The geochemical exploration for near-surface free hydrocarbons is a geochemical exploration system mainly using the direct detect technology for the free hydrocarbons in soil and combining with the comprehensive application of multiple parameters.

Free hydrocarbon and acid dissolved hydrocarbon samples can be injected directly and separated at field and in laboratory condition.

There are always phenomenons of under -compacted thick mudstones in young and rapidly subsided basins, where massive thick hydrocarbon detained zones are formed due to the difficulty of expelling hydrocarbons with the content of free hydrocarbon as high as over 5000 ppm.