well_control_methods

7/30/2019 well_control_methods

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Well Control Methods

n Driller’s Method.

n Wait and Weight Method.

n Volumetric Methods.n Lubricate and Bleed Method.



Well Control Methods

At the end of this section you should be able to:

n Describe the different well control methods and its

applications.

n Describe the importance of bottom hole pressure constant

while controlling a well.



Well Control MethodsWell Control Methods

Once the well has been shut in and pressures have been observed to stabilize, threeconventional well control methods are available to circulate out a kick and restore wellcontrol:

n The Driller's.

n The Wait and Weight.

n The Volumetric followed by the Lubricate and Bleed (required in special situations).

All these methods are intended to keep the bottom hole pressure slightly higher thanthe formation pressure, by the adequate use of the surface choke to impose additionalback pressure on the wellbore.

The drillstring on or near bottom is the most desirable position for well control operationsbecause the well can then be most effectively killed using either the Driller’s or the Waitand Weight methods. Therefore, when the drill string is partially (i.e. the bit is off bottomany significant distance) or completely out of the hole and a kick is experienced, everyeffort should be made to safely return the drill string to bottom or as close to bottom aspossible while at the same time maintaining well control.



Driller’s MethodDriller’s Method

The Driller’s method involves two full circulations to kill the well.

n During the first circulation, the drill pipe pressure is maintained at aconstant value until the influx is circulated from the wellbore using

original mud weight.n During the second circulation, kill mud is pumped to the bit while

following the drill pipe pressure schedule established in the kill sheet.If all the kick fluid was successfully circulated from the well in the firstcirculation, the casing pressure should remain constant until the killmud reaches the bit. When the kill mud enters the annulus, the drill

pipe circulating pressure is maintained constant until the kill mudreaches surface.




First circulation: circulate gas out of the hole, holding bottom hole pressure constantusing Original Mud Weight (OMW).

1. Bring the pump to kill rate speed, holding the casing pressure constant at SICP (shutin casing pressure) value.

2. Kill rate speed established, hold drill pipe gauge pressure constant until the influx is

removed from the wellbore.3. Turn the pump off maintaining the casing pressure constant.

4. At this stage the well is not killed, and the SIDPP (shut in drill pipe pressure) andSICP should be the same and equal to the original SIDPP if the influx has been fullycirculated out of the annulus.

5. During the first circulation, mud is weighted up from the OMW to the Kill Mud Weight

(KMW):

KMW (ppg) = SIDPP (psi) ÷ 0.052 ÷ TVD (ft) + OMW (ppg)




n Initial circ. pressure: ICP = SCRP + SIDPP

n Final circ. pressure:

FCP = SCRP x (KMW ÷ OMW)

n Surface–to–bit strokes:Strokes = drill string volume ÷ pump output

n Time to pump surface – bit: Time =

total strokes ÷ Strokes per minute

n Pressure drop per increment =

(ICP – FCP) ÷ Nsteps

Example of Driller’s method – Second Circ. Plot

Nsteps = number of steps selected to bring the drill pipe pressure from ICP to FCP.

Second circulation: circulate kill mud in the hole holding bottom hole pressure constant.1. Prepare a pumping schedule as a function of slow circulating rate pressure (SCRP):




Continue Second circulation:2. Open the choke manifold valve upstream of the choke.

3. Bring the pump to kill rate while holding casing pressure constant.

4. Record the actual circulating drill pipe pressure. If equal to calculated ICP, continuepumping and adjust the stand pipe pressure according to the pumping schedule.

5. If the actual circulating drill pipe pressure is significantly different from the calculatedICP, shut the well in and investigate the reason.

6. Once the kill mud enters the annulus, hold drill pipe pressure constant until the killmud returns to surface.

7. Once kill circulation is complete, the well will be shut in to observe the DP andcasing pressures.

8. If no pressure is measured, the well will be flow checked through the choke beforeopening the BOPs.

(Note: To help in identifying the cause of potential problems, it is important to maintain a good systematic

record of time, pressures, volumes, etc.)



Wait and Weight MethodWait and Weight Method

The Wait and Weight method involves one circulation to kill the well. Once an influx isidentified, the well is shut in, the entire surface system is weighted up to the required kill

weight mud. Kill weight mud is then pumped from surface to bit while following a

pumping schedule. Once the kill mud enters the annulus, a constant drill pipe pressure

is maintained until the kill mud returns to surface.

The procedure for the Wait and Weight method is as follows:

n Prepare kill mud.

n Bring the pumps to kill rate pumping kill mud while holding the casing pressure

constant (less choke line friction for floating units).

n

When the kill rate is established, switch to the drill pipe gauge and follow thepumping schedule until kill mud reaches the bit. At this point hold the drill pipe

pressure constant until the kill mud reaches surface.



Volumetric MethodVolumetric Method

If a gas kick cannot be circulated from the wellbore, the gas bubble will migrateup the hole without expansion (well shut in), thereby causing an increase of allpressures in the wellbore. This may result in excessive surface, casing shoe andbottom hole pressures, increasing the risk of an underground blowout.

To avoid this, it is necessary to allow the influx to expand with time in a

controlled fashion in order to reduce the pressures in the wellbore.

With the volumetric method, the bottom hole pressure is maintained slightly inexcess of the formation pressure following predetermined steps while the gas isallowed to expand as it migrates to surface.

The volumetric method only brings the gas to surface. To remove this gas, theLubricate and bleed method must be implemented.



Lubricate and Bleed MethodLubricate and Bleed Method

With gas at surface after the use of the volumetric method, mud needs to belubricated in the annulus as follows:

n Allow time for the mud to fall through the gas by gravity. The casing pressure

may increase slightly due to the gas being compressed by the mud being

pumped in.n Reduce casing pressure by 100 psi (as an example), by bleeding gas from

the annulus. If mud starts coming back, shut the choke and wait for the gas

to work up to the surface before continuing to bleed. If mud has been bled off

together with the gas, this volume of mud must be additionally re-lubricated

together with the selected volume of mud per each lubrication.n Repeat until all the gas has been bled off from the wellbore.

well_control_methods

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