Abstract
Evolution of coiled tubing services requires greater down-hole depth accuracy. Depth critical jobs include coiled tubing conveyed perforating, zonal isolation and plug setting, among others.
Coiled tubing depth measurements are performed at surface, using devices to measure the length of coil tubing being deployed in the well. Measurement methods and their procedures have varied over time and have been continuously developed and improved on in an attempt to achieve higher degrees of accuracy and reliability in the length measurement. By principle, these methods provide a measurement of the length of the pipe deployed into the well but may considerably differ from the true depth of the coil end due to down-hole deformation of the coil tubing.
Various factors influence the down-hole deformation of the coil tubing; among these factors are temperature and pressure effects on the pipe. Elastic deformation of the pipe due to its own weight, sinusoidal and helical buckling effects occur and can substantially affect true depth. In view of this complexity, down-hole depth correlation is executed in depth critical jobs using various techniques, such as; tubing end locator, wireline logging tools, memory runs and reference depth tagging technique.
This paper discusses the different methods of surface pipe length measurement, their historical developments and the errors in true depth from measured depth due to down-hole deformation of the coil tubing. We present the results of a newly developed tool, DepthLOG, that provides a reliable and accurate down-hole depth correlation without the drawbacks and expense of other currently used down-hole depth correlation runs.
