Here's a survey article from the late 80s which should have a rich references section for you:

Ghiorse & Wilson, https://doi.org/10.1016/S0065-2164(08)70206-5

I think there are two strands: petroleum companies have long been interested in any connection between deep biology and oil; and I think around that time people found microbes in a few sterile-seeming aquifers.

Thanks!