5. Tag on Pump ~Downhole Diagnostic (Midland, TX)

These Dyno cards show a well an 8000' well with a Fiberglass + Steel rod string that has a solid 2.5" tag on the pump. The tag is evidenced in the bottom left corner of the pump card where the load sharply dips below the zero-load line (indicating compression). A sharp down-kick can also be seen about 7" into the up-stroke on the Surface Card from the pump tag, meaning if you were standing there at the wellhead feeling for the tag you would not feel it until the Polished Rod had moved up 7" into the up-stroke.
The tag occurs at the bottom of the down-stroke as the bottom of the Valve-Rod Bushing (connected to the bottom sinker-bar) collides into the top of the Valve-Rod Guide (attached to the pump barrel). The reason the tag is felt 7" into the up-stroke is due to the time delay that occurs for the stress wave to propagate all the way up the rod-string to surface (with the pump set 1.5 miles down the well, this takes 0.5-seconds in this example).
After the tag (on the up-stroke), the fluid load is picked up then momentarily lost before being regained. The momentary loss in fluid load occurs at 5.6" into the up-stroke and occurs 1.0 seconds after the tag. This appears to be due to the compressional wave generated by the tag going to surface (in 0.5-sec.) then returning back down the string as a tensional force wave (in 0.5-sec.) that stretches the plunger downward. The plunger is in the beginning of the up-stroke but this downwards stretching wave causes it momentarily compress the fluids in the pump chamber--causing the fluid load to be briefly lost.
This well had several repeated rod failures in the first 6-months of pumping that occurred within the bottom 500' of 7/8" rods (there were 3 x 1.5" sinker bars below the 7/8" rods). The rod parts were always within 2" of the rod up-sets (by the boxes) which is commonly caused by side-loading and bending forces. I think the sharp pump tag had something to do with it.
Notice the upward-right slant of the Surface Card. This type of card is categorized as an Under-Travel Card and indicates the downhole stroke length will be shorter than the input surface stroke length (which it most obviously is). The main reason for this is due to the large amount of Rod Stretch occuring. The well is almost pumped-off (150' of GFLAP) and has 3200' of 1" FG rods with a 1.5" diameter pump. The large pressure differential across the 1.5" pump, along with the high elasticity of the 1" Fiberglass rods makes for a markedly smaller downhole pump stroke. In this instance, down-sizing the pump to an 1.25" would essentially keep the pump systems capacity the same---as the lost production from the smaller diameter pump would be made up for by a longer downhole stroke-length (due to a smaller Fluid Load and thus, less Rod Stretch).
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