Pore Structure Characteristics of Shale Oil Reservoirs with Different Lithofacies and Their Effects on Mobility of Movable Fluids: A Case Study of the Chang 7 Member in the Ordos Basin, China

被引:2
作者
Xiao, Yufang [1 ,2 ,3 ]
Ye, Zhengqin [4 ]
Wang, Hongliang [1 ,2 ,3 ]
Yang, Hailong [4 ]
Mu, Nana [1 ,2 ,3 ]
Ji, Xinyuan [5 ]
Zhao, He [1 ,2 ,3 ]
机构
[1] China Univ Geosci, Sch Energy Resources, Beijing 100083, Peoples R China
[2] China Univ Geosci Beijing, Key Lab Marine Reservoir Evolut & Hydrocarbon Acc, Minist Educ, Beijing 100083, Peoples R China
[3] China Univ Geosci, Beijing Key Lab Unconvent Nat Gas Geol Evaluat & D, Beijing 100083, Peoples R China
[4] Yanchang Oilfield Co Ltd, Yanan 716000, Peoples R China
[5] China Natl Offshore Oil Corp Ltd, Tianjin Branch, Tianjin 300459, Peoples R China
基金
中国国家自然科学基金;
关键词
pore size distribution; movable fluid distribution; Chang; 7; member; shale oil reservoirs; Ordos Basin; NUCLEAR-MAGNETIC-RESONANCE; TIGHT SANDSTONE RESERVOIRS; TRIASSIC YANCHANG FORMATION; THROAT STRUCTURE; PERMEABILITY; MINERALOGY; AREA; GAS;
D O I
10.3390/en17040862
中图分类号
TE [石油、天然气工业]; TK [能源与动力工程];
学科分类号
0807 ; 0820 ;
摘要
The Chang 7 member of the Triassic Yanchang Formation in the Ordos Basin is a significant continent shale oil reservoir in China. Therefore, conducting an in-depth investigation into the pore structure and fluid mobility characteristics of the Chang 7 shale oil reservoir holds immense importance for advancing shale oil exploration. This study conducts a detailed analysis of the pore structures and their impact on fluid mobility of the Chang 7 shale oil reservoir using multiple methodologies, i.e., a cast thin section, scanning electron microscopy (SEM), X-ray diffraction (XRD), high-pressure mercury injection (HPMI), low-temperature nitrogen adsorption (LTNA), and nuclear magnetic resonance (NMR). The results show that the sandstone in the Yanwumao area of the Chang 7 shale oil reservoir consists mainly of lithic arkose and feldspathic litharenite, which can be classified into three lithofacies (massive fine-grained sandstone (Sfm), silt-fine sandstone with graded bedding (Sfgb), and silt-fine sandstone with parallel bedding (Sfp)). Moreover, three pore structures (Type I, II, and III), and four pore spaces (nanopores, micropores, mesopores, and macropores) can be characterized. Pore structure Type I, characterized by large pores, exhibits bimodal pore diameter curves, resulting in the highest levels of movable fluid saturation (MFS) and movable fluid porosity (MFP). Pore structure Type II demonstrates unimodal pore structures, indicating robust connectivity, and higher MFS and MFP. Pore structure Type III primarily consists of dissolved and intercrystalline pores with smaller pore radii, a weaker pore configuration relationship, and the least fluid mobility. Furthermore, a correlation analysis suggests that the pore structure significantly impacts the fluid flowability in the reservoir. Favorable petrophysical properties and large pores enhance fluid flowability. Micropores and mesopores with high fractal dimensions have a greater impact on reservoir fluid mobility compared to macropores and nanopores. Mesopores mainly control MFS and MFP, while micropores govern the shift from bound fluid to movable fluid states. Among the lithofacies types, the Sfm lithofacies exhibit the highest fluid mobility due to their significant proportion of macropores and mesopores, whereas the Sfgb lithofacies have lower values because they contain an abundance of micropores. The Sfp lithofacies also dominate macropores and mesopores, resulting in medium fluid mobility levels. This study combines lithofacies types, micro-reservoir pore structure characteristics, and mobile fluid occurrence characteristics to better understand the dominant reservoir distribution characteristics of the Chang 7 shale oil reservoirs in the Ordos Basin and provide theoretical information for further optimization of production strategies.
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页数:20
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