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Dr. Syahrir Ridha

Cementing Calculation

The following calculations must be undertaken before cement job performed

1. Slurry Requirement2. Number of Sacks of Cement3. Volume of Mixwater4. Volume of Additives5. Displacement Volume Duration of Operation

These calculations will form the basis of the cementing operation

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1. Cement Slurry Requirement

An additional slurry will generally mixed and pumped to accommodate any errors in the calculated volumes.

It may be due to washouts etc.

Common practice is to add an extra 10-20% of the calculated volumes.

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(Single Stage Cementing Operation)

(Two-Stage Cementing Operation)

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2. Number of Sacks of Cement

1 sack of cement = 1 cu ft = 43 kg = 94 lb

The amount of cement slurry that can be produced from a sack of cement yield of cement

It depend on the type of cement powder (API classification) and the amount of mixwater.

Number of sacks cement required for cement job:

No. of Sacks = Total Volume of Slurry

Yield of Cement

3. Mixwater Requirements

The amount of mixwater required for the operation will depend on the type of cement powder used.

The volume of mixwater required for cement slurry:

Mixwater Vol. = Mixwater per sack x No of Sacks

4. Additive Requirements

The amount of additives is quoted as a percentage of the cement powder used.It used weight rather that volume.This can then be related to the number of sacks of additive.

Number of sacks of additive = No. sacks Cement x % Additive

Weight of additive = No. sacks of Additive x 94 (lb/sk)

5. Displacement Volume

This is the volume of mud used to displace the cement from the cement stinger or the casing during cementing operation

a. Stinger OperationThe displacement volume can be calculated from volumetric capacity of the cement stinger and the depth of casing shoe. The cement commonly displaced by 1 2 bbls of liquid.

Displacement Vol. = Vol. Capacity of Stinger x Depth of Casing

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b. Conventional OperationFor this , the displacement volume is calculated from the volumetric capacity of the casing and the depth of the float collar in the casing

Displacement Vol. = Vol. Capacity of Casing x Depth of Float Collar

c. Two-stage Cementing OperationFor this , the first stage is firstly displaced by a volume of mud (single stage operation). The second stage is based on volumetric capacity of the casing and the depth of the second stage collar.

1st Stage:Displacement Vol. = Vol. Capacity of Casing x Depth of Float Collar

2nd Stage:Displacement Vol. = Vol. Capacity of Casing x Depth of Multi-stage Collar

d. Duration of Operation

It is used to determine the require setting time for the cement formulation. The operation duration is calculated based on the mixing rate for the

cement, pumping rate of slurry and pumping rate for the displacing mud. Contingency Time, an additional period of time to account for any

operational problems during operation ( normally 1 hr).

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EXAMPLE:

Float collar at: 13740

The operation is under Stinger pipe 5 with capacity 0.0997 ft3/ft

1. Slurry volume between the casing and hole?2. Slurry volume below the float collar?3. Slurry volume in the rathole?4. Amount of cement and mixwater?5. Amount of additive?6. Displacement volume?7. Displacement time with mixing & pumping time is 28 ft3/min.

Determine:

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7. Displacement Time

Total displacement time = Time to mix and pump + time to displace cement

Total volume of cement = 1177 ft3 (including additives)

Displacement volume: 5647 ft3

Total volume to mix and displace = 1177 + 5647 = 6824 ft3

Total time @ 28 ft3/min = 6824 / 28 = 243 min = 4 hrs