Casing Seat Test Procedure Leak off test

  1. Drill out cement plus ca. 20 ft of formation
  2. Circulate and condition mud
  3. Pull the bit back in casing shoe
  4. Make sure the hole is filled up and close the BOP around the drillpipe
  5. Pump mud slowly using a high pressure low volume pump until the pressure builds up. Calibrated pressure gauges, covering various pressure ranges and preferably mounted on a special manifold, should be used. Mud gauges are not accurate enough for these measurements. Rig pumps are unsuitable for carrying out casing seat tests.
  6. Then pump 0.1 bbl and wait for 2 minutes or the time required for the pressure to stabilize in the case this takes longer.
  7. Note the cumulative mud volume pumped, the final pumping and final static pressure.
  8. Repeat items 6 and 7 plot pressures versus cumulative mud volume for each pumped volume increment.
  9. Continue procedure until the final pump pressure deviates from final static pressure after the waiting time or until a predetermined pressure has been reached.
  10. Keep well closed in to verify that a constant pressure has indeed been obtained.
  11. Bleed off pressure and establish volume of mud lost to the formation.

From the procedure outlined above it can be seen that during a formation strength test the formation should not be fractured. The point on the pressure versus volume plot which is characterized by a deviation between the final pump pressure and the static pressure after the waiting time is called the "formation intake pressure".

Guidelines for Casing Seat Testing

A. Testing of surface casing seats

Test in all wells by closing BOP's around drillpipe and pressurized casing (up to a maximum of the burst pressure of the casing, taking into account appropriate safety factors).

B. Testing of intermediate casing seats

Test with annulustothe next casing open and full and observe for returns.

Exploration wells: Test all wells (in critical wells every 1000 ft).

Appraisal wells: Test all wells, unless it is known that abnormal pressures are absent or in known territory where less competent rock will be encountered deepter.

Development wells: Test all wells, unless there is a special reason for omitting the test. An intermediate casing is set in development wells for a particular purpose, i.e. casing off troublesome formation(s), abnormal pressures, special completions (liner, open-hole gravel pack, barefooted, etc.). Consequently testing of the casing set is justified in a vast majority of wells, especially offshore.

C. Testing of the production string seat

This casing is not normally drilled through. However, if drilling has been or has to be done below this string, testing should be carried out as under B., since the production string has now become another intermediate casing. A retrievable packer should be used to avoid pressurized this string (which may result in the creation of micro-annuli in the cement).

D. Testing prior to abandonment

In wells drilled in new areas or in those cases where additional regional information is valuable, consideration should be given to carrying out a breakdown test using a cement retainer for squeezing below the casing shoe. Thus useful information on breakdown pressures can be obtained which can be compared with previous data from casing seat tests.

In addition, depending on the type of operation and local regulation, the use of a cement retainer may save thime by eliminating waiting on cement or "feeling" for the plug. If acceptable to local authorities cement can be squeezed through the retainer for abandonment after the casing seat test has been completed.

CASING SEAT TESTS Schematic Representations unconsolidated plastic formations

cumulative volume Figur* 1

cumulative volume Figur* 1

consolidated permeable formations

cumulative volume Figur* Z

consolidated formations low or impermeable cumulative volume FigurĀ« 3

consolidated formations

"limit test"

DESIRED TfST PRESSURE

limit test cumulative volume Figura 4

o final pump pressure after each increment x final pressure after waiting period (T) formation intake pressure

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Responses

  • Amedeo
    When should a leakoff test be carried out?
    1 year ago

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