Balanced cement plug is the method to set cement plug by applying concept of balanced hydrostatic. Generally speaking, when we say “balance”, it means that hydrostatic pressure at the end of the drilling string is the same as hydrostatic pressure in the annulus (see the figure below).
(Balance hydrostatic pressure both side)
Some cement formulas have salt as NaCl, and KCl into the cement system and we call them “salt cement systems”. The salt cement systems cause confusion in cement calculations because salt can be dissolved in based fluid and the volume of salt in solid state is not the same as salt in solution phase. Therefore, density of solid salt is not the same as the dissolved salt in liquid.
To get correct density and absolute volume of salt solution, you can find information about from cementing hand books. The books should tell you how much % salt is in solution and how much absolute volume/density is. Please see an image below that I just got from my Halliburton redbook.
This topic demonstrates how to determine cement density and yield as per the cement slurry formula.
The cement formula given from town is listed below:
Cement formula:
Class G cement
35% Silica sand
0.2 gps of chemical A
0.6 gps of chemical B
4.5 gps of drill water
The absolute volume of each material is listed below:
Class G cement = 0.0382 gal/lb
Silica sand = 0.0456 gal/lb
Chemical A = 0.0974 gal/lb
Chemical B = 0.103 gal/lb
This topic will teach you how to determine water requirement (gal/sack) and yield of cement (gallon/sack) as per cement slurry program.
The cement formula given from town is listed below:
Cement formula:
Class G cement
35% Silica sand (35% by weight of cement)
0.2 gps of chemical A
0.6 gps of chemical B
Required cement density = 15.5 ppg
Cement volume calculation is based on annular capacity multiplied by length of cement as per cement program. This topic will demonstrate you how to determine cement volume as per specification and displace volume. After reading and understanding the concept, you will be able to apply to your cement job.
The knowledge required: annular capacity and inner capacity of cylindical object
Well information:
Well is drilled with 8.5 inch bit to 9,015 MD/8,505 TVD with oil based mud (9.5 ppg). Estimated hole sized based on an open hole log is 8.6 inch.
Previous casing size is 9-5/8” and its shoe is at 6,500 MD/5000’TVD.
Plan to run 7” casing and planned shoe depth at 9,000’MD/8,500’TVD.
There is one float collar at 8960’MD/8470’ TVD.
Top of cement is 2000 ft above 9-5/8” casing.
Spacer volume is from top of cement to surface.
Casing information
7” casing ID = 6.185”
9-5/8” casing ID = 8.85”
Use hole size measured from the open hole log to determine cement volume.
The well schematic should look like this.
