Command & Conquer: Generals - Zero Hour

I have trouble taking over oil wells so I can make money from them. In the one scenario where you have a lot of oil wells it works I just click on a soldier then mouse over the oil well and an arrow appears and I click on it and soldier goes inside.

On other missions when I try that it does not work. Does it have to be a specific soldier? Do I have to do something to the oil well before I can get a soldier inside it?

Thanks

only the rebel, ranger, and red guard can do it, missle soldiers and others cant.
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BLOOD FOR THE BLOOD GOD!! SKULLS FOR THE SKULL THRONE!!!
XBL Tag: Trooper502