Yes, I must be very uninformed on the topic of producing oil and gas. I hope you can help me learn more.
they drill down 2500 feet
Sometime more, sometimes less. Most of the shale fields are this deep r more.
ground water does not exist below 1000 feet
If you mean potable drinking water, I believe that is true. Too much salt content as you get lower, but there is certainly water lower, it is in the oil/gas fields as well.
For the most part, absolutely correct.
I worked one well in Nevada where we tested and got water with <200 ppm chlorides (fresher than most well water) below 2500 ft. (it looked a lot like oil on the resistivity logs, it was that low in dissolved salts).
Sadly, that was in the middle of the desert on BLM land, and they demanded the oil company plug the well because they did not have a permit to drill for and produce water.
That's one well in a 35 year career with possibly potable water at depths greater than 1000 ft. None of the rest had that.