Note: I have done considerable research on this topic and have not yet found an answer that fits the specific conditions of my question. Since my question has unique conditions, (for example: The oil company does not want to spend any money on not damaging the environment, whereas most real companies do.), I think that it is both suited to worldbuilding (As the conditions are unique and fictitious.), and that Stack Exchange is an easier way of getting an answer than the alternative (Compiling a large amount of research from many sources, plus some educated speculation as well probably.) There is also no other SE site I could ask this on (Because of the speculative/fictional conditions, it would be very specific for Earth Science.SE or some other site.) If you agree, I would be grateful if you voted to re-open this question.
My island is in the Indian Ocean. I'm not sure what size it'll be, but at least 10,000 square kilometers, maximum 40,000. It's covered in jungle and tropical savannah, and highly biodiverse. It contains species, including megafauna, not found anywhere else, but has no human habitation.
So, if a very very powerful oil company wanted to tap the abundant oil reserves, and planned to build a large oil drilling facility there, what damage would it do to the ecosystem?
The facility includes: Heavy equipment for extracting the oil, large (but cheap and portable) containers for the oil, accommodation for the workers, a runway for big cargo planes to transport it, an electric fence around the facility for keeping out dangerous wildlife, and a garage for reconnaissance vehicles (With the appropriate equipment to locate large oil deposits.) All the facilities will be as cheap as possible, provided that they do the job as profitably as possible.
The company will not be concerned about the damage to the ecosystem, so will extract the oil in the cheapest, most profitable way possible.