Source Composition,Hydrocarbon Generation Potential Of Source Rocks And Its Control On Hydrocarbon Accumulation In Yingqiong Basin

In this thesis,the hydrocarbon generation potential of Miocene and Oligocene source rocks were comprehensive evaluation,the organic petrology characteristics of different source rocks were studied by the first application of whole rock analysis,the source composition of source rocks were quantitative researched,the depositional environment parameters of DBT/P,fluorine series and the maturity parameters of MPI1,4,6-DMDBT/1,4-DMDBT and 2,4-DMDBT/1,4-DMDBT of aromatic were developed,the control on hydrocarbon accumulation in high temperature and high pressure gas field were studied,by using the theoretical knowledge of petroleum geology,Oil and gas geochemistry,organic petrology as well as the analysis technology of Rock-eval pyrolysis,maceral identification,saturated hydrocarbon chromatography and chromatography-mass spectrometry,aromatic hydrocarbon chromatography-mass spectrometry.The organic matter abundance of Miocene and Oligocene source rocks in the YingQiong Basin are generally low,the TOC of most source rocks range from 0.3%to 1.0%,and the TOC of Qiongdongnan Basin source rocks are relatively high than Yinggehai Basin source rocks.The organic matter abundance of different formation source rocks from high to low in Yinggehai Basin are Meishan formation,Sanya formation and Lingshui formation.The TOC of Meishan formation source rocks in L-1X,L20-1,L20-2 are obviously lower,the average value are all below 0.45%,whereas the average value of TOC of L22-7 source rocks are up to 2.07%.The organic matter abundance of different formation source rocks from high to low in Qiongdongnan Basin are Yacheng formation,Lingshui formation,Sanya formation and Meishan formation.The average value of TOC of Yacheng formation source rocks from the Y13-2,Y13-4,Y13-6 in Yanan depression and the Y2-1 in Songnan low uplift are up to 0.9%.Organic matter type of source rocks are roughly consistence discriminated by rock pyrolysis parameters,whole rock maceral composition and element composition of kerogen.organic matter types are mainly typeⅡ₂ andⅢof different formation source rocks.Vitrinites in YingQiong Basin source rocks are the predominant maceral and are present as collinite and vitrodetrinite,while telinite is rare.Inertinites are present as fusinite,semifusinite and inertodetrinite.Exinites are present as sporinite,cutinite and liptodetrinite.The sapropelinites are mainly alginate and mineral bitumen groundmass.The maceral contents of source rocks from Meishan formation are higher than Sanya formation and Lingshui formation in the Yinggehai Basin,meanwhile Yacheng formation and Lingshui formation are higher than Meishan formation and Sanya formation in the Qiongdongnan Basin.The wells in Yinggehai Basin with higher maceral contents of source rocks from Meishan formation are D1-11,L20-1,H29-2,LT35-1 and LT26-2,and the average value of the maceral contents of the Yacheng formation source rocks in Y13-3 is up to 1.9%.The maceral composition of the studied samples are dominated by vitrinites,and the contents of inertinites were relatively lower,characterized by the dominance of terrestrial organic matter.The main hydrocarbon generating components of source rocks from the YingQiong Basin are liptodetrinite,alginate,sporinite and mineral bitumen groundmass.Bitumen“A”group composition of YingQiong Basin source rocks characterized by high content of saturated hydrocarbon and low content of aromatic hydrocarbon.Theδ¹³C of Bitumen“A”,saturated hydrocarbon and aromatic hydrocarbon of Meishan formation source rocks are lighter than Sanya formation source rocks.Theδ¹³C of Bitumen“A”,saturated hydrocarbon is light and theδ¹³C of aromatic hydrocarbon is heavy.The biomarker of Meishan and Sanya formation source rocks from YingQiong basin are characterized by predominance of low molecular weight homologues,pristane occurs in higher concentrations than phytane,high abundance of terrigenous terpane,and deposited in weakly oxidizing to weakly reducing environment.The biomarker of Lingshui and Yacheng formation source rock from YingQiong basin are characterized by high Pr/Ph,high abundance of oleanane and C29Sterane and deposited in oxidative depositional environment.Aromatic hydrocarbons are dominated by conventional polycyclic aromatic hydrocarbons,with high content of phenanthrene and naphthalene,detect chrysene,perylene,pyrene and benzopyrene.The main component of aromatic hydrocarbon of Lingshui and Yacheng formation source rocks are phenanthrene,chrysene and naphthalene,and the main component of aromatic hydrocarbon of Meishan and Sanya formation source rocks are phenanthrene,chrysene,pyrene,Fluoranthene,benzopyrene,naphthalene.The thermal evolution of organic matter of source rocks in YingQiong Basin are mainly in the mature stage.（The Ro of most studied samples are range from 0.5%to1.3%）.The Ro of different formation source rocks from low to high in Yinggehai Basin are Meishan formation,Sanya formation and Lingshui formation,range from0.23%to 1.04%,indicate the degree of thermal evolution is in the immature-mature stage,most of samples in the oil window.The Ro of each well increase with the increasing of buried depth.The degree of thermal evolution of each well in Qiongdongnan Basin reached the mature stage,and profitable to the generation of hydrocarbon.The Ro of different formation source rocks from low to high of each well in Qiongdongnan Basin are Meishan formation,Sanya formation,Lingshui formation and Yacheng formation.Parameter of saturated hydrocarbon and aromatic hydrocarbon biomarkers such as C29ββ/（αα+ββ）,C29 20S/（20S+20R）,MPI1,4,6-DMDBT/1,4-DMDBT can well characterize the thermal evolution of the source rocks in YingQiong Basin.Use the content of organic carbon,the maceral content and the potential of hydrocarbon generation amount as the evaluation index,Meishan formation and Sanya formation source rocks in the Yinggehai Basin are middle source rocks,and Lingshui formation source rocks are poor source rocks.Yacheng and Lingshui formation source rocks in the Qiongdongnan Basin belong to middle-good grading,Sanya and Meishan formation source rocks are relative poor.Meishan formation source rocks have the best hydrocarbon generation potential in Yinggehai Basin,which characterized by high abundance of organic matter,Ⅱ₂ andⅢorganic matter type,medium thermal evolution and large thickness.The abundance of organic matter of Sanya formation source rocks is lower than Meishan formation source rocks,the organic matter type isⅡ₂ andⅢ,the thermal evolution is mature,the thickness of strata in the central and southwestern parts of the basin is large.Sanya formation source rocks have relatively good hydrocarbon generation potential.Yacheng and Lingshui formation source rocks have high abundance of organic matter,organic matter type isⅡ₂ andⅢ,the thermal evolution is mature to over mature,the thickness of source rocks of the Yacheng formation is large,Yacheng formation source rocks have the best hydrocarbon generation potential in Qiongdongnan Basin.Meishan and Sanya formation source rocks have certain hydrocarbon generation potential,which characterized by relatively low abundance of organic matter than Yacheng and Lingshui formation source rocks,Ⅱ₂ andⅢorganic matter type,low to medium thermal evolution.The composition of natural gas is complex and the content of main components varies greatly in Yinggehai Basin,while relatively simple in Qiongdongnan Basin,which are mainly hydrocarbon gas.The methane carbon isotopes of natural gas of D1-1 gas field and LD22 gas field in Yinggehai Basin are roughly equivalent to the main frequency ratio of methane carbon isotopes in large and medium gas fields in China,while the methane carbon isotopes of natural gas of Y13-1 gas field,B19-2 gas field,and L22-1 gas field in Qiongdongnan Basin are relatively light.Carbon isotope reversal phenomenon rarely found in natural gas of YingQiong Basin.The hydrocarbon gas of Yinggehai Basin divide into thermogenic gas,biogas and mixture gas,most of the hydrocarbon gas is thermogenic gas,biogas mainly found in LD22gas field and mixture gas mainly found in LD22 gas field and D1-1 gas field.The hydrocarbon gas of Qiongdongnan Basin is dominated by thermogenic gas.Source rocks control action on hydrocarbon accumulation in high temperature and high pressure gas field in the Miocene and Oligocene source rocks from YingQiong Basin were summarized by source rock distribution,abundance and type of organic matter in source rocks,thermal evolution characteristics and generation intensity of source rocks,including the large area,continuously distributed and thick of source rock,high abundance of organic matter and available to produce gas,appropriate thermal evolution degree,high temperature and high pressure environment,high generation intensity.The source rocks of the Ledong-Lingshui depression in Qiongdongnan Basin are characteristized by high thickness,high thermal evolution and high generation intensity,which have a good potential of hydrocarbon generation.