3 1 well control

Basic Well Control• Lecture Objectives • Define the term “kick”, • State warning signs of a kick, • Describe the drawback of uncontrolled kicks, • State primary and secondary control pro

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Network of Excellence in Training

Basic Well Control

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• Lecture Objectives

• Define the term “kick”,

• State warning signs of a kick,

• Describe the drawback of uncontrolled kicks,

• State primary and secondary control procedures,

• List well killing procedures and the various calculation to fill-up the well control work sheet.

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• Introduction;

exceeds the mud hydrostatic pressure,

the wellbore,

immediate action to bring the well under control.

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• Introduction;

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• Introduction;

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Causes of Kicks

1 Tripping

2 Drilling into an

overpressured zone

3 Failure to fill hole

4 Inadequate mud weight

5 Gas cut mud

6 Lost circulation

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A study of 55 blowouts during a 10-year period lists the following primary causes of blowouts:

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Mud hydrostatic pressure

Pf

Pressure Changes During A Kick Basic Well Control

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Pf

New heavy mud

Pressure Changes During A Kick Basic Well Control

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Pf

Imagine we applied a surface pressure of

Pf – hydrostatic = say

100 psi on surface

100 psi

Pressure Changes During A Kick

Bottomhole pressure changes

by same amount

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Pdp = Pf- mud hydrostatic

Pf

During a kick the reverse happens…

downhole pressure is seen at surface

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Before normal operations ca resume:

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• Primary Control;

formation fluids into the wellbore by keeping sufficient hydrostatic pressure,

• Low mud weight,

• Reduction of the mud column.

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• Primary Control;

• The mud weight maybe too low for the following reason:

– Drilling through an overpressured zone that required a

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• Primary Control;

• This is due to the following scenarios:

– Swabbing:

» This is the process by which the drillpipe acts as a

piston upward,

– Lost circulation:

» This occurs when a fractured formation is being drilled,

it can be either natural or induced fractures

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• Flowrate increase:

– While the mud pumps are circulating at a constant rate, there

should be a constant flowrate of mud returns to surface,

– If the flowrate increases, this will be an indication that

formation fluids are fed into the wellbore

• Pit Volume Increase:

– When active pit level increases This will be a sign that an

influx has been entered the wellbore,

– The influx volume is equal to the pit gain and should be

noted for later calculations

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• Warning Signs of Kicks;

– Primary Indicators:

• Flowing Well with Pumps Shut-off:

– When rig pumps are not operating, there should be no returns,– If the well flows, a flow check must be carried-out to verify whether it is due to either thermal expansion, U-tube affect, or an influx.

• Improper Hole Fill-Up During Trips:

– The hole should be filled when the pipe is tripped-out,

– If the pipe displacement volume has not been replaced, then this

will indicate that the mud has been displaced by the formation fluids.

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• Warning Signs of Kicks;

• Change in Pump Pressure & Flowrate:

– An entry of an influx to the wellbore will reduce the mud hydrostatic pressure and hence the pump flowrate will increase

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Once Kick is Detected by;

hole

volume ( pit volume)

Driller has to close Blowout Preventer

ASAP

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• Secondary Control;

• For a kick detected while drilling:

– Raise kelly above rotary table until tool joint appears,

– Stop mud pumps,

– Close Annular Preventer (or Pipe Rams),

– Record SIDPP, SICP and Pit Gain

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In the 55-well study referred to earlier, evidence showed that after the wells kicked, 62% were not controlled for the following reasons:

Improper well, casing and cementing

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– Interpretation of Shut-in Pressures:

• Shut-in Drill Pipe Pressure (SIDPP):

SIDPP + G m D = BHP

– Where,

BHP = Bottomhole pressure (psi),

Gm = Mud gradient (psi/ft),

D = True vertical depth (ft).

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– Interpretation of Shut-in Pressure:

• Shut-in Casing Pressure (SICP):

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• Kill Mud Weight (Gk)

Gk = Gm + [ (SIDPP + S ) / D ]

– Where,

S = Overbalance normally is 50 to 200 psi

– Care must be taken not to weight up the mud above the

formation fracture gradient

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• Maximum Allowable Annular Surface Pressure (MAASP):

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• Reduced Circulating Rate Pressure (RCRP);

– RCRP is required due to the following:

» To avoid breaking down the formation,

» To have a lower pressure drop due to friction

– Two slow rates are involved:

» PC1 : which is a kill rate (1- 4 BPM is recommended) Initially, the standpipe pressure will be (SIDPP + PC1),

» PC2 : this is the pressure drop due to circulating the heavier mud,

P C 2 = P C 1 x ( G k / G m )

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Migration ( percolation ) rate ( Ft/hr)

= Pressure increase per hour ( Psi/hr) / Mud gradient ( Psi/ft ) New MAASP ( Psi)

= [ Max allowable mud wt (PPG) - mud wt (PPG)] x 0.052 x

Casing TVD (ft) Barite required to raise mud weight ( Lbs/bbl.)

= [1500 x ( Kill mud wt (PPG) - Old mud wt (PPG)] / [ 35.8 - Kill

weight mud (PPG)]

Shut in casing pressure ( Psi)

= Formation pressure (Psi) - [Mud grad x height +

Influx grad x Influx height ] Where Gradients = Psi/ft , Heights = (ft).

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New Pump pressure

= Present pressure ( Psi) x [New SPM / Old SPM ] 2

Pump output ( Bbls/min.)

= Pump liner capacity ( Bbls/Stroke) x Pump speed ( SPM )

Annular velocity ( ft/min.)

= Pump output ( Bbls/min) / Annular Volume ( Bbls/ft.)

Circulation Pressures

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• Well Killing Procedures;

• The method is used when there is no drillstring in the hole,

• This method uses gas expansion to keep BHP greater than

formation pressure,

• Surface pressure is adjusted by bleeding off at the choke in

small amount,

• The drillstring is run into the well while keeping the BOP

closed all time (this procedure is known as stripping-in).

• Once the influx is out of the hole, a heavier mud is then

circulated through drillstring.

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• Well Killing Procedure;

– Wait and Weight Method (Engineer’s Method):

• This method is executed in one circulation,

• While the well is kept closed-in the kill mud weight is prepared on the

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• This method is divided into the four phases:

– Phase 1: Displace drillstring to a heavier mud,

– Phase 2: Pumping heavy weight into the annulus until influx reaches the choke,

– Phase 3: The time taken for all the influx to be expelled from the annulus,

– Phase 4: Stage between all the influx being removed and the

heavy mud reaching the surface

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Annular Gas Expansion: Conclusions

• Gas expands as it rises (Boyle’s Law)

• Gas Pressure reduces as it rises

• Gas height increases, mud height

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Annulus Pressure Rises

Annulus pressure rises when circulating out a gas kick because gas expansion reduces the height

of mud in the annulus.

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• This method is executed in two circulation,

• The well is kept closed-in while the pressures stabilize,

• One circulation to expel the influx, ( meanwhile kill mud

weight is prepared),

• The second circulation with the kill mud is pumped around

the wellbore to kill well.

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• Wellbore and surface pressures are

generally lower with the Weight method, particularly if the influx contains gas.

Wait-and-• The maximum pressure exerted on

the last casing shoe, which is assumed to be the weakest point in the hole, is lower with the Wait-and- Weight method as long as the open hole annular volume is larger than the drillstring capacity,

• The well is under pressure for the

least time and there is less time Features of The W&W Method

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• It requires the longest waiting

time prior to circulation

• If the annulus was full of cuttings

at the time the kick was taken there may be a danger of packing off.

• Gas migration may become a

problem while waiting for the mud

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Differences between Methods

Wait & Weight

Drillers Method

• Completed in two circulations

• Higher pressures on casing shoe

• Must be used in HPHT wells

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• While drilling 6 1/2” hole at 8000’ TVD, a pit gain of 10

bbls occurs The well is shut-in and the following pressures were recorded:

– SIDPP = 600 psi,– SICP = 800 psi.

• The BHA consists of 600’ of 4 3/4” OD DC, plus 3 1/2”

DP Last casing shoe is at 7000’,

• Mud weight is 10.2 ppg, fracture gradient is 0.765 psi/ft.

• Identify; the influx, calculate MAASP, and kill mud weight

using 200 psi overbalance.

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Well is shut in with the following data

Mud Weight in use is 11.0 ppg.

Pump is a National 12-P-160, using 6 ½” liners

Pump output is 0.119 bbl/stroke

Slow Circulating Rate Pressure is 500 psi at 30 spm.

Example

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1 What is the formation pressure ?

mud has reached the bit?

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• Kill Sheet

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(1) What is the kill mud weight required to balance formation pressure?

(4) What is the total annular volume? ANSWER : barrels.

(5) What is the MAASP at the time the well is shut in?

(6) What is the new MAASP once the kill mud has been circulated around the

well?

(7) What is the initial circulating pressure? ANSWER _ psi

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(8) What is the final circulating pressure, once the kill mud has

reached the bit?

(11) The well is shut in What is the drillpipe pressure drop per 100

strokes as kill mud is being pumped to the bit?

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• Now you should be able to:

fill-up the well control work sheet.

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Network of Excellence in Training

Basic Well Control

End of Lecture

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