just had a quick look it appears that there is an overground train (national rail and the company is London Midland) and also underground train (tube) and that you can use Oystercard on both
National Rail Enquiries - Official source for UK train times and timetables for overground rail times and book overground ticket. Probably worth calling for advice +44 871 200 49 50 and to see if you can buy a weekly ticket for the journey.
underground rail times for the journey
http://www.tfl.gov.uk/assets/downloa...-to-euston.pdf
This about using your Oystercard on National Rail
Oyster on National Rail | Transport for London
I don't have an Oystercard so don't know much about how they work.