Integrity Testing Training (FIT) is the method of testing the strength of the formation and a casing shoe by increasing the bottomhole pressure (BHP) to the design pressure. FIT is normally carried out to ensure that the formation below the casing does not rupture while the next section is drilled with higher bottomhole pressure. Normally, drilling engineers in town will design how much formation integrity test pressure is required and a unit of FIT is normally in pounds per unit gallon.
How to calculate the pressure required for the formation integrity test.
Before performing the formation integrity test, you must know the pressure required for the formation integrity test. The formula below shows you how to calculate the required FIT pressure.
Required FIT Pressure (psi) = (Required FIT in ppg – Actual Mud Weight in ppg) x 0.052 x Actual Vertical Depth of Footing in ft
The following example demonstrates how to use the formula to calculate the pressure required for the test:
FIT required (ppg) = 14.5
Current mud weight (ppg) = 9.2
Actual Vertical Depth of Footing (ft) = 4000 TVD
Required pressure for FIT = (14.5-9.2) x 0.052 x 4000 = 1102 psi
Note: Acronyms are listed below;
psi = pounds per square inch
ppg = pounds per gallon
feet = feet
The Integrity Test Training (FIT) procedures are as follows;
1. Drill a new formation a few feet, circle from the bottom up and collect formation samples to confirm the new formation is drilled, then pull a drill string to the casing shoe.
2. Close annular preventer or pipe rams, align a cement pump, and run through an open choke line to ensure the surface line is completely filled with drilling fluid.
3. Stop the pump and close a throttling valve.
4. Gradually pump a small amount of drilling fluid into a well with constant pump strokes, and the recommended pump strokes are 5 to 10 strokes per minute. Record total pump strokes, drill pipe pressure, and casing pressure. Pump until the casing pressure reaches the pressure required for the formation integrity test. Stop pumping and hold the pressure for a few minutes to confirm pressure stability.
5. Bleed off the pressure and open the well. Then start the drilling operation.