Introduction

I. Introduction

Retrievable bridge plug is a down-hole plugging tool used in oilfield with hydraulic setting, stepped locking, bi-directional slips and special tools for unlocking, it featuring as follows:

1. Going down into the hole easily: special design of hydraulic slip, which would not hamper the setting process when blocked in the down-hole, used in inclined and horizontal wells.
2. Setting stably: special design of packing element structure, greatly improving the pressure tolerance of the bridge plug.
3. Releasing off easily: every batch of products being strictly tested before delivery, with the rating releasing pressure.
4. Bi-directional slips for firmly anchoring.
5. Fishing out easily: special design of fishing mechanism, forcing the slips to reset, success rate of fishing out 100%.
6. Being able to wash the well: the flushing passage for direct and inverse well-flushing when the tool going down the preset position.

II. Technical parameter

III. Structure and working principle

The retrievable bridge plug is composed primarily of the setting mechanism, sealing mechanism, unsetting mechanism and so forth; used with a unique automatic locking mechanism firmly withstanding bi-directional pressure.

Working principle:

1. Setting and releasing: lower the bridge plug to the designed depth, locating the steel ball onto the surface of the ball seat and sealing the passage under the ball seat, then pressurize the tubing to about 8-10 MPa, cutting the setting shear pin and continuing pressurizing to force the piston sleeve downward against the setting piston, the fixing shear pin being cut and the setting piston moving downward with the element mandrel and the upper cones under pressure, thus sitting the slip anchor on the inside wall; continuing pressurizing, the element beginning to expand, when the pressure being about 20-22 MPa, the releasing shear pin being cut and the setting then being completed, with releasing achieved simultaneously. At the same time, the upper joint, outer element, connecting sleeve, ball seat, piston sleeve and so forth has not any rigid connection with the bridge plug body, so the upper portion can be easily pulled out, the locking ring being engaged with the buttress thread on the element mandrel, thus maintaining the element in the setting state.
2. Unsetting: tubing goes down the special unsetting tool, seizing the bridge plug fishing head and picking up the tubing string, then cutting the unsetting shear pin and continuing picking up, the spring case being moved upward by the mandrel, separating the spring case from the blank mandrel, then continuing picking up, removing the automatic locking mechanism of the bridge plug, the element retracted and the slips retracted into the slip socket, thus unsetting the bridge plug, whose assembly being pulled out onto the surface with the tubing.
3. Security measures: use a releasing fishing tool, rotating the tubing string to the right and retrieving the fishing tool when catching failure leads the bridge plug to be hardly retrieved. If the tool blocked in the casing and needing drilling and milling, a flat rolling-ball type milling shoe with surfacing YD alloy is recommended.

Matters should be noticed:

1. Keep the components and parts clean before installation so as not to hamper the assembling, buttering the O-ring and threads; assuring the direction of the sawtooth buckle, being rotating-proof without a deformation.
2. Ensure that the down hole is unobstructed before the bridge plug going down the hole, best to have a pigging and flushing before the bridge plug going down in an unclear situation.
3. The going down speed of the bridge plug should be about 0.5m/s, the slips and element being away from the casing coupling.
4. If the bridge plug gets stuck in a soft blockage or the liquid in the tubing hampers the falling of the steel ball, a direct and inverse flushing can be operated, but the pressure of the direct flushing should be controlled in 5MPa.
5. When blocked during running in the fishing tool, a continuous sand flushing should be operated with running in the tubing string simultaneously until the fishing accomplishing.
6. A ventilated dry storage is not necessary, conventional oil sealing.