碎屑储集岩热磁特征与磁性矿物识别

Thermomagnetic Properties of Clastic Reservoir Rocks and Identification of Magnetic Minerals

对采自渤海湾盆地济阳坳陷孤南洼陷4口探井的22块古近系沙河街组碎屑储集岩标本进行了细致的磁化率-温度曲线、三轴饱和等温剩磁热退磁测试,研究不同含油级别的储集岩的热磁特征与磁性载体,结果表明:孤南洼陷沙河街组储集岩磁性矿物及其组合可以划分为3种类型:磁铁矿、针铁矿+磁黄铁矿+磁铁矿、赤铁矿+磁铁矿,岩石的磁性载体及其组合与岩石的颜色、岩性等沉积学特征密切相关,而与含油性关系不明显;在氩气环境中加热,含油标本中的磁铁矿Hopkinson峰低而宽,甚至不明显,居里温度附近曲线多呈锯齿状,冷却过程中,磁铁矿重现作用不明显,烃类有机质对碎屑储集岩中沉积成因磁铁矿的热磁行为具有一定的控制作用;烃类流体侵位,储集岩中的磁性矿物及其组合未发生明显变化,亦不存在某种演化序列或规律性,烃类流体化学重磁化不具普遍性。

A total of 22 specimens for thermomagnetic analysis and identification of magnetic minerals were collected from the Cenozoic clastic reservoir rocks in Gunan Sag in the Bohaiwan Basin. Magnetic minerals and their assemblages in clastic reservoir rock specimens can be divided into three types: magnetite, goethite-pyrrhotite-magnetite, hematite-magnetite. Magnetic carriers in the rocks are closely related to lithology and have no obvious correlation with hydrocarbon saturation. Hydrocarbons have a certain influence upon thermomagnetic behavior of sedimentary magnetite in the clastic rocks. Heated in an argon environment, the Hopkinson peak of magnetite in the oily specimens is low and wide. In the cooling curve, the reappearance of magnetite is not obvious. The hydrocarbon emplacement, magnetic minerals and their assemblages in clastic reservoir rocks do not significantly change. Authigenic magnetite related to hydrocarbon fluids migration and accumulation is not widespread in the oily reservoir rocks.