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Cerberus for FEA Snubbing and Modeling
Cerberus™ FEA Engine
Software
The Cerberus FEA Engine is a highly flexible engineering tool for performing various types of buckling calculations.

Performs buckling calculations of a pipe inside a wellbore or pressure-control stack. This software is intended for engineers, and uses Excel as the user interface. A user must have an engineering background and a working knowledge of Excel to use the software.

The example on the right demonstrates the capabilities of the software. 2-3/8" tubing with a 4-3/4" packer is being snubbed into a well through a stripper. The stripper appears as a purple horizontal line. The pressure below the stripper is 5,000 psi, and there is 4,400 lbs of stripper friction. At the top and bottom of the packer there is a thread relief, causing higher stresses in these areas. As the BHA moves downward it buckles until the packer contacts the 7 1/16" ID lubricator. There is a significant wall contact force (WCF) at the point the packer touches the lubricator. The first 2 plots show the string (red) inside the well control stack (black), looking at it from the Y and Z directions. Note that the vertical direction is X. Also note that the scale length of 50' in the X direction and ±4" in the Y and Z directions causes the string to be distorted. The third plot shows the maximum radial displacement (RD) along the length of the string. This RD may be at any rotational orientation. The fourth plot shows the wall contact forces. There is a spike in the wall contact force where the packer touches the lubricator. The fifth plot shows the maximum Von Mises stress and the yield stress. In this case there is a point at about 14' in which the Von Mises stress exceeds the yield stress, and thus the string would likely bend.

Body Images
Body Images

The model can also output values versus time, as shown in the following figures.

The maximum Von Mises stress along the entire length of the BHA is shown versus time. The buckling continued for the first 5 seconds but then stopped as the packer approached the stripper. The sharp increase in compressive force and Von Mises stress near the end of the simulation occurred as the bottom of the packer was pushed into the stripper. The following figure shows the corresponding displacement and compressive force.

 

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