A number of components are fitted to the casing string to enable it to be cemented in place. In order to successfully cement each casing string, casing accessories should be installed and the necessary components are listed below;
A float shoe is a short and rounded shape component with non-return value inside which is installed at the end of the casing. The advantages of a float shoe are as follows;
- Prevent mud flowing back while running casing and prevent cement from outside U-tubing back into casing due to unbalanced conditions while performing cementing operation.
- Help running casing to the well. The round shape of a float shoe prevents a casing string from hanging up and guiding a string into a wellbore. Some float shoes are made of high strength drillable material and can be used to reciprocate and rotate to pass any obstructions in a wellbore.
Most oil well cement slurries will be added to some additives in order to modify cement properties so cement operation can be properly performed. In this article, it will cover some of important cement additives in general terms so that it will help you understand the basic function of each additive.
Accelerators are added to shorten the time for cement to properly set and it will reduce rig time while waiting on the cement (WOC). Accelerators are crucial in shallow depths where bottom temperature is low. In the deeper section, it may not require an accelerator, because the well is hot enough and the thickening time will be normal. The WOC time is generally based on the time required to obtain 500 psi compressive strength of the cement.
Chemical used as accelerators are as follows;
- Calcium chloride 1.5 – 2.0 %
- Sodium chloride 2.0 – 2.5%
- Sea water
If the percentage of these additives is high, they will act as retarders instead of accelerators. Continue reading