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You are right about it being Indian, more specifically South Indian, like most of those polysyllabic names.
Here -
http://en.wikipedia.org/wiki/Venkatachalam
It is explained as a variant of Venkatachalam, but I'm sure it's not from the place name. Several South Indian names incorporate the word Venkat, the name of a hill that is associated with some Hindu god. Venkatachellum appears to be a male given name which refers to this particular deity.