Pump down efficiency can be improved by manipulating annular velocity of the bypass fluid. Major factors that affect annular velocity during pump down are: pump rate, line speed, ID of the casing, and OD of the BHA. Utilizing pump ring is the most common approach to improve pump down efficiency, whereas a pump ring can enlarge the OD of the BHA, thus, increase annular velocity.
Without changing line speed and pump rate, BHA with a larger OD will have faster annular velocity than a BHA with smaller OD. However, as annular velocity increase, wireline tension will also increase. To prevent wireline connection breaking from the rope socket, wireline speed should also be increased, in order to reduce and maintain a safe tension range.
As a result, faster line speed can reduce pump down operation time, the faster you get to setting depth, the sooner you can turn off those pumps and save water and fuel.
On the graph below, the blue line and the green line is the actual field data we computed from our job log. It represents the actual line speed and annular velocity, while the BHA was pumped at 3.7bbl/min (start) to 11.3bbl/min (before finish). Therefore, we can assume that under these parameters, the BHA can be safely deployed to the required depth.
The real catch here is how can we improve efficiency while maintaining within safe parameters as mentioned above. By implementing pump ring, we can see that the line speed can be increased as shown by the grey line, while the annular velocity is kept the same as shown by the yellow line. We can also see that the grey line and yellow line comes to a stop earlier than the blue and green line, since the BHA is traveling at a faster speed.
We calculated that in multiple 35-minute runs, if we reduce the annular clearance between the BHA of and casing ID by 60%, we can increase the line speed up to 50%, therefore, shorten pump down time, and save up to 200 bbl of water on average, while maintaining annular velocity, wireline tension and other operation parameters within safety range.
Vertechs Smart Fin is a specialized dissolvable pump ring, that is installed on the sleeve of the adaptor, instead on the plug body. When the plug is set, the pump ring can be retrieved back to the surface with the BHA, leaving zero debris downhole.