CO2 huff-n-puff technology has been acknowledged to enhanced oil recovery in tight oil reservoirs by improving oil mobility via CO2 dissolution. Temperature fluctuations induced on the reservoir depth have an impact on oil recovery by altering CO2 dissolution and oil mobility. A microscopic visualization simulation experiment was carried out under 2 MPa condition to observe the interactions between CO2 and crude oil at various temperatures (30, 45, 60, 75, and 90 °C). The contribution of viscosity reduction competition of temperature and CO2 dissolution to the improvement of crude oil mobility was thoroughly evaluated. The findings showed that CO2 dissolution dramatically lowers viscosity at 30–50 °C, facilitating oil mobility. Oil mobility and recovery are reduced by 8.2% as a result of CO2 dissolution decreasing with increasing temperature, while the volume of CO2 gas increases by 1.3 times. At 50–60 °C, the mobility of crude oil improves and the recovery increases significantly with the temperature, when the increment amplitude is about two times of the reduction in amplitude. Temperature-induced viscosity reduction predominates between 60 and 90 °C. Furthermore, the oil recovery is dominated by the matrix region at low temperatures (30–60 °C) and by the fracture region at high temperatures (75–90 °C), with both regions weighing more than 40% of the ultimate recovery. Therefore, CO2 huff-n-puff is more suitable at temperatures in the range of 50–60 °C in the extraction of tight oil reservoirs.

The water blocking phenomenon formed by the retention of fracturing fluid in the pores leads to an increase in the resistances of gas flow, thereby inhibiting the efficient extraction of coalbed methane (CBM) reservoirs. The opaque of the gas and water two-phase migration process and the ambiguity of its distribution characteristics jointly hinders the release of water blocking phenomenon. A visualization experiment for the gas–water two-phase displacement in the pores was implemented at ambient condition, while the porous media was divided into five flow regions based on the distribution characteristics of the seepage velocity field. The results showed there were “Y,” “I”, “L,” and “H” four primary types of water blocking phenomenon depending on the retention morphology of gas and water phases in different pores. The amount of “I” type water blocking phenomenon accounted for the majority in five regions, and the whole amount was five times than that of “H” type. The “Y” type water blocking phenomenon was created under the dual influence of pore radius and intersection angle, while the “I”, “L,” and “H” types manifest the corresponding morphology under the restriction of pore radius. The ratio of the amount of water blocking phenomenon in the main stream region to the upper and lower of transition region and boundary region exhibited a symmetrical distribution of approximately 3:2:1, mainly caused by the seepage velocity field induced by inhomogeneous pore structures. This research can provide a fundamental guidance for elimination of the water blocking damage in the extraction of CBM reservoirs.

This paper takes the gas cabin in the utility tunnel in the Xuwei District of Lianyungang as the study object. Based on the computational fluid dynamics (CFD) theory, a simulation model of the gas cabin in the utility tunnel is established. The propagation law of methane leakage and diffusion and the characteristics of methane explosion shock wave propagation were simulated under different conditions of the gas cabin. These conditions are the presence or absence, spacing and height of the air baffle. The results show that: (1) the gas baffle can limit the propagation of methane at the top of the gas cabin and slow down the velocity of diffusion so as to increase the concentration of methane near the baffle and speed up the time for the monitor to reach the alarm concentration; (2) the first peak pressure and the second peak pressure generated in the middle of the gas cabin are smaller than that when the gas baffle is installed. The gas baffle has the function of blocking the propagation of shock waves. However, due to the installation of the gas baffle, the superposition of the shock wave will make the pressure surge at the gas baffle; and (3) combined with the simulation results, it is recommended that the gas baffle spacing is not less than 50 m and the height setting is not greater than 0.5 m.

With the increase of mining depth, the deep mine waterproof wall project faces the test of worse construction environment and higher risk of water damage. With the development of intelligent construction technology, it is necessary to introduce concrete 3D printing technology for the construction of coal mine waterproof walls, so as to adapt to more complex construction environment and engineering needs. Through uniaxial compression tests, the compressive properties of 3D printed concrete were tested under different printing methods and force directions. The results showed that the compressive strength of the 3D printed concrete was higher under the conditions of printing path B and loading along the direction parallel to the bonding layer. According to test results, the mine waterproof wall structure based on concrete 3D printing was designed. Then, ABAQUS was used to simulate the compressive strength and deformation of the 3D printed waterproof wall. The results showed that the ultimate load of the 3D printing module was 6.697e⁴kN and the deformation range was controllable, which meet the engineering requirements. The advantages of 3D printing mine waterproof walls are more flexible in design, faster in manufacturing, and more intelligent in operation. This work provides new ideas for the design and construction of waterproof walls in deep mines.

Deep coal mining is seriously affected by a combined dynamic disaster of rock burst and coal and gas outburst, but the influence mechanism of gas on this combined dynamic disaster is still not very clear, which is significantly different from the single type disasters. In this study, to explore the effect of gas on the coal‐rock burst, a novel gas‐solid coupling loading apparatus is designed to realize gas adsorption of coal sample with burst proneness and provide uniaxial loading environment under different gas pressure. A series of uniaxial compression tests of gas‐containing coal with different gas pressure is carried out, and the energy dissipation process is monitored by an acoustic emission (AE) system. Results show that the macroscopic volume strain of the coal sample increases as gas adsorption and gas pressure increase under constant uniaxial loading pressure. Gas has the ability to expand the pores and natural fractures in coal sample by mechanical and physicochemical effects, which leads to a degradation in microstructure integrity of coal sample. With the increase of gas pressure, both the macrouniaxial compression strength (UCS) and elastic modulus show a downward trend; the UCS and elastic modulus of coal samples with 2 MPa gas pressure reduce by 58.78% and 48.82%, respectively, compared to those of the original coal samples. The main reason is that gas changes the pore‐fissure structure and the mesoscopic stress environment inside the coal sample. Owing to the gas, the accumulated elastic energy of the gas‐containing coal samples before failure reduces significantly, whereas the energy dissipated during loading increases, and the energy release process in the postpeak stage is smoother, indicating the participation of gas weakens the burst proneness of the coal sample. This study is of important scientific value for revealing the mechanism of combined dynamic disaster and the critical occurrence conditions of coal‐rock burst and coal and gas outburst.

In order to study the dynamic characteristics and microseismic distribution in the mining process of roadway with high gas and wide coal pillar, combined with the two dynamic events of N2105 working face in Yuwu Coal Industry, theoretical analysis and field measurement research were carried out. According to the theory of structural mechanics and geomechanics, the causes of dynamic appearance are analyzed. Combined with the specific situation, the influence of mining depth, coal pillar width, gas pressure, and content on the dynamic performance is analyzed. Stress monitoring and microseismic monitoring are carried out on one side of coal seam. The results show that, with the increase of the mining distance, the backside roof of the goaf is prone to unbalanced fracture due to the lack of lateral stress, and the impact pressure generated is used for the reserved protective coal pillar behind the goaf, causing the floor heave of coal seam. The combined stress generated by the anticlinal structure below the working face interacts with the abutment pressure of the working face to produce superposition effect, which promotes the occurrence of dynamic appearance. The critical depth of rock burst in Yuwu Coal Industry is about 600m. The increase of coal elastic energy caused by roof subsidence is more uniform with the increase of coal pillar width. The decrease of gas pressure in coal seam promotes the rock burst disaster. The vertical stress of coal seam at one side of the working face shows different evolution characteristics along the trend and strike. The vertical stress of coal seam in the lateral range of 53 m is adjusted to different degrees and tends to be stable until 300 m behind the working face. The active microseismic area in the middle of the working face was located 50 m in front of the working face, and the microseismic activity continued to 30–50 m behind the working face. The active microseismic area at the side of the roadway was located 30 m in front of the working face, and the microseismic activity continued to 100–180 m behind the working face. The inflection point, where the stress in the elastic area of coal pillar increases sharply, corresponds to the active microseismic area, which indicates that the dynamic characteristics in the mining process of roadway with high gas and wide coal pillar are related to the distribution law of microseismic. This study has a certain guiding significance for optimizing the width of reserved coal pillar, monitoring the coal seam stress/microseismic, and understanding the dynamic disaster of coal and rock under complex conditions.