Well control with one-circulation method
The one-circulation method is a well-control procedure. To implement this method certain guidelines must be followed to ensure a safe kick-killing exercise. Although the procedure is relatively simple, its mastery demands basic knowledge of the practical steps taken during the process. Checkpoints indicate potential problems.
A kill sheet is normally used during conventional operations. It contains prerecorded data, formulas for the various calculations, and a graph—or other means—for determining the required pressures on the drillpipe as the kill mud is pumped. Although many operators have complex kill sheets, only the basic required kick-killing data is necessary. A kill sheet is shown in the example problem in the following section.
A summary of the steps involved in proper kick killing follows. The sections not directly applicable to deepwater situations are noted. When a kick occurs, shut in the well using the appropriate shut-in procedures. Once the pressures have stabilized, follow these steps to kill the kick:
1. Read and record the shut-in drillpipe pressure, the shut-in casing pressure, and the pit gain. If a float valve is in the drillpipe, use the established procedures to obtain the shut-in drillpipe pressure.
2. Check the drillpipe for trapped pressure.
3. Calculate the exact mud weight necessary to kill the well and prepare a kill sheet.
4. Mix the kill mud in the suction pit. It is not necessary to weight up the complete surface-mud volume, initially. First pump some mud into the reserve pits.
5. Initiate circulation after the kill mud has been mixed, by adjusting the choke to hold the casing pressure at the shut-in value, while the driller starts the mud pumps. (Not applicable in deep water.)
6. Use the choke to adjust the pumping pressure according to the kill sheet while the driller displaces the drillpipe with the exact kill-mud weight at a constant pump rate (kill rate).
7. Consider shutting down the pumps and closing the choke to record pressures when the drillpipe has been displaced with kill mud. (Note: If the kill mud is highly weighted up, settling and plugging may occur.) The drillpipe pressure should be zero, and the casing should have pressure remaining. If the pressure on the drillpipe is not zero, execute the following steps:
- Check for trapped pressure using the established procedures. If the drillpipe pressure is still not zero, pump an additional 10 to 20 bbl (1.5 to 3 m3) to ensure that kill mud has reached the bit. The pump efficiency may be reduced at the low circulation rate.
- If pressure remains on the drillpipe, recalculate the kill mud weight, prepare a new kill sheet, and return to the first steps of this procedure.
8. Maintain the drillpipe pumping pressure and pumping rate constant to displace the annulus with the kill mud by using the choke to adjust the pressures, as necessary.
9. Shut down the pumps and close the choke after the kill mud has reached the flow line. The well should be dead. If pressure remains on the casing, continue circulation until the annulus is dead.
10. Open the annular preventers, circulate and condition the mud, and add a trip margin when the pressures on the drillpipe and casing are zero. In subsea applications, the trapped gas under the annular is circulated out by pumping down the kill line and up the choke line with the ram preventer below the annular closed. The riser must then be circulated with kill mud by reverse circulation, down the choke line and up the riser, before the preventers can be opened.
Well-control learning experiences are often best accomplished by observing an actual kick problem. The example below has been provided for this purpose.
Example of a kick problem
While drilling the R.B. Texas No. 1 in the Louisiana Gulf Coast offshore area, a company representative carried out his normal drilling responsibilities related to well control in the event that a kick should occur. Some items that the representative did are listed below:
- Read the appropriate MMS orders and complied with the provisions.
- Checked the barite supplies to ensure that a sufficient amount of barite was on board to kill a 1.0-lbm/gal kick, if necessary.
- Recorded on the driller’
s book that the kill rate was 21 spm and 800-psi pump pressure.
- Calculated the drillstring volume as follows:
4½-in. drillpipe to 14,000 ft.
6½×2-in. drill collars to 15,000 ft.
4½-in., 16.6-lbf pipe capacity
= 0.01422 bbl/ft×14,000 ft =199 bbl
6½×2-in. collar capacity
=0.0039 bbl/ft×1,000 ft = 3.9 bbl
Total = 199 + 3.9 = 202.9 bbl
Shut-in and weight-up procedures
The drillers on the rig had just changed tours when a drilling break was observed. The well was checked for flow. A flow was recorded with the pumps off, and the following steps were taken:
1. The kelly was raised until a tool joint cleared the floor. (A jackup rig was in use.)
2. The pumps were shut down.
3. The annular preventer was closed.
4. The company representative was notified that the well was shut in.
5. The driller told his crew in the mudroom to stand by in case the mud weight had to be increased. Then, the company representative went to the floor and read the pressures as follows:
psidp = 240 psi
psic = 375 psi
Pit gain = 31 bbl
After checking for trapped pressures, he recorded the information on his kill sheet. From the kill sheet, he calculated that he needed to raise the mud weight from the 13.1-lbm/gal original weight to 13.4 lbm/gal. He was walking to the mudroom, to tell the derrickman that he needed 13.4-lbm/gal kill mud, when he noticed the pits were almost full. He knew the needed barite would raise the mud level, so he instructed the derrickman to pump off a foot of mud, section off the suction pit, and increase the weight to 13.4 lbm/gal. The representative judged that it would be better to pump off the mud at that time, rather than after the killing operation was started.
The pump output was read from the mud engineer ’ s report as 5.2 strokes/bbl for the 6×18-in. duplex mud pump. The volumetric output at 21 spm was 0.1916 stroke/bbl×21 spm = 4.0 bbl/min. The representative knew he could cripple his pumps according to the chart previously provided to him but felt that 4.0 bbl/min was not much more than the recommended 1 to 3 bbl/min as a kill rate.
Kill sheet preparation
The representative prepared his kill sheet as shown in Fig. 1.
Working the pipe
While the mud weight was increased and the kill sheet was being prepared, the driller was instructed to work the pipe every 10 minutes by moving it up and down. He was also instructed not to move a tool joint through the annular preventer.
Displacing the drillpipe
After the mud was weighted to 13.4 lbm/gal, the representative was ready to displace the drillpipe. He instructed the driller to start his pumps and run them at 21 spm. Then, he cracked open the choke slightly and held his casing pressure at 375 psi until the driller had the pumps at the kill rate. The choke was used to control the drillpipe pressure to decrease it gradually according to values on his kill sheet. The pressures were maintained as shown in Table 1.
When the drillpipe had been displaced, the pump was shut down and the choke was closed. The pressures were then as follows:
psidp = 0 psi psic= 350 psi
The pressure on the drillpipe told the representative that the heavier kill-mud weight was sufficient to kill the well. If it had not been of sufficient density, some pressure would have remained on the drillpipe.
Displacing the annulus
The representative was now ready to displace the annulus with kill mud. He initiated pumping by adjusting his choke to maintain 350 psi on the casing while the driller started the pumps. After the pumps were running at 21 spm, he used the choke to maintain the drillpipe pressure constant at the final circulating pressure of 820 psi. He held this pressure until a 13.4-lbm/gal mud weight was observed at the shaker, at which time he closed in the well. The drillpipe and casing had zero pressure. The choke and the annular preventer were opened. The well was dead.
There are several items that the representative considered after the well was dead to ensure that the procedure was complete. He circulated and conditioned the mud in the hole and added a trip margin to the mud weight so that he could make a short trip. Additional barite was ordered from the mud company to resupply the bulk tank. He also took time to inspect his equipment to identify any damage sustained from the kick.
|psic||= shut-in casing pressure, psi|
|psidp||= shut-in drillpipe pressure, psi|
Noteworthy papers in OnePetro
Kai Fan, Ferda Akgun, Abukari Iddris 2011. A Different Approach in Handling Well Control Kick Circulation Which May Have Significant Advantages Over Existing Method, SPE/IADC Middle East Drilling Technology Conference and Exhibition, 24-26 October 2011, Muscat, Oman, 148514-MS, http://dx.doi.org/10.2118/148514-MS
J.R. Smith, and B.M. Patel 2012. A Proposed Method for Planning the Best Initial Response to Kicks Taken During Managed-Pressure-Drilling Operations, Volume 27, Number 2, 143101-PA, http://dx.doi.org/10.2118/143101-PA