Prior to implementing the Wait & Weight Method, the relevant sections of the Kick Sheet as covered in Paragraph 3 should be completed.
The Driller’s method is a two complete circulation method. The kick is circulated out of the hole by the first circulation with the original mud. The second circulation is carried out with the weighted mud to kill the well.
Prior to the first circulation, the following calculations are necessary: (a) Determine the circulation rate
The circulation rate for the first circulation of the Driller’s Method is not limited by the baryte mixing capacity of the rig. Limiting factors will include the additional wellbore pressures due to circulation, and further practicalities as outlined in Chapter 1. Record the chosen circulating rate SCR and the corresponding pumping data in the kick sheet. (b) Calculate the initial circulating pressure
The initial circulating pressure at the start of the first circulation is calculated in the same manner as the Wait and Weight Method, although the drillstring displacement volume/time is not significant in this case.
The initial circulating pressure will be maintained constant throughout the first circulation since the mud weight is not changed.
(c) Determine the displacement times and corresponding pump strokes These figures are calculated in exactly the same manner as the Wait and Weight Method. (d) Plot the standpipe pressure schedule
The standpipe pressure is held constant throughout the first complete circulation at the initial circulating pressure.
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The following steps can be used as a guide for the procedure for the displacement of the␣kick:
1 Bring the pump up to speed for the first complete circulation
• Line up the pump to the drillpipe and route returns through the choke manifold to the mud gas separator.
• Set the stroke counter on the remote choke panel to zero.
• Open the remote operated choke at the same time as the pump is slowly brought up to speed. Consider stroking the drillstring up at this point.
• Maintain the choke pressure equal to the original shut-in casing pressure as the pump is slowly brought up to speed. This may take 1/2 to 1 minute.
• Once the pump is up to speed record the initial circulating pressure. If the actual initial circulating pressure is considerably different from the calculated value, stop the pump, shut-in the well and investigate the cause.
If the actual initial circulating pressure is equal to, or reasonably close to the calculated value, continue the displacement, holding the standpipe pressure at the value recorded when the pump was first brought up to speed.
Any marginal difference between the actual and calculated initial circulating pressure is most likely to be due to the fact that the SCR pressure used to calculate the initial circulating pressure was inaccurate. The actual SCR pressure can be determined from the initial circulating pressure as follows:
Pscr =Pic −Pdp
This adjusted value for the SCR pressure should be used for estimating the circulating pressures for the second complete circulation.
2 Circulate the influx from the well maintaining constant bottom hole
pressure
Influx behaviour during circulation will be similar to the Wait and Weight Method requiring similar choke manipulation.
Choke pressures will inevitably be higher than if the Wait and Weight Method had been␣used. These higher pressures will be reflected downhole, causing greater stress in the openhole.
Once the influx has been displaced from the hole, the shut-in drillpipe and shut-in casing pressure should be equal. If the casing pressure is higher than the drillpipe pressure, this is evidence that there is still some kick fluid in the annulus, or the mud weights are out of balance.
Prior to circulating kill weight mud into the hole, the calculations as outlined in Paragraph␣3 “Kick Sheet” should be carried out. The following further calculations are then worked:
(a) Determine the circulation rate for the second circulation
The circulation rate is determined on the same basis as if the Wait and Weight Method had been used.
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(b) Calculate the initial circulating pressure
The initial circulating pressure will be the same as for the first circulation. The initial circulating pressure is therefore calculated as follows:
Pic = Pdp + Pscr
where Pic = Second circulation initial circulating pressure (psi)
Pdp = Drillpipe pressure recorded prior to second circulation (psi) Pscr = Slow circulating rate pressure (psi)
(c) Calculate the final circulating pressure
As with the Wait and Weight Method, the circulating pressure must be adjusted to compensate for the kill weight mud.
MW2 Pfc = Pscr (at MW1) x
MW1
where Pfc = Second circulation final circulating pressure (psi) MW1 = Original mud weight (SG)
MW2 = Kill mud weight used for second circulation (SG)
(d) Determine the displacement times and corresponding cumulative pump strokes
These figures will be the same as for the first circulation. (e) Plot the standpipe pressure schedule
The standpipe pressure schedule for the second circulation is drawn up in the same manner as for the Wait and Weight Method (Figure 6.1b).
The following can be used as a guide for the procedure of circulating the hole to kill weight mud:
1 Bring the pump up to speed for the second complete circulation
• Change pump suctions without stopping the mud pump, and begin pumping the kill weight mud. (An alternative is to stop pumping and then restart using the procedure for the Wait and Weight Method.)
• Zero the stroke counter on the choke panel.
• Once the pump has been switched to the kill mud, record the initial circulating pressure.
The initial circulating pressure should be the same with the standpipe pressure during the first complete circulation. If this is the case, continue the displacement and adjust the standpipe pressure schedule accordingly.
If the initial circulating pressure has changed considerably, stop the pump, shut in the well, and investigate the cause.
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2 Circulate the hole to kill weight mud maintaining constant bottom hole
pressure
As the drillpipe is displaced with kill weight mud, the standpipe circulating pressure should be stepped down according to the standpipe pressure schedule.
Once the drillpipe has been displaced to kill weight mud, the final drillpipe circulating pressure is held constant by manipulating the choke.
As kill weight mud is circulated up the annulus, the drillpipe pressure will tend to increase. The choke should be adjusted to ensure that the drillpipe pressure is maintained at the final circulating pressure; thereby ensuring constant bottom hole pressure. When the returned mud is at kill weight, the pump should be stopped and the well shut-in. The well should be checked for pressure.
Once the well has been killed, a flowcheck on the choke line return should be carried out before the rams are opened. If this flowcheck indicates no flow, the rams should be opened and a further flowcheck on the annulus carried out.
In line with Company policy, a further complete hole circulation should be carried out␣prior to continuing operations. A suitable overbalance can be added to the mud at this stage.