Completing a wellbore in a subsurface formation with packer assembly having first mechanically-set packer as first zonal isolation tool, and second zonal isolation tool comprises internal bore for receiving production fluids, and alternate flow channels. First packer has alternate flow channels around inner mandrel, and sealing element external to inner mandrel and includes operatively connecting packer assembly to a sand screen, and running into wellbore. First packer set by actuating sealing element into engagement with surrounding open-hole portion of the wellbore. Thereafter, injecting a gravel slurry and further injecting the gravel slurry through the alternate flow channels to allow it to bypass the sealing element, resulting in a gravel packed wellbore within an annular region between sand screen and surrounding formation below packer assembly.