There's more. At the same time oil well holes are drilled many orders of magnitude deeper making them cross thousands of strata rather than being limited to a meter or two. Most oil drilling is in areas prone to subduction but there are areas in Canada where they're drilling over surface rocks that are hundreds of millions of years old. Those won't subduct soon and are far more discoverable than an animal burrow due to size. We've got around 1 million active oil wells in N. America, fewer than animal burrows, but in areas they'll be preserved in deep time and in sufficient numbers there's a reasonable chance of discovery.