江汉盆地马王庙油田自生磁铁矿与烃运移相互关系研究

研究表明，已知油井M36井Ⅱ油组的含油层（位于Ⅱ油组的中—下部）中有明显呈规律分布的强磁性层。以平均值为例，含油岩层屑的饱和磁化强度Js=352.58A/m，饱和剩磁Jc=60.43A/m；而干层的Js=147.34A/m，Jr=22.09A/m。磁滞回线特征表明，含油层岩屑中以偏软的磁性矿物为主（平均矫顽力Hc=33.5mT，饱和磁场Hs=0.25T），而干层岩屑中主要为磁性偏碱的磁性矿物（Hc=44.2mT，H8=0.4T）。重矿物分析结果显示，干井M46井Ⅱ油组岩屑中含沙射影有较多的碎屑磁铁矿。磁学与矿物学参量的对应分析表明，含油层强磁性岩层的载体为自生成因的磁铁矿，而菱铁矿与黄铁矿为非磁性矿物，对Ⅱ油组岩层的磁性没有影响。由此，我们提出M36井含油层中的自生磁铁矿可能是原油的生物降解作用、碎屑矿物中高价铁的被置换及后期菱铁矿的氧化作用等多种不同时空条件下形成的产物。

A Study of the Relationship between Authigenic Magnetite and Hydrocarbon Migration in Mawangmiao Oil Field From Jianghan Basin

Magnetic and mineralogic parameters of well cuttings of II You Formation (Oil-bearing layer in this Region),Paleogene Xingouzi Group from well M36(Oil well)and M46 well (dry well)(two wells situated in Mawangmiao nose structure) are systematicaly mea-sured, in order to evalute secondary alternation associated with hydrocarbon mingration, according s magnetic and mineralogic parameters variation characteristics of well cuttings. Results show that there are strong magnetic layers within II You Formation from well M36 and average values of saturation magnetization Js and saturation istohermal remanent Jr are 352.58A/m, and 60.43A/m, and then well M46 are 147.37A/m and 22.09A/m, respectively. The characteristics of magnetic hysteresis loops indicate that predominant soft magnetic minerals occur within samples of oil-bearling layers (intrinsic coercivity Hc=33.5mT, saturatio magnetic field Hs=0.25T), but are dominantly hard magnetic min-erals in dry layers (Hc=44.2T, Hs=0.4T).The results of heavy mineral analysis indi-cate that well cuttings in well M46 contain abundant detrital magnetite. The results of in-tegrated magnetic with mineralogic analysis show that magnetic carriers within samples with strong magnetism is arthigenicmagnetite, and then siderite and pyrite are non-mag-netic minerals and can not contribute to magnetism of II You Formation in well M36. So, we infer that authigenic magnetite within oil-bearing samples of well M36 may be products due to crude oil biogradation, replacement of ferric-iron in detrital magnetic minerals by ferrous iron under reduction environment and oxidation of siderite in the late stage. These results support intensively reliable genetic correlation between hydrocarbon mingration and the precipitation of authigenic magnetic minerals, and provide important evindences for di-rect location technologies (LDT) oil/gas reservoirs.