Actually there are significant differences between them. 起初 = at first 原来 = used to e.g. 我起初不喜欢她. = I didn't like her at first (but I liked her LATER) 我原来不喜欢她. = Ｉdidn't use to like her (but I like her NOW) In addition, as you may know, 原来 has another meaning: It turned out that .... e.g. 原来是他干的.

起初（≈一开始的时候）：at the start（usually refer to a shorter period compared to the current condition） 起初我觉得中文很难，现在觉得很简单。 At first, I felt Chinese difficult but now I feel it easy. 原来：1（≈本来） formerly; originally, （emphasizing the difference） Formerly he worked on a farm , but now he ' s a teacher . 以前他在农场工作，但现在是老师。 2 （≈其实、事实上）actually; as a matter of fact（compared to a false impression） She looks young, but she's actually 60. 她看起来很年轻，原来已经六十岁了。

起初，At the very beginning 原来，It turns out to

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: 他为什么能在这么短的时间内完成这项工作呢？ 原来有人在帮他。 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