Plug Cementation Variables

1) Nr < 100

1) Low hydraulic horsepower

2) No spacer

2) Low Pressures

3) No retarder

3) Low Displacement rates

4) No thinner

4) Long cementation times

5) No friction reducer

5) Low circulating bottom

The cement bond log which was taken from a plug flow cementation indicates an excellent cement pipe bond. Other points are that the cement to mud transition is sharp, free pipe is clearly shown, and bonded pipe to free pipe signal strength is excellent. The following analysis points out that the cement was in plug flow.

Data is taken from the well log and the power law sheet. The cement properties are those for the class "G" cement.

HEEEE

Top of Cément

Cedent Bond Leg Cement: 200sx, class G, 15.9#/g, — Bonding increases pv a 46c?S/YP = 45*/lQ0sg.ft.

: !

: ' !

— 1-'—r-

Cement displacement rate: 1/2 bbls/r.in

The flow indices for the cement slurry are n = .436 J= 7.5 .01066 * 7.5

1.703

.436

1/2*42

  1. 45 (6.752 - 4.52) The Reynold's number is
  2. 79 r6-75 -4-51'436

.339

2-0.436

15.9

"R

.0713

6000

= 1.125

  • 0.0713 = 0.339 fit/sec
  • 18 = .0889
  • 167 psid

Because the Reynold's number is about 1/5 of the upper value of 100 for plug flow, an excellent plug should form in the annulus and a satisfactory cementation should result.

Turbulent Flow Cementation

The turbulent flow technique gives high displacement efficiencies and is applicable to large volume cementations or where the mud and cement slurry weight are similar. Two critical factors limit its use (1) excessive bottom hole circulating pressures and (2) insufficient surface pump horsepower or pressure. The technique calls for pumping at volumetric rates which places the mud, the spacer which should be used, and the cement slurry which is usually thinned (PV and YP are reduced) all into turbulent flow. Fully developed turbulent flow calls for Reynold's number of 3000 or more.

In all cases the Reynold's number should be calculated with the power law equation.

Turbulent flow cementations are primarily chosen because they require the shortest of all cementation times; and not chosen because of high circulating bottom hole pressures.

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