Under what casing pressure condition is underbalanced perforating performed?

• A. Casing pressure greater than reservoir pressure
• B. Casing pressure equal to reservoir pressure
• C. No casing pressure difference
• D. Casing pressure less than reservoir pressure

Answer: (D)

Underbalanced perforating is done when the casing pressure is lower than the reservoir (formation) pressure. With the wellbore pressure below the formation pressure, fluids from the rock are driven into the wellbore during perforation, helping to minimize formation damage and maximize initial production. If casing pressure were greater than reservoir pressure, or if the pressures were equal, there wouldn’t be the same controlled influx of fluids into the well, which is neither desirable for underbalanced perforating nor provides the same production benefits.