AVT – TANDEM Application
The AVS is fully programmable and because of this, 2 x AVS tools can be run in the drillstring and commanded separately from each other. This allows for a TANDEM application particularly suited to long highly inclined or horizontal wells where 2 x AVS’s are strategically placed to effect rapid wellbore clean up with the lowest ECD. The secondary AVS usually placed in the drillstring is called the AVT.
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 a simple programme loaded that will get it into Full Bypass quickly when required. The animated graphic shows the principle of operation.
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 and the AVT commanded into the Full Bypass 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 no 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. If desired, the ball valve which closes in the AVT when moved to the Full Bypass position can be nozzled to allow a small percentage of flow to the BHA and bit.
The video shows 2 x 7” AVS tools setup on our flow loop and the flow being alternately switched from one to the other.