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Casing Cement Slurry Volume & Weight Calculation

The addition of Cementing additives is one of the variables that influence the base fluid density. This density ought to be gathered for additive concentration when deciding hydrostatic pressure. To assist you with density calculations, this part will provide you with many terms. After completing Cement Slurry Volume Calculation Article, you shall understand the following:

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  • The relationships among density, weight, and volume
  • API gravity
  • specific gravity
  • absolute density vs. bulk density
  • absolute volume
  • cement slurry weight and volume calculations

Density

Density can be characterized as the weight of a substance per one unit volume. In the English system, the  unit of volume is one cubic foot  , and unit of weight is one pound. In the metric system, cubic centimeter (cc) is considered the unit of volume and we use grams as the unit of weight. If you measured the weight of a particular volume of iron, lead, and copper, you would discover they have widely various weights. Accordingly, a term is expected to refer to the weight of a unit-volume of any material — such term shall be called density. For instance, a cubic foot of gold weighs 1206.2 lb, so the density of gold is 1206.2 lb/ft^3. 

If you have the density and the volume of an object, you can calculate its weight: 

Weight = Density × Volume 

Below you will find some densities for your reference.

Solids Liguid & gases Densities
Figure 1

For practical purposes, the densities of gases are contrasted with air at atmospheric pressure rather than with water. Using air as a similar reference, the weights of the gases mentioned above are:

Gas Densities
Figure 2

Specific Gravity

Specific gravity (abbreviated SG) can be defined as the weight of a volume of substance divided by the weight of the same volume of substance taken as a standard. For example, the standard for solids and liquids is water; the standard for gases is air. Another meaning of the term specific gravity is the proportion of the density of a material to the density of water or air. The weight of the water is 8.33 lb/gal. It is a straightforward issue to convert specific gravity to weight (or the vice-versa). 

Problem 

Calculate the specific gravity of a 12 lb/gal brine? 

Solution

SG = density of substance / density of standard 

SG = 12 Ib/gal / 8.33 lb/gal 

SG = 1.44 

If it was given the specific gravity of the brine as 1.44, the density can be determined as following: 

1.44 × 8.33 lb/gal = 12 lb/gal

What Is The Definition Of API Gravity For Cement Slurry Volume Calculations?

Baume’s gravity can be defined as a scale that utilizes salt water as a reference instead of fresh water. It is mainly applicable in refineries to estimate the gravity of acids and alkalis only. API gravity is also utilized in most other materials in the oil field. let’s say again the standard material is the water. Water’s API gravity is considered to be 10 degrees. 

The relation between specific gravity and API gravity is Inverse relationship As one increases, the other decreases. Crude oil with a weight of 42° API gravity has an equivalent specific gravity of 0.82.American crude is commonly in between 0.768 to 0.966 SG, which is equivalent to 52.6° to 10.5° API. 

API readings are standard taken at a temperature of 60°F. Whenever taken at any other temperature, readings must be converted to 60°F to be precise. Tables for this conversion and for conversion of API gravity to specific gravity can be found in the API Standard 2500 bulletin and in various engineering handbooks ( green book, …. ). 

Formulas for conversion are:

Degrees API Gravity = ((141.5 / SP GR)) – 131.5

Specific Gravity = 141.5 / ( API + 131.5)

What Is The Difference Between Absolute Density vs. Bulk Density?

Absolute density can be defined as the mass per one unit of volume. Absolute density use only the actual volume occupied by certain substance. Bulk density can be defined as the mass per one unit of bulk volume – which  incorporates the actual volume of the substance in addition to the volume of trapped “air.” 

What Is The Absolute Volume Used in Cement Slurry Volume Calculations?

Absolute volume can be defined as the volume per one unit mass. Here is a case of absolute volume. It is assumed that there are a container (Fig. 3) which have a volume of 1 cf measures one cubic foot. This container will be filled with ping pong balls. There are empty spaces between such balls, such spaces are filled with trapped air. Let’s calculate the volume in gallons which is occupied by the such ping pong balls only.  

Absolute Cement Slurry Volume Calculations
Figure 3 : Absolute Volume

The volume occupied by the ping pong balls can best be estimated by first determining the volume occupied by the void spaces. To do this, we could add water to the box and it will equal the volume of added water. After obtaining such volume of water required to fill the void spaces, we can subtract it from 7.4805 gal/ft^ 3 to get the volume occupied by the ping pong balls alone. 

The calculated volume of ping pong balls in this way can be called the absolute volume. While this example is overstated, it does assist explain the idea. We in cementing jobs work with sand, cement, etc. instead of ping pong balls, but the balls can be seen as an amplification of sand or cement particles. Void or empty spaces exist in sand; the volume that is added to fracturing fluids is simply the absolute volume of the sand. 

Calculating absolute volume for cement can be streamlined by utilizing the tables for “Physical Properties of Cementing Materials and Admixtures” introduced in the Technical Data section of the Halliburton Cementing Tables (Figure. 4). 

You can see 4 columns, the left-hand (first) column records the substance, the second one lists the bulk weight in lb per ft^3 . The third one provides the specific gravity, and the last one gives absolute volume in gal/lb. 

Note: When fluids are used in absolute volume calculations, you won’t see a gal/lb factor in the  Red Book. Meanwhile, you can have this factor if you have the fluid density in lb/gal. In other words, just divide 1 by the fluid density. For instance, water is 8.33 lb/gal, so: 

gal/lb = 1 ÷ 8.33 lb/gal = 0.12 gal/lb 

Problem 

Calculate the absolute volume (gallons) and weight (lb per gallon) of this slurry? 

  • Base Fluid is water at 8.33 lb/gal 
  • 4 lb of sand is added. 

Solution 

We will use the chart below to help in our calculation of absolute volume. First, record the materials and their densities in the first two columns. After that, open the Red Book table, record the absolute volume factors (gal/lb) in the third column.

Example for cement slurry volume calculation

Multiply the substances (lb) by the factor (gal/lb) to get the absolute volume and then add such values to above table as shown below. For the totals, add the substances (lb) together and then add together the absolute volumes:

Find the desnsity of the mixed slurry using following formula: 

Total lb ÷Total abs gal = lb/gal 

12.33 lb ÷1.1824 gal = 10.427943 lb/gal

casing cementing calculations Red Book data
Figure.4 Red Book data

Problem 

Calculate the absolute volume (gallons) and weight (lb per gallon) of the following cement slurry?

  • Base Fluid is water at 8.33 lb/gal 
  • Additive is 3% KC1 
  • 4 lb of sand is added 

Solution

Total lb ÷ Total abs gal = lb/gal 

12.5799 lb ÷1.1934705 gal = 10.5 lb/gal 

Note: Generally, when working with sand and water (or base fluid) slurries, the calculations are based on 1 gallon of base fluid and the weight of that 1 gallon of fluid.

Sample Problem 

Calculate absolute volume (gallons) and weight (lb per gallon) of this cement slurry volume?

  • Class H Cement Water at 8.33 lb/gal 

Solution 

For the above cementing problem, we will add another column to the chart for mixing water requirements. Proceed as in the two previous example problems until you have to fill in the mixing water requirements for the Class H cement. This quantity you can find in the Technical Data section of the Red Book in the table for “Water Requirements.” For Class H cement, the requirements are 4.3 gal/sk. Enter this under the appropriate column:

example for slurry calculation

Enter 4.3 gal for the absolute volume for water. Divide the water factor by the absolute volume to determine the materials (lb) for water. After that calculate the totals:

example for cement slurry

Total lb ÷Total abs gal = lb/gal 

129.82 lb ÷7.9 gal  = 16.4 lb/gal 

Using this formula, you can find the yield of cement (ft 3 per sack)

Total abs gal ÷7.4805 gal/ft 3 = ft /sk 

7.9 gal/sk* ÷7.4805 gal/ft 3 3 = 1.06 ft /sk 

NOTE: When dealing with cement slurries, the 3 calculations are usually based on one sack of cement and the weight of that sack.

Problem 

Calculate the absolute volume (gallons) and weight (lb per gallon) of this cement slurry?

  • Base Fluid is water at 8.33 lb/gal
  • 4 lb of sand is added. 

Solution 

Using the below chart to assist in such calculation of absolute volume. At the beginning, record the materials and their densities in the first two columns. After that , using the Red Book table, record the absolute volume factors (gal/lb) in the third column.

absolute volumes

Total mixing water shall be entered under absolute gallons before totaling. 

Calculate the weight of the mixed cement by using this formula: 

Total Pounds ÷ Total Absolute gallons = lb/gal 

Calculate the cement yield in cubic feet per sack by using this formula: 

Total Absolute gal ÷ 7.4805 gal/ft3 (constant) = ft3/sk 

The mixing water per sack is the sum of the gallons in the far right column

cement density and yield
Absolute Volume Worksheet
Figure 5 : Absolute Volume Worksheet