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  • Name: Drilling-out-free Multiple Stage Cementer
  • ID: 21008
  • Views : 107

1.Purpose
Drilling-out-free multiple stage cementer (which is called stage collar for short) is a special tool used for two-stage cementing operations. With this tool, the interval to be cemented can be cemented in two stages from bottom to top. It can also accomplish the cementing operation for any interval. 
The two-stage cementing operation with drilling-out-free multiple stage cementer can decrease the hydrostatic pressure of annulus fluid column. It reduces the possibility of lost circulation during cementing operations, lowers the operation pressure and shortens the cementing operation time. Meanwhile, it can prevent or reduce the oil/gas/water channeling caused by cement slurry weightlessness, which is in favor of enhancing cement job quality.
Drilling-out-free multiple stage cementer is another major improvement based on MSC mechanical multiple stage cementer. Its structure is scientific, standardized and reasonable. It does not need tripping in for drilling out after cementing, so it saves the drilling out time and drilling cost. 
Structure and Working Principle
The structure and accessories of drilling-out-free multiple stage cementer are shown in Fig.1.
It mainly consists of 5 parts, including stage collar, flexible plug, gravity-type opening plug, closing plug and flexible plug seat (plug bump ring). The upper end and lower end of the collar outer cylinder are processed into box and pin respectively which are used to connect casing. The closing sleeve is fixed to the opening plug seat and closing plug seat by pin forming an integrated structure. There are 4 circulating ports on the upper parts of the closing sleeve and outer cylinder respectively which are blocked by the opening plug seat.  
Fig.1 Drilling-out-free Multiple Stage Cementer and its Accessories
Working process of drilling-out-free multiple stage cementer
Firstly, install the flexible plug seat and stage collar inside a casing coupling of the float collar as per the cementing design, connect it to casing and RIH with the casing string.
After finishing the first stage cementing operation, cement slurry pushes the flexible plug to move downwards, pass the stage collar and then bump on the flexible plug seat. The first stage displacement is then accomplished.
Next, drop in the opening plug. It falls freely to the stage collar. Pressure starts to build up after setting the opening plug in the opening plug seat. Then, the shear pin is sheared to make it move downwards. The circulating ports are exposed to make the casing connected to the annulus. Now it’s ready to conduct the second stage cementing operation.
After the second stage cementing operation, the cement slurry pushes the closing plug to move downwards until setting on the closing plug seat. Increase the pump pressure and shear the pin again, which pushes the closing plug seat to move downwards and brings the entire closing sleeve to move downwards to close the circulating ports. There is a dog to connect the stage collar outer cylinder to the closing sleeve which can prevent the closing sleeve from sliding upwards or downwards, so as to close the two-stage collar permanently. The components including opening plug seat, closing plug seat and closing plug will fall freely together.
Model, Specification and Main Technical Parameters of the Drilling-out-free Multiple Stage Cementer


NO.


Model

YFZ140

YFZ178

YFZ245

1

Specification

Φ139.7 (51/2")

Φ177.8 (7")

Φ244.5 (9 5/8'')

2


Rated load, t

120

170

210

3


Sealing capability, Mpa

25

25

25

4


Opening pressure, Mpa

7

5


Closing shearing pressure, Mpa

5

6


Connection


Long round thread/buttress thread

7


Max. OD of the body, mm

Φ170

Φ208

Φ282

8


Drift diameter of the body, mm

Φ119

Φ156

Φ220

9


Applicable casing wall-thickness, mm

9.17

9.19, 10.36

8.94, 10.03, 11.05

10


Flexible plug length, mm

547

584

654

11


Gravity-type opening plug length, mm

310

380

440

12


Closing plug length, mm

241

250

255

13


Total length, mm

884

926

966

It adopts the advanced internal-closing structure which is reasonable with high sealing capability.
Performance Characteristics
It has permanent closing function, that is, there is a dog to connect the outer surface of the closing sleeve to the inner surface of collar outer cylinder, which is used to lock the closing sleeve and prevent it from sliding upwards or downwards, so as to achieve permanent closing.
During the processes of opening and closing, there is no problem of liquid compressing inside small chamber.
After the displacement bump, the components including opening plug seat, gravity plug, closing plug seat and closing plug will fall freely together. So it does not need another trip-in for drilling out.

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