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15.2 Thermal Effects
The thermal coefficient of expansion for steel is approximately 1.3 m / 1000 for every 100 o C of warming so it is also possible to estimate from an approximate temperature profile, how much additional depth we will gain from thermal expansion. In the following example of a fairly typical well, there is 2 m of mechanical extension plus 5 m of thermal expansion giving a total of 7 m of additional drillpipe you never knew you had!
Figure 69: Measuring thermal expansion of a typical drillpipe.
This is one of the reasons that wireline measurements and drillpipe conveyed measurements seldom agree. The wireline will stretch much more than steel and when warmed up, oddly, becomes shorter rather than longer due to the lateral expansion of the elastomer within the reinforced sheathing. As a result, wireline is usually corrected for stretch whereas drillpipe almost never is (at the time of writing). Great care should be taken when using drillpipe depths as they will usually be significantly less than actual depth. One commonms k n ssump on s h fw f l oco c fo d llpp s ch n c lplo w ll,w ’llb bl o land a horizontal target at the same depth if also ignore the stretch in that. However, in a vertical well the BHA is supported by the pipe whereas the horizontal wellbore will support the BHA on the low side producing a very different stretch profile.
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