Schlumberger

DFS Differential Pressure Firing System

The differential pressure firing system (DFS) activates the differential pressure firing (DPF) head by using the pressure created between the annulus pressure above the packer and the cushion or sump pressure below the packer. The fullbore packer conversion system routes annulus pressure through the packer to the DPF head. An additional firing head can be installed for redundancy.

The DFS is designed to work with a DST string as well as with other completion types. The combination of the DFS and a fullbore redundant firing system can be used for one-trip underbalanced perforating and completion operations.

The pressure-transfer assembly and flow tube route the hydrostatic pressure above the packer through either a PosiTrieve downhole packer with hold-down section or a FlexPac high performance service packer. The pressure is then routed down an integral flow path in the debris sub and spacer pipe to the DPF head. The oil piston automatically closes to prevent formation pressure from entering the annulus after the packer has been set and the guns have been fired. The DPF head detonates the perforating guns when the required pressure differential across the packer is generated. Depending on preference and the other downhole tools used, firing can be accomplished in several ways:

  • immediately on test valve opening as rathole pressure drops to the tubing cushion pressure
  • after test valve opening as cushion backpressure is reduced
  • after test valve opening as pressure increases on the annulus
  • without a test valve by displacing a light fluid cushion; setting the packer; and reducing cushion backpressure, applying pressure to the annulus, or both.

Features

  • Release mechanism shear pin is retained; shears upward (against gravity).
  • Packer must be set and sealed to achieve differential pressure.
  • System allows flexible job design.
  • Completion string does not need to be fullbore.
  • System is not sensitive to debris.
  • System can be used with redundant firing heads.

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DFS Differential Pressure Firing System
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