Abstract

The need to know when surface casing or intermediate casing has been worn beyond its critical thinning point is always a concern of Operating Personnel. Drill pipe can wear a groove in the casing where the tool joints rotate. This groove is not always on the low side of the casing. The wear groove can be on any side of the casing due to doglegs in the wellbore, or it can be on the top of the casing depending on the deviation of the build angle at the kick off point of the wellbore. Casing wear is not only a function of how long the drill pipe rotates in the casing, but also a function of how rough the tool joints are and the amount of force pressing the tool joints against the casing.

The Ultra Sonic casing measurement is run at the same time as the cement evaluation log and will determine if there is any drill pipe wear inside the casing and establish a base log for future use. The Ultra Sonic casing measurement is taken every five degrees (72 measurements per level) in circumference around the casing and is presented as an image. This gives a total evaluation of the casing from the top to the bottom of the well. Measurement of the internal radius and thickness of the casing allows metal lost on the inside and outside of the casing to be determined.

Three examples are included in this paper to show how the Ultra Sonic casing measurement helped lead to decisions which saved the company several hundred thousand dollars by eliminating the need to run an extra string of casing to protect the intermediate casing after the well was drilled.