wellcontrol-basic

7/30/2019 wellcontrol-basic

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1

Basic well control 1

At the end of this lecture, YOU will be able to;

1. Define the term “kick”.

2. State two possible causes of a kick.

3. Calculate the kill mud density for a Balanced kill from

shut in well data.

4. Describe the major difference between a “Balanced”

kill and a “Drillers Method” kill.

5. Explain why the annulus pressure rises when

circulating out a gas kick.



2

Kick - definition

A kick occurs when formation pore fluid flows in to

the wellbore due to insufficient mud hydrostatic

pressure.



3

Kick causes

Drilling in to an overpressured formation

Not keeping the hole full of mud

Swabbing

Mud gradient reduces due to contamination or

poor maintenance

Unplanned disconnect of a marine riser.

Insufficient mud hydrostatic pressure might be caused by:



4

Immediate actions

Kick is detected by

Increase in flow rate

out of the hole

Increase in surfacemud volume

Driller has to close the

Blowout Preventer asap!



5

Overpressure - well closed in



6

What next?

Before normal operations resume;

The influx has to be removed from the annulus

Mud hydrostatic has to balance the formation

dp

dp

Formation pressureMud gradient to balance =

True Vertical Depth

Formation pressure = mud hydrostatic + P

(mud gradient x TVD) + PSo kill mud gradient =

TVD



7

Example

A well kicks. The true vertical

depth of the kicking formation is

10,000’. The mud gradient in

use is 0.6 psi/ft. The well kicksand after closing the BOP, the

drill pipe pressure stabilises at

1,000 psi. What is the formation

pressure and what mud gradientis required to balance it?

dpFormation pressure = mud hydrostatic + P

(10, 000 0.6) 1, 000 7, 000

7,000So kill mud gradient = 0.7 psi/ft

10,000

f P = × + =

=



8

Exercise










8,000’. The mud gradient in use

is 0.5 psi/ft. The well kicks andafter closing the BOP, the drill

pipe pressure stabilises at 400

psi. What is the formation

pressure and what is the kill mudgradient to balance it?


(10, 000 0.6) 1, 000 7, 000


10,000

f P = × + =

=



9

Answer










8,000’. The mud gradient in use

is 0.5 psi/ft. The well kicks andafter closing the BOP, the drill

pipe pressure stabilises at 400

psi. What is the formation

pressure and what is the kill mudgradient to balance it?


(10, 000 0.6) 1, 000 7, 000


10,000

f P = × + =

=


(8,000 0.5) 400 4, 400


8,000

f P = × + =

=



10

Balanced method kill

Also called “wait and weight” method

The well is kept closed in while the surface muddensity is increased.

When kill mud is prepared, it is circulated around

the well in one circulation.

This circulation removes the influx and kills the

well.



11

Drillers method kill

The well is kept closed in while the pressures

stabilise.

When ready, the well is circulated with original

weight mud to remove the influx. Meanwhile kill

mud is prepared.

After completing the first circulation, kill mud is

circulated around to kill the well.



12

Differences between Balanced and Drillers

Balanced Method

Completed in one

circulation. Lower pressures on the

wellbore.

Takes less time overall. Requires calculation of

circulating pressures

throughout the kill.

The preferred method in

most cases.

Drillers Method

Completed in two

circulations. Can be started very quickly

as no weighting up initially.

Easier operationally - onlytwo calculations are needed

(kill mud density and hole

volume).



13

Annular gas expansion

Pressure in the gas

reduces as it rises, so -

Gas expands as it rises(Boyle’s Law), so -

Gas height increases,

mud height decreases.Hydrostatic of gas +

mud decreases, so -

Pan must rise tocompensate if the BHP

stays the same.



14

Annulus pressure rises

Annulus pressure rises when circulating out a gas

kick because gas expansion reduces the height of mud in the annulus.



15

Basic well control 1

Now, YOU should be able to;

1. Define the term “kick”.

2. State two possible causes of a kick.

3. Calculate the kill mud density for a Balanced kill from

shut in well data.

4. Describe the major difference between a “Balanced”

kill and a “Drillers Method” kill.

5. Explain why the annulus pressure rises when

circulating out a gas kick.



16

Any questions before the test?

This is a closed book test. Please put

away your notes and handouts.

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