A thru-tubing completion system comprising: a sub-surface completion unit (SCU) configured to pass through production tubing disposed in a wellbore of a hydrocarbon well and to be disposed in a target zone of an open-holed portion of the wellbore, the SCU comprising an un-deployed outer diameter that is less than an internal diameter of the production tubing to enable the SCU to pass through the production tubing, the SCU comprising: a SCU body having an outer diameter that is less than the internal diameter of the production tubing, the SCU body comprising a down-hole end and an up-hole end , and a central passage extending from the down-hole end of the SCU body to the up-hole end of the SCU body to provide for the passage of substances through the SCU body, the down-hole end of the SCU body configured to be advanced into the wellbore ahead of the up-hole end of the SCU body; and a detachable SCU anchoring seal configured to be positioned in an un-deployed position and a deployed position, the un-deployed position of the detachable SCU anchoring seal enabling the detachable SCU anchoring seal to pass through the production tubing, and the deployed position of the detachable SCU anchoring seal providing a seal between the SCU body and a wall of the target zone of the open-holed portion of the wellbore to provide zonal isolation between a down-hole region of the wellbore located down-hole of the detachable SCU anchoring seal and an up-hole region of the wellbore located up-hole of the detachable SCU anchoring seal, the detachable SCU anchoring seal being releasably coupled to the SCU body and having an internal passage having an internal diameter that is equal to or greater than an external diameter of the SCU body such that the detachable SCU anchoring seal is configured to be deployed in the wellbore and decoupled from the SCU body to enable the SCU body to be moved through the internal passage of the SCU anchoring seal deployed in the wellbore. a SCU body having an outer diameter that is less than the internal diameter of the production tubing, the SCU body comprising a down-hole end and an up-hole end , and a central passage extending from the down-hole end of the SCU body to the up-hole end of the SCU body to provide for the passage of substances through the SCU body, the down-hole end of the SCU body configured to be advanced into the wellbore ahead of the up-hole end of the SCU body; and a detachable SCU anchoring seal configured to be positioned in an un-deployed position and a deployed position, the un-deployed position of the detachable SCU anchoring seal enabling the detachable SCU anchoring seal to pass through the production tubing, and the deployed position of the detachable SCU anchoring seal providing a seal between the SCU body and a wall of the target zone of the open-holed portion of the wellbore to provide zonal isolation between a down-hole region of the wellbore located down-hole of the detachable SCU anchoring seal and an up-hole region of the wellbore located up-hole of the detachable SCU anchoring seal, the detachable SCU anchoring seal being releasably coupled to the SCU body and having an internal passage having an internal diameter that is equal to or greater than an external diameter of the SCU body such that the detachable SCU anchoring seal is configured to be deployed in the wellbore and decoupled from the SCU body to enable the SCU body to be moved through the internal passage of the SCU anchoring seal deployed in the wellbore. <EOS>