The oil depletion allowance (curtailed since its glory days) was a major one, at some point allowing the deduction to continue way past the original well investment was recuperated.

As far as the modern state of tax incentives - https://www2.deloitte.com/content/dam/Deloitte/us/Documents/... and discussion of the current carveouts https://www.wsj.com/articles/does-the-oil-and-gas-industry-s...