## 1 Introduction  
Coal and oil resources co-storage areas are predominant in Songliao, Junggar, Tarim, Qaidam, and Ordos Basins in China [1, 2]. The Shuangma coal mine in eastern Ningxia is in the coal and oil resources co-storage area in the Ordos Basin (Figure 1). The coal mine contains numerous abandoned oil wells that were left over from early oil exploration and connect the coal seam and the oil-bearing layer. After over 60 years of precipitation, the gas in the oil-bearing layer accumulates in the oil well cavity and generates a high pressure. The pressure provides continuous power for the oil and gas and promotes their diffusion into the coal mass fracture, forming an oil-gas accumulation area around abandoned oil wells [3]. During oil and gas enrichment, the initiation, propagation, coalescence, expansion failure, and rapid release of accumulated coal mass fracture stress [4] can induce dynamic disasters, such as coal mass instability/collapse and oil-gas diffusion. The essence of dynamic disaster in the co-storage area of coal and oil resources is the failure mechanism of coal and rock mass. Therefore, the fundamental studies on the dynamic evolution characteristics of coal mass fractures in coal and oil resources co-storage areas are vital to warning against dynamic disasters. Recently, several novel technologies have been employed to investigate the micro-structure and fracture characteristics of coal rock. Computed tomography (CT) scanning is a non-destructive testing method [5], which is suitable for rapidly acquiring the internal structural characteristics of rocks. CT has scanning, imaging, and visualization functions and does not deform samples [6, 7]. [PERSON] [8] used X-ray CT imaging and digital imaging techniques to study the anisotropic damages and spatial fracture evolution of sandstone under uniaxial compression. Likewise, [PERSON] [9] used CT scanning to analyze the fracture propagation of sandstone subjected to loading. [PERSON] [10] performed CT scanning on failed rock samples to investigate the fracture evolution law. However, because of the resolution constraint of CT devices, CT images can only be used for describing the evolution law of macro-fractures. Therefore, the effect of micro-fractures on coal mass damages can be investigated using the average CT number method [11, 12, 13]. The evolution characteristics of rock fracture can be monitored using acoustic emission (AE) signals, which depict how the dynamic disaster develops in coal and rock mass. [PERSON] [14] used collision parameters to describe the dynamic process from microcrack nucleation to macro-fracture formation. [PERSON] [15] analyzed the failure of granite under uniaxial compression by observing the changing AE energy. [PERSON] [16] also investigated the frequency spectrum characteristics of coal mass during fracturing induced by uniaxial compression. [PERSON] [17] examined the AE and electromagnetic radiation laws during the deformation and failure of coal mass. [PERSON] [18] adopted parameters such as AE counts and dominant frequency to describe the propagation of a prefabricated fracture of coal mass under compression. [PERSON] [19] categorized AE incidents into tensile and shear fracture incidents according to different wave characteristics, using the RA-AF (rise time/peak amplitude-count/duration) relation. [PERSON] [20] found that granite had an increased RA after subsequent disturbance-induced failures when loading exceeded 60% of the compression strength. Studies on AE signals provide important data for the characteristic evolution analysis of coal mass instability and disaster warning [21, 22, 23]. Previous studies on coal mass damages mainly focused on the impact of fracture structure on the strength and anisotropic characteristics of coal and rock mass under uniaxial compression. Few studies have investigated the RA-AF fracture evolution characteristics  
Figure 1: Oil and gas disasters in coal and oil resources co-storage areas.