## 1 Introduction
To get a full picture of the changes before and after the thermal exposure during the combustion test, it is necessary to provide a detailed laboratory analysis of the core samples [9, 22]. In the physical modeling of the combustion process, the tube is typically filled with unconsolidated core or core chips. However, the use of the crushed core pack is beside the purpose as the shale is characterized by low porosity and permeability. It is complicated to evaluate the saturation of the rock and kerogen conversion in the crushed samples caused by physical and chemical changes. First, one of the tasks of the current study was to investigate and analyze the petrophysical and geochemical rock properties caused by front propagation and oil displacement in organic-rich consolidated core samples (standard cylinders). The second was to select and check the viability of advanced laboratory techniques to control and to evaluate these changes. One of the conventional methods for determining reservoir properties is standard pressure pulse-decay permeatory [23]. The investigation of reservoir properties of shale samples requires new or modified methodologies in comparison with ones adopted for the study of conventional reservoir rocks [24, 25]. The reason is the low porosity and permeability values, the high content of organic matter (mainly solid) insoluble in organic solvents phase (kerogen), and the presence of high-carbon bitumen. Among the recent technologies used in studies of unconventional reservoirs, attention is paid to the identification of the fluids based on NMR relaxometry [26]. Low-field NMR relaxometry is often used as a non-destructive tool for determining the saturation and pore space structure of the low-porosity organic-rich rock [26; 27; 28]. Therefore, the main potential of kerogen-containing rocks is associated with the volume of hydrocarbons that can be generated from a unit volume of rock. In addition to the reservoir properties and liquid saturation, it is important to characterize the OM properties by Rock-Eval pyrolysis. There are several ways to investigate the micromorphology of the samples [29; 30]. Atomic force microscopy (AFM) allows for a detailed investigation of the sample surface with the calculation of morphological parameters [30]. Scanning electron microscopy (SEM) is widely used for the evaluation of rock texture and microstructure with secondary electron and backscattered electron detection in shales [29]. SEM was chosen as the method for studying the pores of nanometer size. The integration of the set of experimental techniques (gas permeametry, NMR, Rock-Eval pyrolysis, and SEM) allowed us to investigate the dynamics of changes in the physicochemical state of rock samples before and after exposure  
In our previous papers, we presented the results of thermal exposure to source rock and the results of experimental and numerical simulation of thermal EOR on an example of the local shale Bazhenov Formation (BF) [31; 32; 33]. The Bazhenov Formation is one of the most prominent shale formations in the world, and it is characterized by a complex lithological structure, a high quantity of viscous components, and heterogeneity of the rock [34]. That is why thermal enhanced oil recovery techniques should be developed to unlock the oil shale potential [35]. The results of laboratory modeling of various thermal recovery methods for the Bazhenov Formation are presented in many publications [31; 36; 37]. In this study, we analyze the influence of thermal and oxidation exposure on petrophysical (porosity, permeability, saturation) and geochemical properties (OM quality) on the case of Bazhenov Formation rock samples. All the studies are conducted on standard-sized core plugs located inside the combustion tube.