crossovers can be installed downhole to allow movement of the fluid from one annular flow channel to another as desired the well completion system 100 uses threaded joints with sliding seals at the lower end of the interior tubing strings of the concentric tubing strings to allow installation and extraction of the underground equipment with surface lifting equipment alone no subsurface grappling or latching equipment is required the well completion system 100 can be assembled into different sections in which the fluid flowing in one annular flow channel may be switched to flow into a different annular flow channel this can allow changing the flow path of hot and cold fluid streams the well completion system 100 can be used to recover heat from a fluid stream control solids precipitation by maintaining fluid temperature use a heated circulating fluid to lower the fluid viscosity of a produced fluid etc the entire underground assembly consists of sections of concentric tubing strings a annular flow crossover is installed at the top and bottom of each intermediate section to redirect the fluid flowing in one annular flow channel into a different annular flow channel if desired each separate section is run by assembling joints of the outside tubing string with threaded connections at each end the bottom section.