鄂尔多斯盆地中部三叠系延长组7段烃组分的运移分异作用

Migration differentiation of hydrocarbon components in the 7th member of the Triassic Yanchang Formation,central Ordos Basin

鄂尔多斯盆地延长组7段页岩体系是泥岩、页岩和砂岩的组合体。为了深入揭示页岩油组分在不同岩性中的运移分异现象,针对鄂尔多斯盆地中部地区开展了典型烃类组分的运移分异研究。研究表明:在不同的岩性中4类族组分含量存在差异。砂岩中饱和烃(SAT)含量高,非烃与沥青质(NSO+Asph)含量低。页岩和泥岩的SAT含量低,NSO+Asph含量高。砂岩的n C_(11-15)烃类组分含量较高,nC_(23-39)烃类组分含量较低;页岩和泥岩的nC_(11-15)烃类组分含量较低,nC_(23-39)烃类组分含量较高。页岩和泥岩的Pr/Ph,Pr/nC_(17)和Ph/n C_(18)等含量比值参数数值变化大,砂岩的数值变化小。页岩和泥岩的C_(27)/C_(29)规则甾烷含量比值较低,砂岩则较高。页岩和泥岩的藿烷Ts/Tm与Ts/(Ts+Tm)比值较低,砂岩则较高。页岩和泥岩的C_(32)升藿烷22S/(22S+22R)比值变化较大,砂岩则具有相对集中的数值。砂岩的伽马蜡烷指数较高且数值分布范围较广,而页岩与泥岩则相反;页岩和泥岩8β(H)-补身烷/8β(H)-升补身烷的含量比值普遍大于1,而砂岩的数值普遍小于1。综合研究认为,不同石油组分在烃源岩内部的分布差异是吸附差异和不同石油组分运移分异共同导致的。

The shale sequence of the 7^(th) member of the Yanchang Formation (also referred to as the Chang 7 Member) in the Ordos Basin consists of mudstones,shales,and sandstones.To delve into the migration differentiation of shale oil components in different lithologies,we investigate the migration differentiation of typical hydrocarbon components in the central Ordos Basin.The findings show that the rocks exhibit different contents of the four group components:saturated hydrocarbons (SAT),aromatic hydrocarbons (ARO),polar nitrogen-,sulfur-,and oxygen-containing compounds(NSO),and asphaltenes (Asph).Specifically,the sandstones manifest high SAT content and low NSO+Asph content.Conversely,the shales and mudstones exhibit low SAT content and high NSO+Asph content.Regarding n-alkanes,the sandstones demonstrate high n C_(11-15) content and low nC_(23-39) content,while the shales and mudstones display low nC_(11-15)content and high n C_(23-39) content.Compared to the sandstones,the shales and mudstones show more significant variations in the Pr/Ph,Pr/nC_(17),and Ph/nC_(18) ratios.These rocks manifest low C_(27)/C_(29) regular sterane ratios and low Ts/Tm and Ts/(Ts+Tm) ratios,while the sandstones show opposite trends.They demonstrate substantial variability in 22S/(22S+22R) ratios for C_(32) homohopane,in contrast to the relatively concentrated ratios for the sandstones.Besides,the sandstones are characterized by high gammacerane index values varying in a broad range,whereas the shales and mudstones exhibit the opposite trend.Notably,the shales and mudstones generally have 8β(H)-drimane/8β(H)-homodrimane ratios exceeding 1,which,however,are typically less than 1 for the sandstones.A comprehensive analysis indicates that the variations in the distributions of the various hydrocarbon group components within the source rocks can be attributed to both differential adsorption and migration differentiation.