Hydraulic disconnect

A hydraulic disconnect comprising:

• a downhole housing;
• an uphole housing;
• an inner mandrel at least partially disposed telescopically within the downhole housing, the inner mandrel having a latch extendable in a radially outward direction to latch against an inner shoulder of the downhole housing to restrict the downhole housing from relative downhole movement, the inner mandrel being connected for transmission of torque to the downhole housing;
• a piston at least partially disposed telescopically within the inner mandrel and having a latched position in which an outer surface of the piston is radially inward of the latch to maintain latching against the inner shoulder, and an unlatched position in which a groove in the outer surface is radially inward of the latch to allow radial contraction of the latch into the groove for release of the inner shoulder, the piston having a valve seat;
• and
• a lock for maintaining the piston in the latched position, the lock being adapted to unlock in use upon receipt by the valve seat of a disconnect valve member and application of a predetermined hydraulic pressure in a downhole direction against the disconnect valve member to allow the piston to move into the unlatched position;
• in which the uphole housing has a stop for restricting the downhole housing from relative uphole movement and the inner mandrel is threaded to the uphole housing such that relative rotation between the uphole housing and the downhole housing in use tightens the downhole housing between the latch and the uphole housing.