ARPO
IDENTIFICATION CODE
ENI S.p.A. Agip Division
PAGE
100 OF 230
REVISION STAP-P-1-M-6100
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Concentration of Additives The concentrations of most solid cement additives are expressed as percentage by weight of cement (BWOC). This method is also used for water. For example, if 30% silica sand is used in a blend, the amount for each sack of cement is 94lbs x 0.30 = 28.2lbs of silica sand. This results in 94 + 28.2 = 122.2lbs total mix. The true percentage silica sand in the mix is 28.2/122.2 = 23.07%. Salt is an exception and is added by weight of mix water (BWOW). Weighting materials are often added on a lbs/sk basis for convenience as it eliminates the need to convert from percentage BWOC to lbs in the bulk plant. Liquid additive concentrations are most commonly expressed in gal/sk of cement. For example, according to table 7.d, liquid sodium silicate has an absolute volume of 0.0859gal/lbs. If a concentration of 0.4lbs/sk is prescribed, the weight of the material is 0.4/0.0859 = 4.66lbs/sk. Material
Absolute Volume
SG 3
(gal/lbs)
(m /t)
Barite
0.0278
0.231
4.33
Bentonite
0.0454
0.377
2.65
Coal (ground)
0.0925
0.769
1.30
Gilsonite
0.1123
0.935
1.06
Hematite
0.0244
0.202
4.95
Limenite
0.0270
0.225
4.44
Silica Sand
0.0454
0.377
2.65
NaCl saturated
0.0556
0.463
2.15
Fresh Water
0.1202
1.000
1.00
Table 7.D - Absolute Values of Common Cementing Materials 7.1.2.
Slurry Density and Weight The slurry density is calculated by adding the masses of the components and dividing it by the total of the absolute volumes occupied, i.e. divide the total weight in lbs/volume in gals.
Pslurry(lbs / gal) =
lbcement + lbwater + lbadditives galcement + galwater + galadditives
The yield of a cement is the volume occupied by a unit plus all the additives and mix water. Cement is measured is sacks therefore the yield is expressed in cubic feet per sack (ft3/sk). This is now used to calculate the number of 94lbs sacks required to achieve the required annulus volume. As there are 31.51 cubic feet per cubic metre, divide the cubic feet by 31.51 to obtain the amount of cement in cubic metres.