SECTION 9
RECORD IMPORTANT IN KILLING DEEP WELL
The time it takes to kill a deep well causes most of the problems. People get tired and forget what the plan involved. Equipment may fail because of the stresses put on it over an extended period.
Key points. It is difficult to tell a gas kick from a saltwater flow in a deep well. You must assume that it is gas.
Variations in annular pressure may be the result of choke manipulation, change in annular size, gas expansion, or annular pressure drop.
It is difficult to keep track of what is going on unless a written record is kept.
When in
doubt, stop the pump and shut the well in. Then think about your problem.
There is too much at stake in a well killing operation to continue if you do
not understand what is happening. 
The numbers given on bubble length in the problem are not important for the solution, but are used to explain casing pressure variations.
9.1 PROBLEM 9
Problem 9-0
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Problem facts:
While drilling at 25000 ft ( 24324o147y 7620 m) a gain in pit volume of 15 bbls (2.4 m3) was noticed. The well was closed in. Do you know how to check to see if the drillpipe pressure is correct?
Mud density = 13 ppg (1.56 SG, 97 lb/ft3)
Casing = 7" at 22000 ft (6705 m)
System pressure loss at 30 spm = 1100 psi (77 kg/cm2)
Annular pressure drop at 30 spm = 400 psi (26 kg/cm2)
There are 1500 bbl (236 m3) of mud in the standby tanks with a density of 15 ppg (1.8 SG, 112 lb/ft3)
It requires 3550 pump strokes to displace the tapered string of drill pipe.
The pump is rated at 4000 psi (280 kg/cm2).
Fill out the pressure control work sheet.
Do not add a safety margin (trip margin) to the mud weight required.
Problem 9-1
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Two min later you notice these pressures. Why did casing pressure drop to 2800 psi (197 kg/cm2)?
What should you do:
1 Increase choke size?
2 Decrease choke size?
3 Increase the pump rate?
4 Decrease the pump rate?
5 Everything is OK-continue?
6 Stop the pump and close the well in?
Problem 9-2
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Fifteen min later, after pumping 40 bbls (6.3 m3) of 15 ppg (1.8 SG, 112 lb/ft3) mud down the drill pipe, you notice these changes. What is happening?
What should you do ?
1 Increase choke size?
2 Decrease choke size?
3 Increase the pump rate?
4 Decrease the pump rate?
5 Everything is OK - continue?
6 Stop the pump and close the well in?
Problem 9-3
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The drillpipe pressure is still dropping. Are you choking properly? What is happening to the casing pressure? Do we have the proper back pressure applied to contain the reservoir?
238 bbls (38 m3) of 15 ppg (1.8 SG, 112 lb/ft3) mud has been pumped into the drill pipe.
What should you do?
1 Increase choke size?
2 Decrease choke size?
3 Increase the pump rate?
4 Decrease the pump rate?
5 Everything is OK-continue?
6 Stop the pump and close the well in?
Problem 9-4
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After about 2 hours the drill-pipe pressure is down to 1270 psi (89 kg/cm2). Why? The casing pressure has increased slightly. Why?
What should you do?
1 Increase choke size?
2 Decrease choke size?
3 Increase the pump rate?
4 Decrease the pump rate?
5 Everything is OK-continue?
6 Stop the pump and close the well in?
Problem 9-5
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The casing pressure is going down. Why? Where is the intruding fluid now? Did you lose returns?
What should you do?
1 Increase choke size?
2 Decrease choke size?
3 Increase the pump rate?
4 Decrease the pump rate?
5 Everything is OK - continue?
6 Stop the pump and close the well in?
Problem 9-6
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The casing pressure has to be going up if it is gas. You bet your pay check you either lost returns or it is salt water.
What should you do?
1 Increase choke size?
2 Decrease choke size?
3 Increase the pump rate?
4 Decrease the pump rate?
5 Everything is OK-continue?
6 Stop the pump and close the well in?
Problem 9-7
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What is happening to the casing pressure? You are planning where you will spend all that extra money - some fool has taken you up on that bet. Notice how long you have been pumping. More than 5 hours.
What should you do?
1 Increase choke size?
2 Decrease choke size?
3 Increase the pump rate?
4 Decrease the pump rate?
5 Everything is OK-continue?
6 Stop the pump and close the well in?
Problem 9-8
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All of a sudden the casing pressure increases and nothing but gas is coming out of the separator.
What should you do?
1 Increase choke size?
2 Decrease choke size?
3 Increase the pump rate?
4 Decrease the pump rate?
5 Everything is OK-continue?
6 Stop the pump and close the well in?
Problem 9-9
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The casing pressure goes to 0. Did the formation break down or is the well dead? Has the heavy mud been circulated around yet?
What should you do?
1 Increase choke size?
2 Decrease choke size?
3 Increase the pump rate?
4 Decrease the pump rate?
5 Everything is OK-continue?
6 Stop the pump and close the well in?
Problem 9-10
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At this point you have pumped 1260 bbl (200 m3) of 15 ppg (1.8 SG, 112 lb/ft3) mud which has completely displaced the intruding fluid and the old mud. Can you open the blowout preventers?
What should you do?
1 Increase choke size?
2 Decrease choke size?
3 Increase the pump rate?
4 Decrease the pump rate?
5 Everything is OK-continue?
6 Stop the pump and close the well in?
Problem 9-11
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You started out of the hole for a short trip. After six stands of pipe were pulled, the hole would not take any mud.
What should you do?
1 Continue the trip
2 Shut the BOP
3 Go back to bottom and circulate
4 Go back to bottom and increase the
mud density 0.3 ppg (0.034 SG, 2lb/ft3).
9.2 ANSWERS
Problem 9-0: See pressure control work sheet.
Problem 9-1: Everything is OK - continue. Follow surface-to-bit chart for proper drillpipe pressure corrections. 118 minutes and 3550 strokes later you will have new mud down to the bit.
Remember the casing pressure will drop while circulating an amount equal to the annular pressure loss which at 30 spm is 400 psi (28 kg/cm2).
Problem 9-2: Everything is OK - continue. The drillpipe pressure is reacting according to the chart. The pump strokes are constant at 30 spm. The casing pressure is lower because the length of the gas bubble in a 6" hole with 3½" drillpipe is 773ft (234 m) compared with 980ft (296 m) with 4¼" drill collars in 6" hole.
Often the casing pressure will go down when you start pumping on a kick.
Problem 9-3 Everything is OK - continue. Drillpipe pressure is still following chart. Casing pressure is lower because intruding fluid is in the 9_" casing, with 3½" pipe and length of gas bubble is 249 ft (82 m) compared with 980 ft (296 m).
Remember that the casing pressure will go up slightly when intruding fluid gets around 5" drill pipe.
Problem 9-4: Everything is OK - continue. The drillpipe pressure is at the FCP. Keep the pump strokes and the drillpipe pressure constant until 15 ppg (1.8 SG, 112 lb/ft3) mud is at the surface.
The casing pressure increased because the gas column is longer.
Problem 9-5: Everything is OK - continue. The bottom of the fluid entry is now at 6000 ft (1829 m), the top of the new mud is at 12000 ft (3658 m). Ordinarily you would not be concerned with these values.
The gas has not begun to expand very much yet. The heavy mud is now in the annulus and is starting to reduce the casing pressure.
Problem 9-6: Everything is OK - continue. Which way are you betting?
Problem 9-7: Everything is OK - continue. This is a deep hole and it takes a long time to circulate.
Problem 9-8: Increase the choke size. The pump rate will probably go up to 30 spm when you reduce the pressure or as the engine governors stabilize. The sudden increase in pressure accounts for the lower pump rate. This is where you generally have trouble when killing a deep well. You have been pumping for 5½ hours and everyone is bored and tired. You got careless because you thought it was salt water. It is hard to tell gas from salt water in a deep well until it gets to the surface.
Problem 9-9: Everything is OK - continue. The intruding fluid has been circulated out of the hole. The well is under control as long as you continue circulating. The heavy mud must reach the surface before the well is dead.
If you stop circulating at this point and shut the well in you would notice about 200 psi (14 kg/cm2) on the casing pressure gauge. The annular pressure loss when circulating at 30 spm is providing the back pressure needed until the heavy mud is around.
Problem 9-10: Everything is OK - continue. The mud should be 15 ppg (1.8 SG, 112 lb/ft3) at the separator.
It would be OK to open the blowout preventers and circulate through the flow line. Under static conditions the formation pressure is balanced by the column of heavy mud.
Problem 9-11: Go back to bottom and increase the mud density 0.3 ppg (0.034 SG, 2 lb/ft3). You forgot to add the trip margin to the mud weight before you started out of the hole. The reservoir gas was swabbed in behind you.
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