Standard Circulating tool with a BHA Disconnect module installed
The AVD is very similar to the AVS but has a unique BHA disconnect module that allows the Operator to disconnect the drillstring from the BHA if the BHA becomes stuck. The AVD uses its onboard sensors; pressure, accelerometers and MEMS gyro to establish that it is stuck. It then moves through a process of software modes, which are fully customizable, before putting itself in a position to receive the disconnect command from surface.
A pre-defined “morse code” signal is sent from surface by moving the drillstring up to full tension
and then back to compression.
The AVD reads this and powers its electrical motors to activate the mechanical clutch. The upper AVD and BHA can be retrieved. The whole disconnect procedure is under the control of the Operator and no specialist personnel or equipment is required. The Disconnect process is depicted in the chart below.
The Hookload, block position, flow and RPM sensor readings are taken from an actual Stuck Pipe incident. The text boxes indicate how the AVD would have interpreted the situation and the modes the tool has to travel through before being able to receive a Disconnect command from surface.
(Click image to enlarge)