## 3 Samples and Test Methods
### Experimental Methods  
An organic petrographic study was conducted in the Key Laboratory of Oil Shale and Coexistent Energy Minerals of Jilin Province. For the production of light sheets for the organic petrographic study, a small rock sample (20 \(\times\) 20 \(\times\) 10 mm) was first installed in a hardening agent mixture, and the polyester resin was allowed to slowly set. After preliminary treatment, the samples were polished with a diamond grinding plate, silicon carbide paper and alumina powder. The petrographic examination used a high-power optical microscope (China) equipped with a photometry system with a fluorescent lamp. Mean random vitrinite reflectance measurements (%, Ro) and organic maceral observations were conducted on 24 samples following ASTM Standard D7708-14 (2014). Using a Philip-PW 1830/40-CuK\(\alpha\) radiation device (Philips, Japan) (1.54 A, 35 kV and 35 mA), the collected mineral data were qualitatively and quantitatively processed by X-ray diffraction (XRD) analysis at the Center for Scientific Test of Jilin University (China). The rock samples were crushed into 200 mesh powder, the carbonate in the sample was removed with excessive dilute hydrochloric acid and the carbonate content was calculated. The total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS) contents of all samples were determined by a vario PYRO cube element analyzer (Elementar, UK) and calculated according to the carbonate content at the Key Laboratory of Oil Shale and Coexistent Energy Minerals of Jilin Province following standard GBT-19145-2003. The instrument used in the rock pyrolysis experiment analysis was a Rock Eval-6 analyzer (French Petroleum Research Institute) at the Center for Scientific Test of Jilin University (China). The parameters S1, S2, S3 and T\({}_{\rm max}\) were measured, and the hydrogen index (HI), oxygen index (OI) and production index (PI) were calculated accordingly. In these methods, the amount of pyroylate released from kerogen was normalized to TOC to give the HI. The temperature of maximum hydrocarbon generation (T\({}_{\rm max}\)) is defined at the maximum value of the S2 peak and serves as a maturity indicator. For the organic geochemical analysis, thirty-eight selected samples were extracted using a Soxhlet apparatus (China) with a mixture of dichloromethane and methanol (93:7). Elemental sulfur was removed by the addition of activated copper turnings. Asphaltenes were precipitated from a hexane-dichloromethane solution (80:1) and separated by centrifugation. The extracted organic matter was separated into saturated hydrocarbons, aromatic hydrocarbons and nitrogen, sulfur or oxygen (NSO) compounds by liquid chromatography. At the Key Laboratory of Oil Shale and Coexistent Energy Minerals of Jilin Province, the saturated components were dissolved in petroleum ether and analyzed by Agilent gas chromatography-mass spectrometry (Agilent Technologies Inc. USA) with an HP-5 MS elastic quartz capillary (60 m \(\times\) 0.25 mm \(\times\) 0.25 mm) GC column. The temperature ranged from 40 to 300 \({}^{\circ}\)C at a rate of 4 \({}^{\circ}\)C/min and was then held for 30 min at 300 \({}^{\circ}\)C. The hydrocarbon fractions were subsequently analyzed by an Agilent 5975B inert MSD mass spectrometer (Agilent Technologies Inc. USA) with a gas chromatograph attacheddirectly to the ion source (70 eV ionization voltage, 100 mA filament emission current, 230 \({}^{\circ}\)C interface temperature). Compound separation was performed on a column similar to the GC column. The saturated hydrocarbon ratios and the relative abundance of steranes and triterpenes were calculated from the integrated peak areas of the relevant ion chromatograms m/z 191 and m/z 217. The aromatic hydrocarbon ratios were also calculated from the integrated peak areas of the relevant ion chromatograms following standard GBT-30431-2013. In the process of drilling, the abnormal presence of natural gas was detected by gas logging.