微观剩余油赋存状态的矿物学机制探讨——以鄂尔多斯盆地中部中‒低渗砂岩储层为例

针对现阶段微观剩余油研究中可视化精度低、微观剩余油与矿物之间的依存关系不明确以及形态分类描述不完善等问题, 利用岩芯观察、铸体薄片分析、X射线衍射分析等手段, 以场发射环境扫描电子显微镜(FE-SEM)图像为基础资料, 联合能谱(EDS)分析资料, 研究鄂尔多斯盆地中部长2油层组和长9油层组的微观剩余油分布规律, 并探讨剩余油赋存状态的矿物学机制。结果表明, 微观剩余油的赋存状态由孔隙的大小和形态以及与孔隙相接触的边缘矿物的性质共同决定, 不同类型孔隙对剩余油的赋存能力取决于孔隙边缘矿物的形态、表面粗糙程度、比重和润湿性等物理化学性质。据此, 可将微观剩余油分为残留油团、半自由油岛、半自由油雾、半自由微油团和束缚油5个类型。

Mineralogical Mechanism of Micro-Remaining Oil Occurrence: An Example Study of Middle-Low Permeability Sandstone Reservoir of Ordos Basin

In order to figure out the existing problems of low visualization accuracy in the research of microresidual oil and clarify its morphological characteristics, this study discussed the distribution of residual oil occurrence state and its relationship with minerals. We conducted an integrated approach of core observation, casting film, X-ray diffraction (X-RD), field emission environmental scanning electron microscope (FE-SEM) and energy-dispersive spectrometry (EDS) analysis on middle-low permeability sandstone reservoir in the 9th member of Yanan Formation and 2nd member of Yanchang Formation from Ordos Basin, China. The result shows that different pore structure forms have different storage capacity for remaining oil, it depends on the properties of matrix minerals corresponding to the pore, including mineral morphology, surface roughness, specific gravity, wettability, etc, which can be classified into five types: residual oil block mess, semi-free oil blob, semi-free oil island, semi-free oil mist and irreducible oil.