Not an economist, but:

As a result, the hunt for oil went to technical and geographical extremes like shale oil in South Texas, tar sands in Alberta, deepwater sites in Brazil and offshore wells in the Arctic. And the hunt became more expensive: The break-even point for many unconventional projects was $70 or more per barrel.

"Unconventional projects" tend to be executed in environments with fewer environmental regulations. The rise of oil prices brought an increase in refinery capacity in the United States, not in exploration (fracking is largely about natural gas, a separate economy). After Deepwater Horizon, there's a moratorium on deep drilling in US waters. Light sweet crude is hovering around $50 a barrel right now. Which means right now, Shell loses $20 a barrel on shit like ANWR, deepwater drilling and the like.

Also, environmental regulations aren't relaxed in times of cheap oil. The incentives to produce as cleanly as possible remain, while powerful disincentives to sporty exploration appear.

Finally, institutional energy prices rarely drop: ConEd is going to charge you the same regardless of whether or not oil is cheaper for them. Southwest and United aren't going to cut you a break on fares just because their gas is cheaper; in fact, they've likely locked in prices long-term (Southwest did this in '08 which allowed them to ride out the recession sitting pretty). So the incentives to use more fuel are greatly diminished.

I would guess that low oil prices are better for the environment, but it's a guess. Harvard seems to think the sweet spot for the environment is between $60 and $80 a barrel.