Tandem circulating tool used in conjunction with AVS or AVD for the Tandem Hole Cleaning Protocol
The AVT is run in conjunction with the AVS (or AVD) under the command protocol called TANDEM. This application is aimed at cleaning long open hole sections using two AV tools as depicted in the diagram below. The AVS is run in the BHA and the AVT is run in the drillstring, ideally at the base of a build up section.
The AVT has two positions, throughbore and bypass. In the bypass position, there is no full closure ball valve.
When the Tandem downlink command is sent, the two tools respond in different ways. The AVS tool in the BHA moves to the bypass position and the hole clean up begins. The Operator can keep pumping at maximum rate through the 4in² TFA of the AVS and move the cuttings up the hole towards the AVT. When the cuttings are above the AVT, the pumps are stopped allowing the AVT to move to the bypass position and the AVS to move to the throughbore position. The pumps are restarted and the cuttings continue to be pumped up the hole from the AVT position.
This allows for a tremendous increase in AV as the drillstring pressure losses are vastly reduced because there is very little flow going below the AVT. The cuttings can be removed from the hole at a much faster rate and the overall ECD is reduced as the drillstring below the AVT is not being circulated.