Born on 5 November 1993 in Tottenham, and having joined the Academy at Under-10, Archange signed a professional contract in July 2011. A central defender who is also capable of a midfield role, he played a part in winning the FA Youth Cup in 2012, making one start and four sub appearances and had regular action in the youth league campaign two seasons running. Having made four reserve team appearances in his first year as a full-time scholar, he was not used at that level in 2011/12.
He went on loan to League One Yeovil Town for a month at the start of the 2012/13 season, and shortly after returning to the Blues it was announced that he would be joining Colchester United until January 2013.
Injuries hampered Nkumu's involvement at Colchester and having failed to make a single appearance for the first team, he returned to Chelsea a month earlier than planned.