To ensure primary well control is in place the following procedures and precautions must be observed.
Mud WeightMud into and out of the well must be weighted to ensure the correct weight is being maintained to control the well.
This task is normally carried out by the shaker man at least every thirty minutes or less, depending upon the nature of the drilling operation and/or company policy.
Tripping ProceduresTripping in or out of the well must be maintained using an accurate log called a trip sheet. A trip sheet is used to record the volume of mud put into the well or displaced from the well when tripping.
A calibrated trip tank is normally used for the accurate measurement of mud volumes and changes to mud volumes while tripping.
When tripping pipe or drill collars out of the hole, a given volume of mud is put into the well for the volume of steel removed. If the volume required to fill the hole is significantly less than the volume of steel removed, then tripping must be stopped to ensure the well is stable, and consideration given to going back to bottom to condition the mud and investigate the cause of the problem.
THE HOLE MUST BE KEPT FULL AT ALL TIMES
A full opening or safety valve should be available at all times on the drill floor together with the required crossover subs. A non-return (i.e. grey) valve should also be readily available.
Trip Margin (Safety Factor)
Trip Margin (Safety Factor) is an overbalance to compensate for the loss of ECD and to overcome the effects of swab pressures during a trip out of the hole.
Flow checks are performed to ensure that the well is stable. Flow checks should be carried out with the pumps off to check the well with ECD effects removed. Flow checks are usually performed when a trip is going to take place at the following minimum places:
- on bottom
- at the casing shoe
- before the BHA is pulled into the BOP's
Short Trips/Wiper Trips
In some circumstances prior to pulling out of the hole a short trip, 5 or 10 stands should be considered. The well is then circulated and mud returns carefully monitored.
Pumping a Slug of Heavy Mud
This is a practice often carried out to enable the pipe to be pulled dry and the hole to be more accurately monitored during the trip. The following equation is used to calculate the dry pipe volume for the slug pumped:
Dry Pipe Volume = Slug Volume x (Slug Weight / Mud Weight - 1)
This dry pipe volume can be converted to Dry Pipe Length by dividing this volume by the internal capacity of the pipe as illustrated in the following equation:
Dry Pipe Length = Dry Pipe Volume (bbls) / Drill Pipe Capacity (bbls/ft)
A logging unit if available is extremely important particularly with respect to well control. The unit carries out some of the following services:
- Gas detection in the mud
- Gas analysis
- Cuttings density analysis
- Recording mud densities in and out
- Recording flow line temperatures
- Recording penetration rates
- Pore Pressure Trends
If a transfer of mud to the active system is requested the driller will be informed, the logging unit must likewise be informed. Good communication all round is essential.
The high and low settings for the pit level recorder and flow line recorder must be checked and are set to appropriate values.