should be performed to determine the fracturing pressure without breaking down the formation.
When the formation integrity test is required, the maximum pumping pressure is often expressed in terms of “Equivalent Mud Weight” (EMW), which is as under
Leak off or formation integrity test can be carried out at any time while drilling the hole. For instance, the casing seat can be in shale and the first sand formation may be encountered several hundreds of feet deeper. This will certainly be more permeable than the shale and a test can be performed to ascertain the maximum pressure this sand can hold. If it is lower than the shale just below the casing seat, this sand becomes the limiting factor.
Prior to performing a test, keep a sheet of graph paper, pencil and ruler ready for use.

5.2 LEAK-OFF TEST PROCEDURE

1) Drill out float equipment, clean rat hole and drill 5 m (15 ft) of new hole.
2) Circulate hole clean and condition the mud to ensure that the mud weight “IN” and “OUT” is in balance.
3) Pull the bit back into the casing shoe.
4) Make up cementing line to drill pipe. The cementing unit shall be equipped with high precision low
pressure gauges. The range of pressure gauge shall be selected based on the actual mud weight and
the estimated (LOT) or predetermined (FIT) pressure. A pressure recorder with chart should be used
during the test. Rig pumps are unsuitable for making these tests.
5) Fill and test the line with mud.
6) Break circulation with cementing unit to make sure that the bit nozzle is clear and stop pumping when the circulation is established.
7) Close top pipe rams or annular.
8) Open annulus of previous casings.
9) Pump slowly until pressure builds up.
10) Once pressure is established, pump uniform increments of 0.25 bbls (for 12-1/4” and smaller holes) or 0.50 bbls (for 17-1/2” holes) and wait for two minutes, or the time required for the pressure to stabilize if this takes longer.
11) Note the cumulative mud volume pumped, the final pumping and final static pressure.
12) Repeat steps 8 and 9 and plot pressure versus cumulative mud volume for each increment of pumped volume
13) Continue this procedure until:
-Two points on the plot are reached where the pressure deviates and falls below the approximate
straight line. The point on the plot where the curve begins to bend away from the straight line is called the Leak-Off Point.
or
-The predetermined test pressure is reached.
14) Stop pumping and allow the pressure to stabilize (usually stabilization is reached in 15 minutes).
15) Bleed off the pressure and record the quantity of fluid returned into the cementing unit.
16) Open BOP and calculate the formation strength test in terms of “Equivalent Mud Weight” using the lowest among leak off point pressure and stabilized pressure.

6 ATTACHMENTS

Example of Leak-Off Test Plot Interpretation