In rod lift wells there are lots of things often rubbing on each other and sometimes they rub each other the wrong way. Sucker rods rub holes in tubing strings and wells quit pumping, or pump poorly, or pump oil and water emulsions that can be "cut" so badly the fluid at the surface looks like yellow baby shit. There are all kinds of ways to determine if the tubing has a hole in it but in the end sometimes you have to just pull the entire string and "paint out."
Once the rods and bottom hole pump are all pulled out of the hole, painting out involves pouring a gallon or so of aluminum paint down the tubing. You pull each joint looking for where the aluminum paint has leaked outside the tubing string, indicating a hole. Most of the time it will show up very nicely. In this case, above, bright silver paint was all over the outside of joint no. 48 and on further inspection the hole was found. . Actually it was a long "split" as a rod box traveled up and down in the tubing and wore it paper thin. When we took a hammer to this hole it split another 4 inches (you can actually see where the tubing is cracked). This joint was replaced and the entire tubing string run back in the hole, some worn rod boxes were changed out and some rubber rod "guides" were run in this area to prevent this from happening again.
"Painting out" is about as old as the oilfield. It works.
5/8ths in. OD sucker rods with pins (male) and boxes (female). Above each pin or box is the rod "shoulder" where rod wrenches are placed to make up or break out the rod connection. Sucker rods are always exactly 25 feet long. In this photo you can also see rubber rod guides placed on the rod that help prevent holes from being rubbed in the tubing. No holes drilled in the ground are perfectly straight; the can be a little wavvy or sometimes damn right crooked, with actualy dog legs in them. Shale oil wells are drilled so fast they often look like corkscrews with kinks in them and the placement of rod guids to help prevent tubing wear is an exact science. There are even engineers that specialize in exactly where to place rod guides in shale oil wells.
This endeth the lesson of the day.
Mike Shellman, PhD.
(post hole digger)