Analysis Of Source Rocks And Geochemical Characteristics Of Oil And Gas In Western Deepwater Area Of Qiongdongnan Basin

In this paper,oil and gas and rock samples from different wells in Qiongdongnan Basin were collected,and the organic geochemistry of macerals,carbon isotopes,geochemical characteristics,distribution characteristics and oil source correlation were comprehensively analyzed.The characteristics of source rocks,oil-gas characteristics and genesis,oil-source relationship and so on are discussed.The average TOC content of Yacheng formation source rocks in the study area is0.5%,and the average hydrocarbon generation potential is 4.7mg/g.The kerogen type is?₂-?type,belonging to high maturity partial?type,humic type and gas generation type;The average TOC content and hydrocarbon generation potential of Lingshui formation source rocks are 4.7mg/g and 3.69mg/g,respectively.The kerogen type is type?₂-?,which belongs to mature partial type?₂,humic type and hydrocarbon generation type.The crude oil in the study area can be divided into the following categories:type A crude oil with high maturity,C₂₇?C₂₉???The R peak is in reverse"V"shape,W/OL>1,OL/C₃₀H>1.5,and steric to Huo ratio<1.Its characteristics are similar to those of condensate around Yanan sag.It has the characteristics of hydrocarbon supply from coal measure source rocks of sea land transitional facies,mainly distributed near well LS13-1-1,and supplied by source rocks of sea land transitional facies of Yacheng formation in situ;Type B crude oil is mature,C₂₇?C₂₉???The peak shape of R is decreasing in a"one"shape,the ratio of steroidal to herbaceous>1,OL/C₃₀H<1,des-A-OL/OL>1.5,9-MP/1-MP is smaller,T/OL>1,mainly distributed around LS18 gas field,and supplied by the shallow marine source rocks of Lingshui formation in the slope zone of Lingshui sag;Type C crude oil is mature,C₂₇?C₂₉???R peak is L-shaped,W/OL ratio is less than 1,OL/C₃₀H is close to 1.It is distributed near L17 and L25 gas fields and supplied by shallow water source rocks in Lingnan low uplift.The maturity of crude oil in different formations of L25 gas field is different from the source environment,and there is mixed source effect or multi-stage oil and gas charging phenomenon.The natural gas in the study area is mainly hydrocarbon gas,mostly dry gas,and wet gas mainly occurs in L25 gas field.Most of the natural gas types are thermogenic gas,kerogen cracking gas and mature high mature coal type gas.The characteristics of L25 gas field are complex,and most of the well gas is mainly thermogenic gas.However,the gas sample of Huangliu formation in LS25-1-5 well has obvious oil type gas characteristics,a small amount of inorganic gas is mixed in,and organic and inorganic CO₂ exists.The natural gas of Huangliu formation in LS25-1W-1 is low mature,and the gas of Yinggehai formation in LS25-1-3 is biogenic gas with low maturity and source of sapropelic organic matter.Inorganic CO₂ in the study area is generally considered to be related to magmatism.