1. Actually, in further follow up, oil exists in that 5,000 to 15,000 zone where temps and pressures are "just so." Bit like diamonds, in that way. Coal is the same way --- albeit its sweet spot is higher, and its cooking temp lower.
2. No ones really systematically hunted for "coal" per se at 5,000 to 15,000 (good luck mining at those depths!), so one cannot say that there is not coal co-existent with oil. That said, I would suspect there is coal at depth, compressed and cracked by time, pressure, and temperature. We call such coal "oil."
Hmmmn.
Digging fer coal at 15,000 feet would be a bit tricky!
(But I've never heard of "coal" residue coming up from the mud washed out of oil wells: If it were co-existant, it seems that coal deposits/layers/residues/leftovers/partially-cooked remianed would be mentioned as a regular occurance in the discharges from oil wells.)
I have heard of a few coal deposits that are about 12,000 ft in Wyoming and Colorado - obviously too deep to mine. Candidates for coal bed methane production. I believe the Ute reservation in SW Colorado has one such operation. I think it isn't produced because it's too deep, but I think there may also be other (Indian cultural) factors (IIRC).