###### Abstract  
The evaluation of pore characteristics in lacustrine shales is of significance for shale oil and gas exploration in terrestrial sedimentary basins. However, due to the complex depositional environments, there have been few reports on the quantitative evaluation of lacustrine pores. In this study, we carry out experiments, e.g., scanning electron microscopy (SEM), nitrogen adsorption, X-ray diffraction (XRD), and rock pyrolysis, on sixteen lacustrine shale core samples of the Late Cretaceous Nonjiang Formation (K\({}_{2}\)n\({}^{1+2}\)) in the Songliao Basin. At the same time, we bring in the fractal dimensions to quantitatively characterize the pores of shale samples in K\({}_{2}\)n\({}^{1+2}\). The kerogen type of shales in the Nenjiang Formation is mainly type I. The shales of K\({}_{2}\)n\({}^{1+2}\) develop a large number of mineral intergranular pores and a small number of organic pores and mineral intergranular pores. The primary minerals of the samples are clay minerals and quartz. The total organic carbon (TOC) has a correlation with the pore physical parameters, whereas the content of minerals does not correlate significantly with pore development. The average pore fractal dimensions obtained from the analysis of nitrogen adsorption data are D1 = 2.5308 and D2 = 2.6557. There is a significant negative correlation between the fractal dimensions (D1 and D2) and the TOC content: the lower the fractal dimensions, the higher the TOC, and the more the free oil. In low maturity shales with higher TOC content, due to hydrocarbon generation, larger pores with a regular shape (small fractal parameters) can be produced, which can store more free oil. The shale reservoir evaluation of K\({}_{2}\)n\({}^{1+2}\) in the Songliao Basin should be focused on shales with higher TOC and lower pore fractal parameters. Our work provides a reference for the shale oil evaluation of K\({}_{2}\)n\({}^{1+2}\) in the Songliao Basin and complements studies on lacustrine pore characteristics. s 202  
the pore systems of lacustrine shales are less known due to more complex depositional environments and lithofacies in lacustrine shales, which may cause different pore structure characteristics and different influences on shale oil/gas enrichment and production. Therefore, the quantitative evaluation of lacustrine pores is significant but has been seldom reported [18; 19; 20; 21; 22]. Shale contains a large number of nano-micron pores and has a very strong heterogeneity. The traditional technical methods for pore structure studies have limitations and cannot effectively describe the pore structure and surface morphology. In this regard, the characterization of shale pore structure requires a multi-technology, multi-scale, and multi-faceted method [2; 3; 3; 8; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32]. [PERSON] proposed the fractal geometry theory to characterize the special structure of many objects with complex shapes in nature; the geometry of shale pores is a typical example of such shapes [33; 34; 35]. [PERSON] et al. were the first to demonstrate the fractal characteristics of reservoir pores by molecular adsorption [36]. [PERSON] et al. used SEM to observe rock samples and found that pores in the range of 0.2 to 5.0 in sandstones, shales, and carbonates have good fractal properties [35]. [PERSON] and [PERSON] also supported the theory by confirming the fractal characteristics of several sandstones [37]. With the research on the pore structures of shale, fractal theory has become an effective method to characterize the complexity of pore structures in shale [38; 39; 40]. The Songliao Basin in northeast China is a large Cretaceous terrestrial basin and a petroleum-bearing sedimentary basin [41; 42; 43; 44; 45]. There are two sets of shales as source rocks and shale oil reservoirs: the Qingshankou Formation (K\({}_{2}\)q) and the Nenjiang Formation (K\({}_{2}\)n) [42; 44; 46; 47].