oil well vs pockmark

oil well

noun
  • A hole drilled into the earth from which petroleum is pumped. 

pockmark

noun
  • A crater in the seafloor caused by erupting gas or liquid. 

  • A mark or scar in the skin caused by a pock. 

How often have the words oil well and pockmark occurred in a corpus of books? (source: Google Ngram Viewer )