## 3 The Effect of Oil-Water Infiltration on the Component Structure of Cumulative Damage Rock  
To investigate the compositional and structural changes in damaged rock samples after different soaking times, EDS analysis and SEM observations were conducted using a ZEISS-sigma 300 instrument from Germany, with a magnification range of 10-200,000 times. Prior to testing, the rock samples were sprayed with gold. The EDS analysis was performed using a surface scanning method, and the results were expressed in atomic percentage. SEM observations were conducted at magnifications of 30 times and 100 times. Figure 4 presents the EDS analysis results of damaged rock samples after different soaking times. The rock samples mainly contain elements such as carbon, oxygen, aluminum, silicon, and potassium, with oxygen being the most abundant and potassium the least. As the oil-water soaking time increases, the content of these elements changes. Silicon, as a non-metallic element, is highly abundant in the Earth's crust. The variation in silicon content is a key indicator of rock structural changes. In nature, silicon primarily exists in the form of silicon oxides, which are widely present in various minerals. Silicon oxides influence structural characteristics by controlling mineral compositions. Since rocks contain multiple oxides, the variation in silicon content within silicon oxides was analyzed. Table 1 presents the compositional statistics of damaged rock samples after different soaking times, in which silicon content has a significant negative correlation with oil-water soaking time. As the soaking time increases, the silicon content decreases from 19.9% to 10.3%, representing a reduction of 48.2%. The decrease in silicon content indicates that with the increase of soaking time, the erosion degree of oil and water on the rock structure increases, the silicon oxide decreases, and the internal structure of the rock changes. Figure 5 presents SEM images of damaged rock samples after different soaking times. The surface of the dried damaged rock sample appears smooth, with distinct particle characteristics. However, due to the effects of loading and unloading, microcracks are present within the structure. After 8 h of soaking, the rock surface remains relatively smooth. Due to oil-water soaking, pits begin to appear on the surface, and the particle size significantly decreases, exhibiting a flocculent structure. This indicates that the hydrophilic substances within the sample interact with the oil-water mixture, initiating structural changes in the rock. After 16 h of soaking, microcracks and holes can be seen on the surface of the rock samples under a low magnification microscope, while deep cracks and block spalling appear under a high magnification microscope. After 24 h of soaking, the number and depth of holes on the surface of the rock sample increase further under the low magnification microscope. Under the high magnification microscope, holes left after the spalling of the block appear, more microcracks are distributed around the holes, and the characteristics of flocs below and on the right side of the holes are obvious. By integrating the EDS spectral analysis and SEM observations of damaged rock samples subjected to different soaking times, it can be concluded that oil-water soaking reduces the content of rock components and alters the internal rock structure. First, the oil-water mixture reacts with hydrophilic substances in the rock, modifying the surface morphology and facilitating subsequent surface block spalling. Then, the oil-water mixture decomposes silicon oxides in the rock, reducing silicon content and altering the internal rock structure. Ultimately, due to the combined effects of surface morphology changes and internal structural transformations, the rock undergoes block spalling, crack propagation, and an increase in pore development, leading to significant structural changes.