松辽盆地北部青一段泥页岩储集特征及孔隙演化

松辽盆地青一段是泥页岩油勘探重点层段。利用泥页岩物性分析、氩离子抛光和场发射电镜观察探讨该套泥页岩物性特征及孔隙类型,根据成熟度演化、生烃转化、有机酸含量与孔隙度的变化关系分析了泥页岩孔隙演化特征。研究结果表明:青一段泥页岩孔隙度较高、渗透率很低,总孔隙度平均为7. 94%,基质渗透率平均为1. 16×10^-8μm^2;孔隙类型有粒间孔、晶间孔、有机质孔、溶蚀孔和微裂缝;有机质孔为藻类生烃后残留孔隙,孔隙呈长条形和不规则形状,直径多为20～400 nm,有机质孔形成于Ro为0. 7%以后,大量形成对应的Ro为0. 9%～1. 2%,在Ro为1. 2%时孔隙度达2. 7%;当埋深小于2 000 m时青一段泥页岩孔隙度随埋深增加而减小,当埋深大于2 000 m时孔隙度出现2个异常峰值,孔隙度的增大主要因为有机酸溶蚀和藻类生烃作用;根据孔隙度与埋深关系,预测了齐家—古龙凹陷为泥页岩油有利勘探区。研究成果可为松辽盆地泥页岩油勘探和评价提供依据。

Accumulating characteristics and pore evolution for Member Qing-1 mud shale in North Songliao Basin

Qing-1 Member( K2qn1) is the key target of the mud-shale-oil exploration in northern Songliao Basin,Northeast China. With the help of the analyses of the physical properties,argon iron beam milling and the field-emission SEM observation,the physical property characteristics and pore types were explored for the mud shale. According to the relationships between the maturity evolution,hydrocarbon generation,organic acid content and the porosity,the evolution properties of the mud shale were analyzed. The study results show that K2qn1 mud shale is characterized by higher porosity and rather lower permeability,the total porosity is at 7. 94% averagely,the average matrix permeability is at 1. 16×10-8μm2;the pore types include inter-particle pore,inter-crystalline pore,organic pore,dissolved pore and micro-fractures;the organic pore is resulted from the freed space after the hydrocarbon generation of alginite,the pore is in the form of elongated stripe and irregular shape,the diameters are mainly in the range of 20-400 nm,the organic-matter pores are formed at Rogreater than 0. 7% and the vast organic-matterpores are generated at Roin the range of 0. 9%-1. 2%,when the Rois 1. 2%,the porosity is up to 2. 7%. At depth above 2 000 m,the porosity in K2qn1 mud shale decreases with the increase of depth,whereas at depth below2 000 m,two abnormal peak values appear for the porosity;the main reasons for the porosity increase are organic acid dissolution and hydrocarbon generation from alginite. According to the relationship between porosity and depth,the favorable exploration region was predicted for the mud shale oil in Qijia-Gulong Sag. The study results can support the shale oil exploration and assessment in Songliao Basin.