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The CLEAN-UP period

The purpose of the clean-up period is to eliminate all foreign fluidssuch as mud filtrate, completion fluids, etc., contained in the invadedzone and the well bore so that representative reservoir fluids may be

produced during the test. The flow rate during clean-up should be thehighest rate compatible with well equipment and reservoircharacteristics. Sand breakthrough, water coning, etc. should beavoided.

In the case of a gas well, the drawdown normally should not eceed25% of the static well head pressure.

!urthermore, gas velocity in the well head should not eceed "#ft$sec.

In practice, the formation productivity is rarely known before the testbut a first estimation may be obtained during the clean-up period bymeans of a choke performance chart.%hoke performance charts for oil and gas are available in the practicaltables book, or !&' (.)lthough assumptions are necessary, these estimated flow rates can behelpful when planning the flow rates for the actual test sequence.

If no better information is available, assume the following*

If +& is unknown in an oil well* +& scf$bl/ #.( 0epth ft/

If +& is greater than "### scf$bl* This is a +as well

) well testing program should then be established in accordance with*

- The nature of fluids produced oil orgas/,

- The reservoir characteristics high, low productivity/.

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Estimation of the duration of the CLEAN-UP period

The following criteria should be used to estimate if the well is producingclean hydrocarbons and if the dean-up may be ended.

(.asic Sediment and 1ater measurement.

- S1 is less than ( 2 if solids are still present.

3.Salinity measurement on produced water or S1.

- Salinity is equal to the salinity of the formation water - otherwise,there is still filtrate in the produced fluid.

4.)fter acid 5ob, p' measurement on produced water or S1 water.

- p' should be neutral p' 6/&therwise, there is still acid in the produced fluids.

7.Stabilization of well head pressure.

- This condition is especially important for +as wells to make surethat wellbore is free of any liquid.

".Stabilization of downhole pressure.

-

1hen surface read-out is available.

8.9isual eamination of the flare

- 1hite or +rey smoke may indicate the presence of water in thewell effluent. !ast changes at the flare indicates the venue of surgesof water.

6.:inimum amount of fluids has been produced.

- In all cases, it is necessary to produce a volume of fluid at leastequal to the well bore volume.

;.Surface flow rate stabilization.

This is a good indication that near borehole part of the reservoirand perforations have been cleaned of foreign solids.