Wait and Weight Method:

The ‘Wait and Weight method’, also known as ‘Engineer’s method’ is aimed at controlling a well with one circulation. It involves displacing the kill-weight mud into the drill string to remove the wellbore influx. This method requires meticulous calculations and pressure monitoring to achieve safe and effective well control.

The process involves several essential steps:

1. Well Shut-in: The well is shut in to stop the flow of formation fluid into the well as soon as a kick is detected. Soft Shut-in or Hard Shut-in methods can be adopted depending on the company policies.

2. Pressure Stabilization and Data Recording: The Shut-in Drill Pipe (SIDP) pressure, ‘Shut-In Casing Pressure (SICP), and pit gain are recorded after allowing some time for them to stabilize.

3. Well Control Calculations: Based on stabilized pressures and well configuration details, various crucial calculations are made including the bottom hole pressure, MAASP, kill mud weight requirement to balance the formation pressure, pump strokes requirement etc. A drill pipe pressure schedule is prepared ensuring that the bottom hole pressure is kept above the formation pressure through the well-killing process.

4. Mud Weight Adjustment: The mud weight in the system is increased to the necessary kill mud weight based on the calculations.

5. Pump start-up to circulate kill mud: Pump is started gradually in steps of 5 strokes per minute to reach the required kill rate. Casing pressure is kept constant during this circulation start-up process by manipulating the choke valve to ensure that the bottom hole pressure remains constant during this step.

6. Pumping kill mud: Kill-weight mud is pumped through the drill pipe at the kill rate. The drill pipe pressure schedule is followed until the kill weight mud reaches the bit by manipulating the choke valve.

7. Constant Drill Pipe Pressure: Once the kill weight mud reaches the bit, the drill pipe pressure is maintained constant for the rest of the cycle. Maintaining the planned pressure schedule ensures that the bottom hole pressure remains equal to or slightly greater than the formation pressure, thus avoiding a secondary kick situation.

8. Gas Expansion: A controlled gas expansion occurs in the annulus in the case of a gas kick. Casing pressure and pit volume increase should be expected due to gas expansion. It is important to hold the drill pipe pressure and pump rate at the predetermined level to maintain the bottom hole pressure above the formation pressure.

9. Mud weight verification: After completing the circulation cycle, verify that the outcoming mud weight is the same as the kill mud weight.

10. Shutdown and Flow Check: Once the circulation is completed, pumps are shut down to flow check and confirm that the well is stable.

11. Mud Conditioning: If necessary, mud circulation and conditioning are carried out until satisfactory mud properties are attained.