Managing Well Control During Trips: A Simple Action Plan

Well control is vital in oil and gas drilling operations, especially when something unexpected happens. One common issue is when the well doesn’t take the right amount of fluid during a trip or begins to flow when the bit is off-bottom. These signs often mean that formation fluids (such as gas or oil) have entered the well, which could lead to a dangerous blowout if not handled quickly. This guide explains what steps a driller should take to control the well and prevent escalation, along with tips to avoid similar problems in the future.

Immediate Actions When Hole Fill is Incorrect or Flow Occurs with the Bit Off Bottom

When a driller notices that the well isn’t taking the correct amount of fluid or that the well starts to flow with the bit off bottom, immediate action is necessary. These steps are crucial to prevent the situation from worsening.

1. Stop Hoisting Immediately
   The first thing to do is stop lifting the drill string. If the string is raised, more formation fluid could enter the well, making the situation worse. Stopping hoisting helps slow down or stop the further influx of fluids.

2. Perform a Flow Check
   After stopping hoisting, the next step is to check for flow in the well. This helps determine if the well has become underbalanced (when the pressure inside the well is less than the pressure of the surrounding formation). The driller checks for fluid flow through the flowline or choke.

   • If there’s no flow: The driller should return the bit to the bottom and start circulating the influx through the choke, effectively removing the unwanted fluid and regaining control.
   • If there’s flow: This means the well is flowing, and immediate well control measures must be taken.

3. Shut the Well In
   If the well is flowing, the driller must quickly shut the well in to stop the flow. The driller should also inform the supervisor to keep everyone on the team aware and ready for further actions.

   • Shut the Blowout Preventer (BOP): The driller should close the BOP as soon as possible to stop any further flow. The BOP, along with choke and kill systems, should be ready to use immediately.

   • Strip Back to Bottom: If possible, the driller can lower the drill string back to the bottom of the well. Stripping means using the weight of the drill string to enter the well against a closed BOP (usually a annular BOP), while the pressure is controlled through the choke. This allows the influx expand in a controlled manner to minimize the wellbore pressure.

   • Use the Choke: Once the string is back at the bottom and circulation is underway, the driller can use the choke to control the flow of fluids. The choke is essential for regulating the pressure and ensuring that the influx is safely removed from the wellbore.

What to Do If Stripping Isn’t Possible

In some cases, stripping might not be an option due to equipment limitations or other operational factors. If this happens, the driller can try these alternative methods to control the influx:

1. Snubbing
   If stripping is not possible because the well pressure is too great, snubbing may need to be used. However, snubbing involves using very specialized equipment to push the drill string back into the well under wellbore pressure when the weight of the drill string is insufficient by itself. This method helps continue circulation and manage the influx, but it requires more equipment and expertise.

2. Volumetric Method
   If neither stripping nor snubbing are immediate option, or the rig is unable to circulate, the driller can use the volumetric method to control the wellbore pressures. This technique involves managing the influx volume as it migrates upwards, thus preventing excessive pressures on the formations and surface equipment. It allows the influx to be gradually evacuated, while controlling pressure and avoiding a underground blowout or surface equipment failure.

After Evacuating the Influx: Restoring Control

Once the influx has been safely removed, it’s important to confirm that the well is under control. At this point, the driller can resume normal operations, but some additional steps should be taken to avoid future issues.

1. Consider Increasing the Trip Margin
   After stabilizing the well, the driller should consider increasing the “trip margin.” The trip margin is the difference between the pressure in the well and the pressure in the formation. A larger trip margin helps prevent future influxes by making the well more stable during trips.

   • If formation pressures have changed or the previous influx suggests a higher risk of kicks, increasing the trip margin is a good idea.
   • The driller should work with mud engineers to check the well’s pressure and adjust the mud weight if necessary.

2. Reduce the Speed of Pulling the Pipe
   Swabbing (a sudden pressure change when pulling the pipe) can happen if the pipe is pulled too quickly. If the trip margin cannot be increased or the mud viscosity reduced, the driller may need to slow down the pipe-pulling speed.

Conclusion

Handling well control issues, such as when the well doesn’t take enough fluid or begins to flow with the bit off bottom, requires quick and careful action. The driller should stop hoisting, perform a flow check. If the well is flowing, the driller should secure the well, strip back to bottom, and circulate the influx out using the choke. If stripping is not possible, alternative methods like snubbing or the volumetric method can be used. After re-establishing well control, the driller should consider increasing the trip margin and/or adjusting the speed of pulling the pipe to avoid future influxes.

By following these steps and communicating clearly with the team, the driller can effectively manage well control situations and prevent dangerous outcomes. Maintaining control of the well is essential to ensure the safety of personnel and the success of the drilling operation.

For more detailed information on how to react to a well control issue while tripping and the associated well control methods, please refer to my Well Control Manual V2.6 at: https://learn-well-control.com/product/well-control-manual-by-edwin-ritchie/