起初：first of all
原来：present a past fact which doesnt exist any more
for example, 原来他有有钱，但他现在很穷。he was very rich but now he is poor.
原来 has another important meaning: to lead a reason:
why can he finish this job in such a short time?
because someone helped him.
ofc, u can also use 因为有人在帮他 but 原来 highlights the reason and the question.
I really really really want to know the reason.
another example, u can find ur key. then u start to find that. but u cant. then ur bother comes back and tells u that he took ur key accidently, then u can say:原来钥匙在你那里啊！(in english, we say: oh! here it is!)--------attention: here, u can just use 原来 u can't use 因为,because there is no question, u just highlight the result.
so for 原来：
原来 = 起初
原来 = 因为 plus it highlights the question and the response
原来 leads also a fact which really question u. in this case u can replace it by 因为