On the face of it, even if we were (as wholly unlikely as it is) to forgo any claim on North Sea Oil, it still isn't viable.
The only way I could imagine it working is if an independent Scotland went down a Singapore/Irish fiscal route, whereby they whore themselves out as a foreign investment honeypot. But with stiff competition from the remainder of the UK speaking the same language, with a greater labour pool and better general infrastructure, they'd need to be offering mad tax incentives.
All conventional economic and business wisdom points to the fact that it would not be possible, at least not at any time in the near future.