A KICK CAN BE HANDLED WITHOUT PRERECORDED DATA.

SECTION 5

A KICK CAN BE HANDLED WITHOUT PRERECORDED DATA.

This problem illustrates how a constant circulating pressure and pump rate can be obtained when faced with a situation where no prerecorded information is available. Only shut in values are available.

In this case, you will have to make do with information you can determine. The ICP can be obtained by holding casing pressure constant until the pump is running at some predetermined rate. The pump rate should be about half normal rate.

This problem also shows how quickly things happen when large amounts of gas reach the surface. So once rules or procedures are established, chances of success are greatest if they are followed.

Important points. Notice in 5-3 how the use of constant casing pressure to obtain the ICP could introduce an immediate 100 psi (7 kg/cm²) error into the pressure necessary to control the well. In this case, the error was small, but it could be larger with a deep, slim hole. The original discussion in section 1, under Rule 6, states that constant casing pressure should not be used (or assumed) in deep, slim holes nor when there is gas near the surface. Furthermore, the period of constant casing pressure when starting the pump should be as short as possible.

Problem 5-5 and 5-8 illustrate that there is often a time lag between opening or closing the choke and the resulting change on the drillpipe pressure gauge. The time lag varies from almost nothing to as much as a minute. A standard rule of thumb is to use 1 second per 1000 feet. Remember to include downtime in this.

Problem 5-9 notes one of the problems involved in maintaining a constant pump rate is that large pressure changes may change the pump rate.

Often there is confusion because it appears that the gas reaches the surface earlier than it should. It is necessary to remember that the gas is constantly expanding and so we can expect it to arrive at the surface early.

The constant expansion of the gas causes an increase in the mud volume in the pits. When the gas is circulated out of the hole then the mud is pumped back in to replace it. Often the lowering of the mud volume in the pits is mistaken for lost circulation.

Problem 5-0

Problem Facts:

An increase in flow and pit volume was noticed when the rig was shut down to change pumps. No prerecorded spm, but use 36 spm as kill rate on pumps. With the well shut in, the following is observed: a pit volume increase of 50 bbl (8 m²). Do not increase the mud density until you circulate the gas out of the hole.

Drill pipe = 4.5" 16.60 lb/ft

Depth = 10000 ft (3048 m)

Hole size = 8.5"

Mud density = 13 ppg (1.56 SG, 97 lb/ft³)

9 5/8" casing at 8000 ft (2438 m)

Trip margin = 0.3 ppg (0.04 SG, 2 lb/ft³)

Drill collars = 6 5/8" x 1000 ft (305 m)

Pumps = 6.5" x 16"; 8.6 gal/stroke

(32.6 l/stroke)

Problem 5-1

The choke is opened and pump started, now the choke is slowly being closed. 30 sec after the pump is started, this situation exists.

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 5-2

A short time later this is what was observed.

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 5-3

Five minutes after the pump is started this was observed. Does the drop in casing pressure indicate lost returns? The pit volume totalizer doesn't show much change.

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 5-4

Are you choking up? Remember the rules.

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 5-5

Look what happened just as soon as the choke change was made. Don't panic - let common sense prevail.

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 5-6

Things seem to settle 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 5-7

A lot of noise, kill line frosting up, pits flowing over. The driller is unhappy.

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 5-8

You made your adjustment in problem 5-7. Why has the casing pressure not changed?

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 5-9

Iron begins to rattle, a weird noise is heard as gas begins to go through the separator. Everyone acts as if he were walking on egg shells. You check the pump throttle setting and it has not been moved.

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 5-10

The sound is now more of a shriek rather than noise, and a blueish colour is coming out of the gas separator. Everyone has left the floor except you and the driller. (Run is not on the answer sheet).

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 5-11

Iron has stopped rattling, everything seems quiet. The derrick man says that mud density is 13.0 ppg (1.56 SG, 97lb/ft³ ) at both suction and degasser. Do you go back to drilling? Has all intruding gas been pumped out of the well bore?

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?

7 Open BOP and see if the well flows?

ANSWERS

Problem 5-1: Decrease choke size. Keep closing choke slowly to bring casing pressure up to original shut in casing pressure of 1300 psi (91 kg/cm²).

Problem 5-2: Everything is OK - continue. At this point you have the same pressure against the reservoir as with the well shut in. Now ignore casing pressure and go to constant drillpipe pressure and constant pump strokes. What is your constant pump pressure? Constant pump strokes?

Problem 5-3: Everything is OK - continue. As the gas was pumped up away from the drill collars, the annular area becomes larger and the gas column shorter. This happens once in a while when the gas is in a large bubble on the bottom. ICP is 1600 psi (112 kg/cm²). Constant pump stroke rate is 36.

Problem 5-4: Decrease choke size. The applicable rule is constant pump pressure and constant pump strokes. Drillpipe pressure must be restored to ICP.

Problem 5-5: Everything is OK - continue. Give the pressure time to come around, it may take as much as 1 min before the change shows up on the drill pipe gauge. Run around in tight circles, but don't panic.

Problem 5-6: Everything is OK - continue. You're choking fine; if the casing pressure worries you, put a sack over the gauge.

Problem 5.7: Increase pump rate and then adjust drill pipe pressure to 1600 psi (112 kg/cm²). If you do it quickly enough you might keep another bubble from entering bore hole on bottom.

Problem 5-8: Everything is OK - continue. Casing pressure has not changed because there is also a time lag from drillpipe pressure to casing pressure.

Problem 5-9: Increase choke size - back pressure is stalling the pumps. Opening the choke will let the pump pressure drop and let the pump go back to 36 strokes per minute."Everything is OK" could be a correct answer because at this point you are steadily opening the choke and it is hard to keep up.In some cases, especially when a large bubble has intruded, pump rate tends to change because of the rapid change in back pressure against the pumps when bubble and maximum pressure are at the surface. Well killing experts with practical experience advise that adjusting casing pressure to keep drillpipe pressure constant restores the pump to the desired rate. Changing previously established throttle setting here upsets all the parameters. NOTE: Most of the time, when control of kicking well is lost, control is lost at this point because too many things are happening at the same time.

Problem 5-10: Everything is OK - continue. Don't forget that there is a lot of gas that you need to vent to the atmosphere. Don't light up a cigarette.

Problem 5-11: Well is not dead. Probably some gas is entrained in the mud but the bubble is out of the hole. Notice that the circulating casing pressure is lower than you might think. Ordinarily, you would expect it to be 500 psi (35 kg/cm²). In this case, however, the annular pressure loss may be causing an apparent lower circulating pressure.