Primary well control is the most important barrier while drilling and completing any wells so it is imperative to ensure that the primary well control is effectively maintained. When various precautions and procedures have been followed, effective primary well control can be achieved. These procedures can be seen below:
Using a trip sheet (an accurate log), it is possible to maintain tripping both in and out of the well. A trip sheet can help to record the volume of mud that not only enters the well but also that is displaced when tripping. During tripping, the changes in mud volume can be measured using a calibrated trip tank.
For any steel removed, a specific amount of mud is entered into the well when the tripping pipe or drill collars from the hole. To ensure proper well monitoring, tripping may need to be stopped whenever the volume of removed steel significantly outweighs the volume of mud required. After stopping, consideration should also be made towards returning back to bottom in order to condition the mud (and find the cause of the issue). At all times, the drill floor should have the required crossover subs and a full opening safety valve readily available.
Mud Weight (Mud Density)
To control the well, the correct weight needs to be maintained and this can only occur when mud entering/leaving the well is weighed. The shaker man is normally in charge of this process every 15 – 30 minutes or so; however, this’ll completely depend on company policy and the drilling operation in question.
To ensure well stability, flow checks can be carried out regularly. To remove ECD effects, the well should be checked with the pumps off. Usually, when a trip takes place in certain locations, flow checks will be performed. These locations include the bottom, the casing shoe, and before the BHA is pulled into the BOPs.
To compensate for the ECD loss, the Trip Margin is an overbalance; during a trip out of the hole, this will also help to overcome swab pressure effects.
If available, another important process for well control is mud logging. With a mud logging unit, there will be opportunities for gas analysis, pore pressure trends, gas detection, recording flow line temperatures, cuttings density, recording penetration rates, and recording mud densities (both in and out).
Short Trips/Wiper Trips
Before pulling out of the hole a short trip, some circumstances will require a consideration of either five or ten stands. From here, the well will circulate as expected and the mud can be carefully monitored.
Pumping a Slug of Heavy Mud
Often, this process can be used so the pipe can be pulled dry (and to monitor the hole accurately during the trip). After pumping slug, a driller must wait until slug stop falling down by monitoring a well via a trip tank. The flow return should be completely stopped prior to continuing pulling out of hole. Otherwise, a record in a trip sheet may be off and it can cause confusion while monitoring a well.
The flow line recorder and pit level recorder need to be set at appropriate values and checked regularly; this includes both the high and low settings.
Despite all the processes listed above, good communication will still be important. The logging unit and driller must always be informed when mud is transferred to the active system.