Plug Cementing | What is Plug Cementing?

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Plug Cementing, What is a plug cementing, Remedial cementing, plug cementing, plug cementing process, bump plug cementing

Assignment Plug Cementing

Given the conditions of the Assignment well shown here, determine:

A. The depth to the top of the planned cement plug

B. The volume of post-flush needed behind the cement slurry in order to maintain a balanced pressure condition between the tubing and the tubing/casing annulus

C. The volume of mud needed following the post-flush to displace the slurry to the calculated top of the cement plug

The formula for determining the height of a balanced cement plug is:

$H = \dfrac{V_{Cmt}}{C_{Annulus}\ +\ C_{Pipe}}$

Where:

H = height of cement plug, ft

C_Annulus = Capacity of tubing/hole, tubing/casing, drill pipe/hole or drill pipe/casing annulus, ft³ per linear ft

C_Pipe = Capacity of tubing or drill pipe, ft³ per linear ft

Volume of cement used for plug: 100 ft³

Casing:

$7\ inch,\ 23\ \frac{lb}{ft} (Capacity\ =\ 0.2210\ \frac{ft^3}{ft}$ , or $0.0393\ \frac{bbl}{ft})$

Tubing:

$2.875\ inch,\ 6.4\ \frac{lb}{ft}\ (Capacity\ =\ 0.0325 \frac{ft^3}{ft}$ , or $0.00579\ \frac{bbl}{ft} )$

Annular capacity:

$0.1760\ \frac{ft^3}{ft}$ , or $0.0313\ \frac{bbl}{ft}$

Bottom of plug: 2500 ft

Solution

A. Depth to top of cement plug:

$H = \dfrac{V_{Cmt}}{C_{Annulus}\ +\ C_{Pipe}} =\ \dfrac{100}{0.1760\ +\ 0.0325}\ =\ 480\ ft$

Depth to top of cement plug $= 2500\, ft - 480\, ft\ =\ \textbf{2020 ft}$

B. Volume of post-flush needed in tubing in order to balance plug:

10 bbl of pre-flush in annulus $\Rightarrow \dfrac{10}{0.0313}\ =\ 319\ ft\ \Rightarrow \ 319\ ft\ \quad$

also required in tubing

$319\ ft\ \times 0.00579\ \frac{bbl}{ft}\ =\ \textbf{1.85 bbl post-flush}$

C. Volume of mud needed to displace cement to top of plug depth:

Top of cement = 2020 ft

1.85 bb of post-flush in annulus ⇒ = 319 ft

Displace of mud to (2020 + 319) = 2339 ft

Bbl of mud to displace $=\ 2339\ \times\ .00579\ \tfrac{bbl}{ft}\ =\ \textbf{13.5 bbl}$

Assessment Plug Cementing

1. What is the main advantage of the two-plug method over the balanced plug method?

A .Does not require the use of additional equipment or tools
B .Reduces the likelihood of cement contamination Correct
C .Reduces bottomhole pressure
D .Does not require circulating out excess cement

2. Which of the following are characteristics of the dump bailer method? (Select all that apply.)

A .The dump bailer tool is typically run on wireline. Correct
B .The dump bailer method uses dual wiper darts that displace cement down a work string.
C .The dump bailer method is generally used for setting relatively small volumes of cement slurry at shallow depths. Correct

3. Identify key slurry design considerations for plug cementing. (Select all that apply.)

A .A spacer fluid should be pumped ahead of and behind the cement. Correct
B .Fluid loss control should be tailored to the formation permeability.
C .The slurry should be batch mixed. Correct
D .All cement plugs should use a densified cement.

4. What is the most common method for placing a cement plug?

A .Dump bailer method
B .Two-plug method
C .Balanced plug method Correct

5. Identify reasons why a cement plug can fail. (Select all that apply.)

A .Fluid loss to formation
B .Plug sinks in the wellbore fluid Correct
C .Debris in the perforations
D .Improper setting depth Correct

6. Which of the following are reasons for setting a cement plug in a well? (Select all that apply.)

A .Repair casing leaks from split or corroded casing.
B .Abandon a depleted zone. Correct
C .Complete well suspension or abandonment. Correct
D .Repair mud channels left behind the pipe.
E .Seal off lower intervals in a well so that the well can be sidetracked or recompleted in a shallower zone. Correct
F .Protect weak formations from high pressure operations that may take place in shallower intervals. Correct

7. When applying the balanced plug method, which of the following is a common practice to prevent mud flowing back on the rig floor?

A .Pump the displacement fluid 2 or 3 barrels over full displacement.
B .Pump the displacement fluid 2 or 3 barrels under full displacement. Correct
C .Pump the calculated volume of displacement fluid so that the top of the cement in the drill pipe or tubing is at the desired cement top.

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