncertainties related to the formation. Regularly conducting FITs can be beneficial for the wellbore as the data helps in maintaining wellbore stability, pore pressure, and optimizes drilling, casing and cementing operations.