Geochemical investigation for oil and gas in middle sag of Bohai Basin

The geochemical investigation for oil and gas in middle sag of Bohai Basin was done. Petroleum hydrocarbons of benzene, toluene and δ~(13)C_1(~(13)C_1/~(12)C_1) in different matrices such as sediment, slurry gas were determined using gas chromatograph-mass (GC-MS), micellar electrokinetic capillary chromatography (MECC) and laser frequency modulation absorption spectroscopy. The mean volume fraction of benzene and toluene is 0.107×10~(-6) and 0.130×10~(-6) in sediment respectively, 0.844×10~(-6), 0.195×10~(-6) in slurry gas respectively and δ~(13)C_1 is -21‰～-72‰. The results indicate that the contents of benzene and toluene become high on the top of reservoir formations of 300 meters. The oil and gas survey results were tested by three oil wells, three oil and gas wells and two gas wells. The natural gas originated from oil and coal reservoir formations mainly, a little from biogenic gas and deep gas reservoir formations.