A method for setting a packer in a wellbore, the method comprising: providing a packer having a packer mandrel with a seal assembly and a piston slidably disposed thereabout; running the packer into the wellbore; resisting a force acting on the piston that is generated by a pressure difference between pressure in the wellbore and pressure in a chamber defined between the piston and the packer mandrel by restraining movement of the piston toward the seal assembly with a frangible member ; characterised in that the method additionally comprises: decoupling a collet assembly disposed about the packer mandrel from a sleeve slidably disposed about the packer mandrel with a liner in the wellbore; shifting the sleeve relative to a packer mandrel extension toward the piston by the movement of the packer causing the sleeve to contact a liner top of the liner ; aligning a fluid port of sleeve with a fluid port of packer mandrel extension , allowing wellbore pressure to enter a fluid pathway and act on the lower surface of piston ; breaking the frangible member coupling the piston and the packer mandrel ; and responsive to the pressure difference, longitudinally shifting the piston relative to the packer mandrel toward the seal assembly , to operate the seal assembly from a running position to a radially expanded sealing position, thereby setting the packer . providing a packer having a packer mandrel with a seal assembly and a piston slidably disposed thereabout; running the packer into the wellbore; resisting a force acting on the piston that is generated by a pressure difference between pressure in the wellbore and pressure in a chamber defined between the piston and the packer mandrel by restraining movement of the piston toward the seal assembly with a frangible member ; characterised in that the method additionally comprises: decoupling a collet assembly disposed about the packer mandrel from a sleeve slidably disposed about the packer mandrel with a liner in the wellbore; shifting the sleeve relative to a packer mandrel extension toward the piston by the movement of the packer causing the sleeve to contact a liner top of the liner ; aligning a fluid port of sleeve with a fluid port of packer mandrel extension , allowing wellbore pressure to enter a fluid pathway and act on the lower surface of piston ; breaking the frangible member coupling the piston and the packer mandrel ; and responsive to the pressure difference, longitudinally shifting the piston relative to the packer mandrel toward the seal assembly , to operate the seal assembly from a running position to a radially expanded sealing position, thereby setting the packer . decoupling a collet assembly disposed about the packer mandrel from a sleeve slidably disposed about the packer mandrel with a liner in the wellbore; shifting the sleeve relative to a packer mandrel extension toward the piston by the movement of the packer causing the sleeve to contact a liner top of the liner ; aligning a fluid port of sleeve with a fluid port of packer mandrel extension , allowing wellbore pressure to enter a fluid pathway and act on the lower surface of piston ; breaking the frangible member coupling the piston and the packer mandrel ; and responsive to the pressure difference, longitudinally shifting the piston relative to the packer mandrel toward the seal assembly , to operate the seal assembly from a running position to a radially expanded sealing position, thereby setting the packer . <EOS>