Geochemical Of Hydrocarbon Gas From The Surface Seabed Sediment In BoHai Bay Basin

According to hydrocarbon gas geochemical indicators from sea floor sediments in qi kou sag and sha leitian embossment of Bohai Bay Basin, molecular organization of acidolytical hydrocarbon、pyrolysis desorbed hydrocarbon、top empty hydrocarbon and altered carbonate had been studied.The study found that the top empty hydrocarbon index levels were low,correlation between each other were low,there is a big fractionation effect.Content frequency distribution showed a high after low with unimodal positive skewness characteristics.Hydrocarbon properties analysis showed that the gas is mixture.Both microbial gas and thermogenic gas in there.The content of acidolysis hydrocarbon gas range is small and low, but each acidolysis hydrocarbon gas had been found in the samples.The pertinence between the acidolysis hydrocarbon gas is very well, especially between the adjacent component.Content of the frequency distribution showed positive skewness single-peak or normal distribution characteristics.Isotopes in the frequency distribution is also.Carbon isotope was increased weight with the carbon number.This suggests that acidolysis hydrocarbon gas with the same source.With the increase of carbon number, isotope change interval narrowing, which is a typical characteristic of thermogenic hydrocarbons.The geochemistry field of Acidolysis hydrocarbon in ShaLei tian embossment is medium and average,so qikou sag is.Analysis result of CD-diagram、Bernard diagram 、C1/(C2+C3)—δ13C1 diagram、 characteristics of hydrocarbon gas ratio andδ13Cn~1/n diagram shows that acidolysis hydrocarbon of surface sediments of sha leitian embossment is thermogenic gas,which comprises condensate oil associated gas、coal-derived gas and small oil-associated gas,and so qikou sag is.The content of heat-release hydrocarbon gases are low but intact than the other gases.The variable coefficient is less than one, which belongs to uniform geochemical.Content of the frequency distribution characteristics of the same as acidolysis hydrocarbon gas.The correlation between heat-release hydrocarbon component showed high positive.And the correlation with n-alkanes better than isoparaffin.Due to the contribution of ethene and propylene frompyrolysis hydrocarbon,the denotation of heat-release hydrocarbon methane is not very well.The analysis result of C1—C2crossplot 、 C1/(C2+C3)—C2/(C3+C4) crossplot 、log(C1/(C2+C3))—log(C2/(C3+C4)) crossplot shows that sha leitian embossment belongs to district of air-fuel mixture、deep mixture gas and oil,so qikou sag is.Research data is divided into four groups clustering analysis,according to the clustering analysis of geochemical index of surface sediments in the study area.Acidolysis hydrocarbon methane、heat-release hydrocarbon methane、alteration carbonate and top air methane were selected as the main geochemical indices of research area after integrating optimization of geochemical indicators. The relationship between anomalies distribution of geochemical indices and structure and oil and gas fields of research area indicate that anomalies distribution of geochemical indices in the seabed sediments is the result of deep vertical percolation of hydrocarbon reservoirs and micro leakage faults.Distribution characteristics of geochemical indices is controled by reservoir strata, sealing performance of reservoir caprock and fracture systems.The edge and the top abnormity was caused by vertical seepage of reservoir.The leakage of fault and unconformable surface leads to the abnormity of fracture system, which confirmed a fault on the seal of the reservoir from the side by the way.Abnormal distribution of geochemical indices is around oil-gas field like a loop or half loop,which shows that reservoir cap plays a decisive role on plays a decisive role and geochemical anomalies in spatial distribution.Headspace gas methane has the most closely relationship between oil-gas fields.Headspace gas methane could be the best geochemical index as the next exploration in the study area.The loop of heat-release hydrocarbon methane and hydrocarbon acidolysis methane is most complete,whose corresponding relationship with oilfield is most obvious.So the heat-release hydrocarbon methane and hydrocarbon acidolysis methane could be the secondary indicator.The instruction significance of altered carbonate is not good enough for the distribution of oil-gas reservoirs,which could be the supplement of the other geochemical indices.