Temperature Effects on Tubing Length Due To Injecting
Heated metal expands, and cooled metal contracts. In a long string of tubing with a temperature change over it’s entire length, this contraction or elongation can be considerable. The three main areas in which you deal with the temperature effects on the tubing strings are:
This subject is primarily dealt with in anchor calculations. Since warmer fluids are brought to the surface through the tubing, this temperature change will always be an elongation. The calculations necessary to figure this were covered in the tubing anchor calculations.
Elongation of tubular goods due to the injecting of steam in a well can be extreme. This is because of the tremendous change in the average temperature of the tubing.
Injecting fluids into a well (as during water floods, frac jobs, and acid jobs which are colder than the well) will shorten the tubing string. This shortening of the tubing can pick a locator seal up out of a permanent packer, or it can rob set-down weight from a set-down packer. With an upstrain tool the shortening can pull additional strain, and perhaps even exceed the minimum yield of the tubing.
These problems can be solved either in the number of inches contraction or elongation, or in pounds up force (contraction), or pounds down force (elongation) due to the temperature change.
The formulas to calculate either inches or pounds force are comparatively simple. But either way, you still need to know the average temperature change of the tubing string. To get this average temperature change, subtract the average temperature of the string when it is at the maximum cooled condition during injection, from the average temperature condition before the job.
To figure the average temperature of a string of tubing, you need to know the temperature at each end of the string. The average temperature is the top temperature added to the bottom temperature and then divided by two. Thus, before the job the average temperature would be based upon the mean yearly temperature and the bottom-hole temperature. (Mean temperature can be thought of as the temperature thirty feet underground which will change very little, and is taken here to be 70° F.)
To figure the average temperature of the string when it is cooled to the maximum condition while injecting, you need to again know the temperature at both ends of the tubing string. The temperature at the top will be the same as the temperature of the fluid that you are injecting. The temperature at the bottom will be dependent upon three things: fluid temperature, injection rate, and injection time period.
The figures on the amount to cool a string for a short pumping job, or for extremely slow pumping are not available. But some of the figures are given so that you will have a guide line. These figures are from several sources, and are reasonably accurate .
Much more to come: