SECTION 4
GRAPHICAL METHOD PLOTS PUMP STROKES
This group of problems continues section 3. It illustrates the use of the graphical procedure for deducing drillpipe pressure when increasing mud density.
Key points. When the graphical procedure is used, time and pump strokes should be plotted against pump pressure. Pump strokes is the best term to use.
Notice that the casing pressure stays relatively constant while the new heavier mud is filling the drill pipe. The assumption that casing pressure will always stay constant under these conditions may be incorrect.
Problems discussed to date in this manual cover the basic elements of well control. These problems should be completely understood before proceeding to solve those in the remainder of 222n1315c the series. Problems in following sections will involve more sophisticated versions of the information already presented.
Problem 4-0
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You have pumped the gas kick out of the hole in Problem 3. Now it is time to increase the mud density. Use the pressure control work sheet from Problem 3 (Fig 3-1). Switch back to the No. 1 pump - the valve has been replaced.
When the new mud is going down the drill pipe, hold casing pressure constant and compare the drill pipe pressure with the graphical analysis.
Zero the pump counter.
You are ready to start when the mud density in the pits is 11.3 ppg (85 lb/ft3, or 1.35 SG).
Problem 4-1
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After 210 pump strokes (7 min) you have this situation.
What should you do:
1 Increase choke size?
2 Decrease choke size?
3 Increase pump rate?
4 Decrease pump rate?
5 Everything is OK - continue?
6 Stop the pump and close the well in?
Problem 4-2
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As the new mud goes down the drill pipe, the drillpipe pressure goes down. The casing pressure is going up.
What should you do:
1 Increase choke size?
2 Decrease choke size?
3 Increase pump rate?
5 Everything is OK - continue?
4 Decrease pump rate?
6 Stop the pump and close the well in?
Problem 4-3
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This is a critical point. What must you do and why?
What should you do:
1 Increase choke size?
2 Decrease choke size?
3 Increase pump rate?
4 Decrease pump rate?
5 Everything is OK - continue?
6 Stop the pump and close the well in?
Problem 4-4
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Casing pressure is still holding constant. Are we still okay?
What should you do:
1 Increase choke size?
2 Decrease choke size?
3 Increase pump rate?
4 Decrease pump rate?
5 Everything is OK - continue?
6 Stop the pump and close the well in?
Problem 4-5
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You were drinking a cup of coffee - and look what happened!
What should you do:
1 Increase choke size?
2 Decrease choke size?
3 Increase pump rate?
4 Decrease pump rate?
5 Everything is OK - continue?
6 Stop the pump and close the well in?
Problem 4-6
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Casing pressure is almost zero. The mud man says the barite is almost gone. It looks like we are in trouble. Driller says slow the pump down to make the barite last.
What should you do:
1 Increase choke size?
2 Decrease choke size?
3 Increase pump rate?
4 Decrease pump rate?
5 Everything is OK - continue?
6 Stop the pump and close the well in?
Problem 4-7
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The tool pusher is in a hurry to make the short trip because the Wireline logger is on the way. Casing pressure is zero.
What should you do:
1 Increase choke size?
2 Decrease choke size?
3 Increase pump rate?
4 Decrease pump rate?
Everything is OK - continue?
6 Stop the pump and see if the well will flow?
Problem 4-8
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You stopped the pump but the well continued to flow a small stream. You shut in and this is what the gauges indicate.
What should you do:
1 Make the short trip?
2 Circulate the hole with 30 strokes at
840 psi (59 kg/cm2)?
3 Increase mud weight in the pits?
4 Decrease mud weight in the pits?
5 Increase mud weight slightly and
circulate as in 2 above?
6 Call for help?
ANSWERS
Problem 4-0: See pressure control work sheet (Fig 3-1).
Problem 4-1: Everything is OK - continue. Pump strokes is a more positive measure than time. You know your calculations are correct because casing pressure is 600 psi (42 kg/cm2), ie the shut in value, and the drillpipe pressure is the same as on the chart, or 1250 psi (88 kg/cm2).
Problem 4-2: Open the choke. The casing pressure has gone up and you are above the line on the graphical analysis. You are putting too much pressure on the formation.
Problem 4-3: Everything is OK - continue; or the pump can be stopped and the well closed in. The drill pipe is full of the heavy mud. If you stopped the pump and shut the well in, the shut in drillpipe pressure would be zero. Now keep the drillpipe pressure constant while the new mud goes up the annulus.
Problem 4-4: Open the choke. You should be keeping the drillpipe pressure constant - not the casing pressure. When holding casing pressure constant, be sure you know what you are doing and when you should do it.
Problem 4-5: Everything is OK - continue. The casing pressure is expected to come down as the heavier mud fills the annulus.
Problem 4-6: Increase the pump rate. If you get sloppy now, you will get another bubble in the hole and have to make another circulation. Better order more barite.
Problem 4-7: Stop the pump and see if the well will flow.
Problem 4-8: Either answer 2 or answer 5 is appropriate. The hole can be circulated with 30 spm and 840 psi (59 kg/cm²), or the mud weight can be increased slightly and circulated with a new circulating pressure.The situation shown here happens often. The SIDPP may not have reached its highest value because of low permeability. It is also possible that you misread the gauge or that it was inaccurate. On the other hand there may still be some gas in the annulus.Too bad about the logging truck being on the way, but if you come out of the hole now, you may have a blowout.
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