ANALYSIS CHART KEEPS TRACK OF MUD WEIGHT

SECTION 6

ANALYSIS CHART KEEPS TRACK OF MUD WEIGHT

This problem illustrates how to proceed when the decision is made to start weighing up the mud as soon as circulation is resumed - the concurrent method.

One of the ways to keep track of changing mud densities is to record mud density increase on the first line on the graphical analysis chart. When each of these increments of density is reached in the suction pit, the number of pump strokes it takes to displace the drill pipe is added to total strokes displayed on the choke panel and recorded below each appropriate mud density. The choke operator then knows when each mud density reaches the bit. This is the approach used in this problem.

Other methods of keeping track of the mud density in the drill pipe and the resulting necessary changes in the ICP are:

1. Using 3/4 the pump strokes to displace the drill pipe.

2. Adjusting the ICP for the actual mud density in the pits.

While it appears complicated, the method illustrated in this problem takes the least amount of time. It therefore reduces the potential for all the problems with the hole and drilling rig that come with increased elapsed time.

This is a typical oilfield situation about which there seems to be much confusion. But if the choke operator follows simple rules the kick can be killed successfully.

Supervision is important - never let up when there is a well kick.

Problem 6-0

The well was shut in after an increase in pit volume of 50 bbl (8 m³).

The well plan states that you will start circulating immediately and at the same time start increasing the mud density. Trip margin (or safety margin) to be used was given on the well plan as 0.3 ppg (0.4 SG, 2 lb/ft³).

Fill out the blowout control sheet using mud density on the graph.

Depth = 3048 m (10000 ft)

Casting = 9 5/8" at 2987 m (9800 ft)

Hole size = 8.5"

Drill pipe = 4.5"

Mud density = 13.0 ppg (1.560 SG, 97 lb/ft³)

Surface-to-bit = 1400 pump strokes

Displace annulus = 3100 pump strokes

System pressure loss @ 38 spm = 85 kg/cm² (1200 psi)

Pumps run evenly at 38 spm.

Problem 6-1

The choke is opened and the pump has started. The derrick man is mixing barite and the tool pusher has to go answer the radio.

What should you do:

Increase choke size?

Decrease choke size?

Increase pump rate?

Decrease pump rate?

Everything is OK - continue?

Stop the pump and close the well in?

Problem 6-2

Everything is going smooth. The derrickman says that a mud density of 13.1 ppg (1.575 SG, 98 lb/ft³) has been going in the hole since you started the pump.

What should you do:

Increase choke size?

Decrease choke size?

Increase pump rate?

Decrease pump rate?

Everything is OK - continue?

Stop the pump and close the well in?

Problem 6-3

The drilling superintendent is calling. Every time the derrickman informed you of the newer mud densities you faithfully added 1400 to the number of strokes displayed on the pump stroke counter, and recorded same on the work sheet because the rules said to do it. You wish everyone would shut up and let you think.

What should you do:

Increase choke size?

Decrease choke size?

Increase pump rate?

Decrease pump rate?

Everything is OK - continue?

Stop the pump and close the well in?

Problem 6-4

The derrickman calls and says the mud density is 14.3 ppg (1.715 SG, 107 lb/ft³). You have been watching your graph and keeping a general track of time. You recheck - are you correct?

What should you do:

Increase choke size?

Decrease choke size?

Increase pump rate?

Decrease pump rate?

Everything is OK - continue?

Stop the pump and close the well in?

Problem 6-5

You are taking a break and drinking tea. Someone yells and says that the pits are starting to overflow. The derrickman is banging on the bulk hopper. The horn on the radio is blowing. The driller wants to turn the water on the engine exhausts because there is gas under the floor.

What should you do:

Increase choke size?

Decrease choke size?

Increase pump rate?

Decrease pump rate?

Everything is OK - continue?

Stop the pump and close the well in?

Problem 6-6

The pit volume is going down. The casing pressure is going down. Did we lose returns? There is lots of gas at the choke and separator.

What should you do:

Increase choke size?

Decrease choke size?

Increase pump rate?

Decrease pump rate?

Everything is OK - continue?

Stop the pump and close the well in?

Problem 6-7

Choking fine, drinking tea, small amount of gas through separator. Mud density in suction pit has stayed at 14.3 ppg (1.715 SG, 107 lb/ft³). Why has casing pressure not gone to zero?

What should you do:

Increase choke size?

Decrease choke size?

Increase pump rate?

Decrease pump rate?

Everything is OK - continue?

Stop the pump and close the well in?

Problem 6-8

You let a worm engineer take over the controls so you could go to a safe place and smoke a cigarette. That took 5 minutes. Mud density going in the hole is still 14.3 ppg (1.715 SG, 107 lb/ft³). Look what has happened. You find out as soon as you left, casing pressure was allowed to go to zero. There is some gas at the choke and pit volume has stopped going down and has started to increase.

What should you do:

Increase choke size?

Decrease choke size?

Increase pump rate?

Decrease pump rate?

Everything is OK - continue?

Stop the pump and close the well in?

Problem 6-9

The boss has been called and told that kick has been killed.

What should you do:

Increase choke size?

Decrease choke size?

Increase pump rate?

Decrease pump rate?

Everything is OK - continue?

Congratulate yourself on how smart you are and go back to drilling.

ANSWERS

Problem 6-1: Increase the pump rate to 38 spm as required on the well program. Notice that you could kill the well at 1070 psi (75 kg/cm²) and 26 strokes.

Problem 6-2: Everything is OK - continue. Notice that drillpipe pressure is OK while the annulus pressure has gone down. It is not unusual for the annulus pressure to go down a by a small amount after the kick gets above the drill collars. Record 1400 strokes under 1.575/13.2. This is the number of strokes you will see on choke panel when that density mud is at the bit.

Problem 6-3: Decrease choke size. According to your graph the pressure should be about 1690 psi (119 kg/cm²). "Everything OK" could be a correct answer because charts and graphs are difficult to read that accurately.

Problem 6-4: Decrease choke size. Pressure control work sheet shows that at 1690 strokes, pressure should read 115 kg/cm² (1635 psi). If "The Man" will stop calling you on the radio, you will be okay.The derrickman has been able to call you on each increase in density and you have faithfully been recording it on work sheet.

Problem 6-5: Increase the pump rate. You must keep pump strokes constant (or make corrections for pump rate vs. pressure). Keep your cool! The radio will wait. The engine exhausts should have had water in them long ago. Drillpipe pressure should be about 100 kg/cm² (1440 psi) when the pump rate is 38 spm.

Problem 6-6: Everything is OK - continue. Constant pump pressure and rate. Casing pressure decrease is normal. Mud replaced the gas in the hole so the pit volume goes back down."Decrease the choke size" could be the correct answer because we have not quite reached the 3100 strokes. Under actual field conditions no changes would be made.

Problem 6-7: Everything is OK - continue. The formation is still exerting pressure above the hydrostatic head. Notice that it will take about 4500 pump strokes to totally displace the hole.

Problem 6-8: Decrease choke size. The drillpipe pressure should go up to 1320 psi (93 kg/cm²). You have let another gas bubble into the well.

Problem 6-9: Everything is OK - continue. "Congratulate yourself on how smart you are and go back to drilling" is not correct. See problem and answer 6-8.