Geological characteristics, evaluation criteria and discovery significance of Paleogene Yingxiongling shale oil in Qaidam Basin, NW China

LI Guoxin,ZHU Rukai,ZHANG Yongshu,CHEN Yan,CUI Jingwei,JIANG Yinghai,WU Kunyu,SHENG Jun,XIAN Chenggang,LIU He

Table 2 Comparison of geological characteristics between Yingxiongling area in Qaidam Basin and typical shale oil areas in China

Typical basin Typical zones Shale oil stratum Burial depth/m Sedimentation Source rock Shale oil type Reservoir Pressure coefficient Fluid property Structural background Waterbody property Thickness/m Organic matter type TOC/% S1/(mg·g-1) Ro/% Lithology type Thickness of sweet spot/m Reservoir space Porosity/% Permeability/ 10-3 μm2 Throat diameter/nm Brittle mineral content/% Crude oil density/ (g·cm-3) Gas-oil ratio/ (m3·m-3) Oil saturation/% Junger Jimsar sag Permian Lucaogou Formation 2300-4300 Foreland basin Salted lake basin 200-1250 I—II 1.0-16.0 1.0-12.0 0.5-1.8 Interlayer, mixed accumulation, shale Laminated diamictite with tuffaceous, sandy interlayer 4-33 Micron-scale dissolution pores, nano-scale intercrystalline pores, and laminar fractures 5.50-19.94 0.000 4-1.950 0 200-400 60-90 1.2-1.5 0.89-0.93 10-20 80-90 Erdos Qingcheng area Triassic Yanchang Formation, Chang 7 Member 1600-2200 Depression basin Freshwater lake basin 10-160 I—II 0.8-22.0 (Mainly 3.0) 1.0-10.0 0.6-1.0 Interlayer, shale Felsic shale with gravity flow sandstone interlayer 2-26 Micron-scale dissolution pores, nano-scale intercrystalline pores, and foliation fractures 6.00-12.00 0.03-0.50 40-180 40-90 0.7-0.8 0.83-0.88 20-100 60-80 Songliao Gulong sag Cretaceous Qingshankou Formation 1600-2500 Depression basin Fresh water lake basin, locally semi- saline lake basin by sea transgression 50-600 Mainly Type I 0.5-5.4 (Mainly 2.0) 1.5-20.0 0.4-1.3 Interlayer, shale Felsic shale silty fine sandstone interlayer 10-22 Micron-scale dissolution pores, nano-scale intercrystalline pores, and foliation fractures 3.40-16.00 0.01-1.00 20-200 40-60 1.2-1.6 0.78-0.87 50-500 >50 Bohai Bay Qikou, Cangdong sag Paleogene Kongdian and Shahejie Formation 2600-4200 Faulted basin Salted lake basin 400-1200 I—II 0.5-26.0 2.0-8.0 0.3-1.8 Interlayer, mixed accumulation, shale Felsic and calcareous shale with siltstone mixed carbonate 10-40 Micron-scale dissolution pores, nano-scale intercrystalline pores, and laminar fractures 3.00-12.00 0.03-12.00 30-550 50-70 1.2-1.9 0.86-0.89 50-130 20-80 Qaidam Yingxiongling area Upper member of Lower Ganchaigou Formation of Paleogene 2500-5500 Compressional basin Salted lake basin 1000-1500 I—II 0.6-2.7 1.0-40.0 0.6-1.3 Mixed accumulation, shale Laminated shale and limy dolomitic shale 2-20 Micron-scale dissolution pores, nano-scale intercrystalline pores, and laminar fractures 3.10-11.50 0.05-0.62 20-400 50-80 1.7-2.5 0.78-0.85 40-300 40-88