Volumetric Control Method Principle in Well Control Operations

The Volumetric Control Method is a well control technique employed to manage bottomhole pressure (BHP) while enabling preparations for well circulation or bullheading kill fluid into the wellbore. It is not intended to completely kill the well, but rather to provide a controlled environment until definitive well control measures can be implemented.

The Principle of Controlled Expansion

The core principle of Volumetric Control lies in facilitating the controlled expansion of a gas influx as it migrates up the wellbore. This is achieved by maintaining constant casing pressure while strategically bleeding off mud at the surface. The casing pressure is only held constant during mud bleed-off; otherwise, it is allowed to rise naturally. Each barrel of mud removed from the annulus induces the following effects:

1. Accommodation of Expanding Gas Bubble: The removed volume allows the gas bubble to expand by one barrel within the wellbore.
2. Reduction in Hydrostatic Pressure: The hydrostatic pressure exerted by the mud column in the annulus decreases.
3. Calculated BHP Reduction: The bottomhole pressure experiences a calculated decrease corresponding to the reduction in hydrostatic pressure.

Management of Bottomhole Pressure Using Volumetric Control Method

Volumetric Control operates through a series of steps that create a cyclical pattern of rising and falling BHP. The process follows these steps:

1. Waiting for Gas Bubble Rise: The well is shut-in, allowing the gas bubble to migrate upwards. During this phase, both casing pressure (CP) and BHP increase.
2. Bleed of Mud while Maintaining Constant Casing Pressure : To prevent further casing pressure rise, mud is bled off from the annulus while maintaining a constant casing pressure (CP). This action reduces BHP.
3. Well Shut-In and Pressure Rise: The well is shut-in again, and the cycle restarts. The gas bubble continues to rise to a planned value, leading to a further increase in casing pressure (CP) and BHP.
4. New Casing Pressure Bleed: Once casing pressure (CP) reaches a new, higher level, mud is bled off again to maintain this pressure. This process lowers BHP once more.

By repeating this cycle, BHP is maintained within a controlled range (almost constant). The lower limit ensures sufficient pressure to prevent another influx, while the upper limit safeguards against a formation fracture. The cycle continues until either the casing pressure stabilizes (indicating cessation of gas migration) or the entire gas influx reaches the surface (in scenarios where the gas is distributed throughout the wellbore).

References

Cormack, D. (2007). An introduction to well control calculations for drilling operations. 1st ed. Texas: Springer.

Crumpton, H. (2010). Well Control for Completions and Interventions. 1st ed. Texas: Gulf Publishing.

Grace, R. (2003). Blowout and well control handbook [recurso electrónico]. 1st ed. Paises Bajos: Gulf Professional Pub.

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