Routine reports with the results of multifinger tubing caliper surveys normally provide a very basic view on the corrosion attack in which only one Or two data points per joint are given.

A computer model has been developed which allows the use of all digitised data available from both computerised data acquisition systems, the ‘electric’ caliper, and data from the video image decoder reading the caliper stylus imprints on a metal chart, the ‘mechanical’ caliper.

These data sets are used to verify the performance of the caliper tools by checking the response of the individual feelers, Checking the eccentricities and making necessary corrections if required.

Plotting routines are available to study in detail images of pits, lines of pits, wireline grooves, ring corrosion, damage to connection make-up or tubing accessories such as safety Valve landing nipples and wireline profiles.

The results of these detailed studies can give an early indication of possible corrosion problems with equipment or with the methods used and can subsequently lead to preventive or corrective action.

Probability plots from critical areas are used to monitor and predict corrosion progress and subsequent reduction in wall thickness and remaining strength. This together with production forecasts and flow parameters are used to calculate the prevailing pipe body stress at any given moment in time. These values can be shown in the von MISES load ellipse for the corroded tubing. A cut-off criterium of 80% of minimum yield stress can used and when predicted the tubing should be listed for replacement.

This decision support system can be used to provide an overview of

  • planning of future caliper surveys

  • work-over requirements e.g. rigs, tubulars, accessories etc.

You can access this article if you purchase or spend a download.