SECTION 3
DON'T RULE OUT PUMP TROUBLES DURING A KICK
Problems in the first section of this manual assumed that the system pressure loss had been prerecorded by the crew. The problems presented here illustrate another method of determining system pressure loss.
While the prerecorded method is more desirable, it may not always be available. In this case, the annulus pressure may be held constant for a short period while the pump is brought to some desirable circulating rate. At that time, the pump pressure will be the sum of the system pressure loss and the shut in drillpipe pressure.
The circulating system is the same as that 12212y241m used in the previous sections.
Key points. The key to killing a well is maintaining a constant bottom hole pressure using constant drillpipe pressure and constant pump rate. The drillpipe pressure and pump rate may be established in different ways. But however they are determined, the key to well control is still constant drillpipe pressure and constant pump rate.
In this problem, a washed-out pump valve is used to illustrate the method of changing pumps.
The key to a pump problem in this case is the erratic movement of the kelly hose.
Do not assume that casing pressure will stay constant under any conditions. It is best to use constant casing pressure for as short an interval as possible and only when a prerecorded pressure is not available.
Use of constant casing pressure is a "make-do" method and should be used only if it is the only tool available.
Try always to use a pressure control work sheet. Without one, it is very difficult to remember all the numbers during a well kick.
Problem 3-0
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Problem Facts:
In problem 2 we saw that the casing pressure was constant if the weight of the mud column in the annulus did not change. We can use this fact to find the initial circulating pressure or to check calculations of initial circulating pressure. We can also use it to check or replace the graphical analysis.
The well kicked and is now shut in. Fill out the pressure control worksheet. Do not raise mud density until the kick is circulated out of the hole.
Depth = 12000 ft (3650 m)
8.5" hole with 4.5" drill pipe
Kick size = 5 bbl (0.8m3)
Mud density = 10 ppg (74.8 lb/ft3, or 1.2 SG)
System pressure loss @ 30 spm - 740 psi (52 kg/cm2)
1050 pump strokes to displace drill pipe
2300 pump strokes to displace annulus
Use 0.3 ppg (2.0 lb/ft3, or 0.04 SG) for annular pressure loss
Complete the pressure control worksheet.
Problem 3-1
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When starting to circulate, you are going to hold the casing pressure constant until the pump gets up to 30 spm. Then you will check to see if your calculated ICP and the actual ICP are the same. If they are, continue. If not, shut in the well and find the error.
Remember, we are not raising the mud density.
Now after 15 pump strokes or half a minute you see this.
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 3-2
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While the driller is answering the radio 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 3-3
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You are having trouble with the torque-converter drive to the pumps, but look at this closely.
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 3-4
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What is wrong now - everything is going down.
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 3-5
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Everything looks OK, but the casing pressure went down slightly.
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 3-6
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Pump strokes going up, pressure going down. The kelly hose is jumping. Make a decision!
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 3-7
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You closed the well in and switched over the No. 2 pump. It has 6.5" liners instead of 6" liners. You are ready to start up.
What should you do:
1 Start up to 30 spm?
2 Calculate a new pump rate?
3 Start up and hold drill pipe pressure constant
4 Start pump and hold casing pressure constant?
5 Call Halliburton and Red Adair?
6 Call the vice-president for drilling and production?
Problem 3-8
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You and the toolpusher decide that the circulating rate should be 28 spm. Can you do that? Have you got everything wrong?
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 3-9
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Have you done the wrong thing? The casing pressure is going up. Should you do something else to be safe?
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 3-10
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Casing pressure went to 600 psi (42kg/cm2). What should you do? Have we lost circulation? The pit volume has decreased, but is now holding constant.
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?
ANSWERS
Problem 3-0: See completed pressure control work sheet (Fig 3-1).
Problem 3-1: Increase the pump rate to 30 spm. Keep the annulus pressure constant by changing choke size.
Problem 3-2: Decrease the pump rate. You had planned to run at 30 spm. What would be the ICP at 37 spm if it was necessary to use that rate?
Problem 3-3: Decrease the pump rate. Then you may have to open the choke. Notice that the pump rate is too high, but the annulus pressure has gone up. You may have two problems, but solve them one at a time. Slow the pump first, then see if you need to open the choke more.
Problem 3-4: Everything is OK. Notice that the calculated ICP and the actual ICP are the same at 30 spm. The annulus pressure is still at the shut in value. Good show! Now switch to drillpipe pressure and use the ICP as your constant drillpipe pressure.
Problem 3-5: Everything is OK - continue. You are using constant drillpipe pressure as your control now. If you do not understand why, go back and review.
Problem 3-6: Stop the pump and close in the well. You cannot kill a well if the pump rate is not constant. The increase in pump rate and decrease in drillpipe pressure means either a hole in the drill pipe or a bad pump. The jumping kelly hose indicates the problem is at the pump.
Problem 3-7: Start No. 2 pump and hold casing pressure constant. If you do not understand this key lesson, go back and review.
Problem 3-8: Everything is OK - continue. You keep casing pressure constant until you reach a predetermined pump rate. The new "constant drillpipe pressure "is 1500 psi (105 kg/cm²) at 28 spm on no. 2 pump. You can pick any pump rate or pressure provided the rig will operate smoothly under those conditions.
Problem 3-9: Everything is OK - continue. The casing pressure will rise as the bubble comes to the surface. If you reduce the casing pressure, you will let more gas into the hole. Remember, using this technique, we use a constant casing pressure to get the constant drillpipe pressure. Casing pressure is not a "control" for killing the well.
Problem 3-10: Everything is OK. You are now ready to increase the mud density; or stop the pump and shut in the well. You should have the gas displaced out of the hole. When the gas comes out of the hole and is displaced by mud, the pit volume decreases. If you think you might have lost circulation, go see if the mud is still circulating.
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