东濮凹陷西斜坡盐湖相原油地球化学特征与油源分析

Characteristics and Formation Mechanisms for the Saline Lacustrine Oil in the West Slope of the Dongpu Sag

东濮凹陷西斜坡油气成因与成藏机理复杂。采用色谱-质谱、傅立叶变换离子回旋共振质谱(ESI FT-ICR MS)、单体烃碳同位素等地球化学方法对东濮凹陷西斜坡原油特征及成因进行了剖析。共分出两种成因类型原油,第Ⅰ类为马寨地区原油,具有较低Pr/Ph(均值0. 39)和C29-/C30-藿烷(均值0. 33)、较高C35-/C34-藿烷(均值1. 56)和二苯并噻吩/菲值(均值0. 27)等强还原性、盐湖相原油特征,主要来自马寨次洼沙三下—沙四上亚段烃源岩;第Ⅱ类为胡庆-邢庄地区原油,盐湖相特征不及第Ⅰ类,主要来自柳屯、海通集洼陷埋深> 3 000 m的沙三下—沙四上亚段烃源岩。ESI-FT ICR MS检测到深部原油含有热稳定性较低的硫化物,其硫同位素也偏高,指示TSR对深部油气的改造作用。观察到西斜坡地区烃源岩具有明显不同的两种热演化趋势,反映膏盐岩对烃源岩生烃演化显著的控制作用。西斜坡已发现原油大多具有低熟、早期成藏特征,与海通集、柳屯洼陷深部较高热演化程度烃源岩较为发育不太匹配,指示研究区具有潜在的深部油气勘探前景。

The hydrocarbons generation and migration style in the West Slope of the Dongpu Sag is rather com plex.Geochemical methods including GC//MS,ESI FT-I(]R MS and isotopic analysis,combined with geological methods are used to reveal hydrocarbon characteristics and genetic mechanisms for the saline lacustrine oils.The crude oils analyzed were subdivided into two oil families.Oil family-I is these oils in the Mazhai Tectonic Belt,which were charactered by relatively low ratios of Pr/Ph(mean 0.39)and C29-/C30_hopane(mean 0.33),and relatively high ratios of C35-/C34_hopane(mean 1 56)as well as dibenzothiophene/phenanthrene(mean 0.27).This family was primarily derived from the E53L-E54U mudstones/shales deposited under strong reduction and saline-water paleoenvironment in the Mazhai Sag.Oil family-II isthoseoilsintheHuqing-Xing-zhuang area,featured by characteristics of a little different from the family-I,which has a relatively low^ratio of C35-/C34-hopane and dibenzothiophene/phenanthrene relative to the oil family-I.The oils of family-II are primarily derived from the E53L-E54U mudstones/shales in the Huqing Tectonic Belt and the adjacent Haitongqi Subsag with a burial depth>3,000 m according to oil-source rock correlation.It is the precursors and paleoenvironment which caused the differences betw^een the oils.Abundant sulfur compounds with relatively low thermal stability were detected in the deep oils analyzed by ESI FT-ICR MS,accompanied by relatively high sulfur isotope of individual sulfur compounds.Both of the phenomenon suggest thermochemical sulfate reduction(TSR)experienced by the oils.Two thermal evolution trends were observed for the source rocks in the area suggesting affection of thick gypsum-salt rocks on the hydrocarbons generation of the source rocks.Most of the crude oils in the Huqing area are less mature,which is not coincided with the considerable amounts of deep source rocks developed in the area,suggesting a good potential of deep tight oil-gas exploration and exploitation in the area.