I worked in the oil and gas industry maintaining wells to meet the production obligation for over 25 years... Trust me, when we plug a well back, cemented to the surface and cut off the wellhead 3' below grade... it is depleted. That being said the industry as a whole only knows how to recover 20% of overall oil in place (OIP) The industry leaves 80% behind because we are not smart enough to get it out of the ground. Fact.