In which scenario would the pressure readings from the drill pipe and casing differ?

In the context of well control, understanding the difference in pressure readings between the drill pipe and casing is vital for identifying potential issues. When a blowout occurs, the pressure inside the formation can rapidly exceed the hydrostatic pressure exerted by the column of fluid in the wellbore. This situation typically leads to an influx of formation fluids into the well.

Under these conditions, the pressure reading in the casing may increase significantly due to the influx of high-pressure formation fluids, while the drill pipe may show a relatively lower pressure reading. This discrepancy is crucial as it indicates a dangerous situation where formation fluids are coming into the wellbore, and appropriate well control procedures need to be exercised to prevent catastrophic failure.

In contrast, during a gas migration event, completely shutting in the well, or when resuming drilling operations might not show significant differences in pressure between the drill pipe and casing due to the well’s static or controlled conditions. Therefore, the scenario that distinctly leads to differing pressure readings between the two systems is indeed a blowout, making it a critical consideration in the practice of well control.