海陆交互相与陆相页岩储层差异性特征:以鄂尔多斯盆地东北部临兴-神府工区山西组为例

Characteristics of reservoir variability of transitional and continental shale,Shanxi Formation, Linxing and Shenfu area,Northeastern Ordos Basin

海陆过渡相页岩和陆相页岩所处的沉积环境较为复杂,非均质性强,目前未形成统一性认识,对2类页岩的储层发育特征及其影响因素的研究尚显薄弱。为此,选取鄂尔多斯盆地东北部临兴-神府地区山西组页岩为研究对象,对比分析海陆交互相和陆相页岩的储层特征,以研究不同沉积环境下页岩的储层差异性及影响孔隙发育的因素。首先,通过总有机碳w(TOC)、镜质体反射率Ro和岩石矿物组分分析实验,分别说明2种沉积环境页岩的有机质特征和矿物质量分数;其次,结合氩离子抛光-扫描电镜,直观地观察页岩孔隙的形态特征;最后,通过高压压汞、氮气吸附/脱附和二氧化碳吸附实验,定量表征页岩孔隙发育特征。研究结果表明:陆相页岩的w(TOC)均值为2.62%,Ro均值为1.03%,w(石英)均值为55.31%,总孔隙体积均值为0.010 6 cm3/g,以发育无机孔为主,可见微米级有机质孔;海陆交互相页岩的w(TOC)均值为1.49%,Ro均值为1.04%,w(石英)均值为45.57%,总孔隙体积均值为0.009 4 cm3/g,多发育无机孔和与有机质相关的微裂缝。相比海陆过渡相页岩,陆相页岩的储层发育特征较优,且w(TOC)与2种沉积环境的页岩孔隙体积均呈现弱负相关性,而由于不同沉积环境的黏土矿物成分的差异性,导致w(黏土矿物)与海陆交互相页岩的孔隙体积呈反比,而与陆相页岩孔隙体积呈正比。

Due to the unstable sedimentary environment and strong heterogeneity, there is no unified understanding of continental shale and transitional shale. The characteristics of reservoir and influencing factors of these two types of shale are still unclear. Therefore, the shale of Shanxi formation in Linxing and Shenfu area in the northeast of Ordos Basin were selected as the research objects to conduct comparative analysis on the reservoir characteristics of transitional and continental shale respectively. The aim is to explain the reservoir development characteristics, differences and main controlling factors of pore development of shale in the two sedimentary environments. Firstly, the organic matter characteristics and brittle mineral mass fraction of shale in two sedimentary environments were respectively illustrated by the analysis of total organic carbon w(TOC), vitrinite reflectance Roand rock mineral composition. Secondly, the morphological characteristics of shale pores were observed visually by Ar-SEM(argon ion polishing scanning electron microscopy). Thirdly, the shale reservoirs were quantitatively analyzed by high-pressure mercury injection, nitrogen adsorption/desorption and carbon dioxide adsorption/desorption experiments, aiming to describe the characteristics of shale pores development at multiple scales from quantitative aspects. For continental shale, the mean w(TOC) is 2.62%, the mean Rois 1.03%,and the mean w(quartz) is 55.31%. The mean total pore volume of continental shale is 0.010 6 cm3/g, mainly inorganic pores, and micron-scale organic matter pores can be seen. For transitional shale, the mean w(TOC) is1.49%, the mean Rois 1.04%, the mean w(quartz) is 45.57%, the mean total pore volume of transitional shale is0.009 4 cm3/g, and inorganic pores and organic-related micro-fractures mostly develop. The above experimental analysis shows that the reservoir development characteristics of continental shale are better than that of transitional shale, and w(TOC) has a weak negative correlation with the pore volume of continental and transitional shale. In addition, due to the differences in the composition of clay minerals in different sedimentary environments, the pore volume of w(clay minerals) is inversely proportional to that of transitional shale, and positively proportional to that of continental shale.