· Gas production from tight shales requires maturation and cracking of oil that has been generated from live organic matter -need to have at least 2 percent TOC to begin with.
· With increasing maturation carbon and hydrogen are lost from shale due to hydrocarbon generation.
· Increasing thermal maturity therefore leads to decrease in TOC and hydrogen values.
· Want shales with decent original TOC, with evidence that significant amounts of gas has formed from that TOC during thermal maturation.