the casing and tubing the casing extends into a formation 20 which contains hydrocarbons such as oil or gas a cement sheath holds the casing in place in the hole which has been drilled in the ground the tubing has a bore 24 together the annulus 16 and the tubing bore 24 form the wellbore packer 28 is positioned between casing 12 and tubing 14 to seal annulus 16 fluid may be inserted into the annulus 16 between the tubing and the casing above the packer 28 in order to reduce the difference in pressure between the formation 20 and the inside of the casing located downhole of the packer 28 is bar actuated vent 42 shown in more detail in fig9 vent 42 is in the shape of a hollow cylinder with a pin 46 extending into the interior of the vent ports 50 permit fluid communication between the interior of the tubing and the annulus 16 in fig1 and 9 vent 42 is in the closed position in the closed position sleeve 54 obstructs the ports 50 in the vent 42 and prevents fluid communication with the annulus 16 as described below vent 42 may be opened by breaking the pin 46 after which spring 56 causes sleeve 54 to move upwards into recess 58 until shoulder 60 prevents further upward movement of the sleeve 54 in this open position ports 50 are unobstucted by the sleeve 54 so as to permit the displacement of wellbore fluid it can thus be seen that vent 42 can replace a standard surge tool and results in the tubing being kept dry the vent 42 can be.