With gas kick in the well, the conventional stripping method is not application because it won’t account for the gas migration and expansion; therefore, the special stripping procedure, Stripping with Volumetric Control, will be utilized for this case. This procedure is designed to strip the drill string back into the well with gas influx while the bottom hold pressure is maintained nearly constant.
Figure 1 – Stripping With Volumetric Control
The Stripping with Volumetric Control procedures are as follows;
- Determine whether the drillstring weight is over the pressure force pushing upwards
- Select required Pressure Increment (PI)
- Select Safety Factor (SF)
- Determine Mud Increment (MI)
Mud Increment (MI) is calculated by the following equation
MI = Mud Increment (MI), bbl
PI = Pressure Increment (PI), psi
ACF = annular capacity factor, bbl/ft
MW = mud weight, ppg
- Determine how many feet that you need to strip to penetrate the kick. This calculation must be account for gas migration and stripping speed. You can read more details here –
- Determine pressure increase when the drillstring penetrate the kick. You can read more details about this topic here –Kick Penetration For Stripping Operation
2. Stab a safety valve (full opening safety valve) and close the valve and then follow by an IBOP valve.
Figure 2 – Stab a safety valve and IBOP
3. Ensure no leakage between connections.
4. Adjust the closing pressure to allow the stripping operation.
5. Open Full Opening Safety Valve (FOSV) and strip the drillstring into the well until the casing pressure increase by Safety Factor (SF) + Pressure Increment (PI). No bleeding off during the step#4.
6. Maintain constant casing pressure by bleeding off fluid while stripping until the difference between the drillstring displacement and the actual mud bled back equals to Mud Increment (MI).
7. Strip into the well without bleed off fluid until the casing pressure increases by Pressure Increment (PI).
8. Repeat step#6 and #7 until the drillstring penetrates the gas kick. Once the gas kick is penetrated, you need to allow casing pressure increased by pre-determined figure. This is will be your new casing pressure. Practically, you can add the pressure increase caused by the kick penetration into the safety factor and use the mud increment based on the volume between drillstring and the casing. This will be the conservative way which can prevent you to be in an underbalanced condition.
9. Strip into the desired depth by repeating step#6 and #7.
Reference books: Well Control Books