The CTDef Software is robust in its ability to model a variety of complex loading situations applicable to sections of tubing in field applications. A front panel enables the user to define realistic load histories “on the fly.” However, there is a more robust “input file” option that is often just as easy and has the advantage that virtually ANY load history can be imposed. The cases listed below are used to demonstrate the capabilities of the CTDef Software for investigating realistic questions about coiled tubing deformation behavior.

1. Influence of Pressure (input using the front panel option)
2. Influence of Tubing Rotation (input using the front panel option)
3. Influence of Reel Back Tension (input using the input file option)
4. Influence of Reverse Bending (input using the input file option)
5. Down-Hole Example (input using the front panel option)

Two technical papers were written to showcase the capabilities of the CTDef Software to the rest of the industry.

1. Influence of Pressure

This project began because of strong evidence of coiled tubing elongation in the field. Simple plasticity analyses, using simple bi-linear uniaxial analysis proved that elongation must occur in the field, for cases of no internal pressure.

However, to analyze the influence of internal pressure on elongation behavior, an incremental plasticity theory was required with a sophisticated implementation algorithm. The CTDef Software delivers this capabilities.

Prior to the start of this project, prominent coiled tubing engineers speculated that pressure might actually inhibit elongation, due to hoop stress effects. Three graphs generated using the front panel input option are presented on the linked pages and the first of these demonstrates that the opposite is true.

In this example, 1.25-in × 0.095-in tubing made of 80 ksi material is deployed with a 96-in diameter spool and a 72-in radius arch. The software was used to simulate 10 trips in and out of a well, with an axial load applied each trip. In this example, axial loads of 10,000 and 15,000 lbs were used (compared to a nominal body yield load of 27,500 lbs) and the internal pressure was varied from 0 to 8,000 psi. Higher internal pressures increase the permanent elongation considerably. On the other hand, the following two graphs demonstrate that the effect of the axial load level on diametral growth rate and the rate of wall thinning are not strong.

The remaining case studies were all run for the physical example depicted below:

Tubing with an 80 ksi yield strength, a 2.375-in diameter and a 0.188-in wall thickness is run into and out of a well 10 times. Each time in and out of a well, an axial force and a fixed amount of rotation may be input. It should be noted that the nominal body yield load for this tubing is over 103,000 lbs. The largest axial load investigated is 80,000 lbs. Prior to this project, none of these load cases would have been expected to impose plastic axial elongation!