Yes, but you wouldn't need to drill a hole to make use of the thermal temperature difference. You can simply take the wire and drop it in the ocean, so that the top is near the surface and the wire end down below. It's a heck of a lot easier to grab a boat and sail it a few hundred miles than it is to drill a hole a mile deep. Or you could just cycle the water itself to do the same thing. (And it is doable. The University of Hawaii built a 10kw plant a while ago, but they didn't go beyond the prototype stage.)