from what I know about internships with BP you need a degree therefore you are a good 7 or 8 years off getting an internship with them. some internships you actually you actaully have to pay them to do it (although I am not sure if this is the case with a company like BP) and the few that do pay you pay a stipend therefore is abnout half of what minimum wage is.
over summer I went to south africa and helped at a place called SANCCOB they have loads of oiled penguins and pelicans and stuff come in just from oil normally in the water from boats etc. they have also had to deal with loads of other oil spills in the area. you have to pay a bit to go help them as they are a charity but at your age that experience would be easier to get than to wait to get a degree to work for a disgusting company like BP.
If you live near their offices it may be the case that you could get a week work experience but realistically there will be alot of competition to get this and you are only 14/15.
dont let me put you off though! call them, or if you do live close go down there and ask if there is comeone you can speak to about it.