Coal Pore Research Articles

Influence of active water on gas sorption and pore structure of coal

Active water fracturing is one of the commonly used technologies in area for enhanced coalbed methane (CBM) extraction. However, after the fracturing process, active water residues may block the pore of coal and ultimately reduce the production of CBM. To address this limitation, pore structures of Dongtan (DT) and Houwenjialiang (HW) coal samples were subjected to active water fracturing effect using active water with different concentrations of PAM prepared using polyacrylamide (PAM). Methane adsorption experiment was conducted to probe the effect of active water on the adsorption of methane in coal samples. Additionally, low-temperature nitrogen-adsorption experiments (LT-NAT) and nuclear magnetic resonance (NMR) were probed to characterize the discrepancies in the pore structure and chemical composition surface functional groups of the two coal-sample types. The results showed that considerable discrepancies existed in the pore structures of the two coal-sample types; however, their surface functional groups were similar. The active water treatment had contrasting effects on the adsorption behavior of methane features of the two coal-sample types, that is, as concentration of PAM in the active water increased, the methane adsorption of the treated HW coal sample increased whereas that of the treated DT coal sample gradually decreased. The PAM molecules in the active water residue could adsorb methane, and blockage of pores by the residue will reduce the amount of methane adsorption. The combined effect of the two dominated the influence of active water fracturing on methane sorption. Further optimizing the active water formulation to improve the flowback effect can be a very useful channel of reducing damage to the coal seam.

Effects of Pore Structure of Different Rank Coals on Methane Adsorption Heat

Adsorption thermodynamic characteristics are an important part of the methane adsorption mechanism, and are useful for understanding the energy transmission mechanism of coalbed methane (CBM) migration in coal reservoirs. To study the effect of coal pore characteristics on methane adsorption heat, five different types of rank coals were used for low-pressure nitrogen, low-pressure carbon dioxide, and methane adsorption experiments. Pore structure and adsorption parameters, including maximum adsorption capacity and adsorption heat, were obtained for five coal samples, and their relationships were investigated. The results show that the low-pressure nitrogen adsorption method can measure pores within 1.7–300 nm, while the low-pressure carbon dioxide adsorption method can measure micropores within 0.38–1.14 nm. For the five coal samples, comprehensive pore structure parameters were obtained by combining the results of the low-pressure nitrogen and carbon dioxide adsorption experiments. The comprehensive results show that micropores contribute the most to the specific surface area of anthracite, lean coal, fat coal, and lignite, while mesopores contribute the most to the specific surface area of coking coal. Mesopores contribute the most to the pore volume of the five coal samples. The maximum adsorption capacity has a significant positive correlation with the specific surface area and pore volume of micropores less than 2 nm, indicating that methane is mainly adsorbed on the surface of micropores, and can also fill the micropores. The adsorption heat has a significant positive correlation with the specific surface area and pore volume of micropores within 0.38–0.76 nm, indicating that micropores in this range play a major role in determining the methane adsorption heat.

Characteristics of pores in coals exposed to acid mine drainage

Acid mine drainage commonly occupies some pore space after underground coal mining, and this severely depreciates coal pillars, thereby posing a significant risk to mine stability. Considering that such depreciation is reflected in the microstructures of these pillars, in the present study, we propose a static immersion method suitable for coal seam samples immersion in the laboratory. We immersed the No. 2–2 coal seam samples from the Ningtiao Tower Coal Mine in Yulin, Shaanxi Province, in different acid mine drainage solutions and monitored the pH, oxidation–reduction potential (ORP), electrical conductivity (EC), total dissolved solids (TDS) among other water quality parameters for 300 h. After the immersion tests, samples were examined using scanning electron microscopy (SEM). The pH, ORP, EC, and TDS of the prepared acid mine drainage solutions increased significantly as the immersion time increased. Changes in water quality parameters are attributed to the absorption of hydrogen ions by insoluble clay minerals in the coal, which reduced the acidity, increased the pH value, and enhanced the electrical conductivity of the acid mine drainage solutions. SEM analysis reveals differences in the pore characteristics of (pore throat size and orientation) of the coal samples, and these are caused by erosive effects of the acid mine drainage solutions. Pores with throat sizes greater than 10μm increased by 95% as the pH of the acid mine drainage solutions decreased, while the dominant pore orientation (60–90°) decreased to the 0–30° or increased to the 150–180° range, thereby increasing their randomness.

Effects of inhibitors on the sequestration of flue gas in goaf and pore structures of coal

Injecting power plant flue gas into goaf for sequestration can not only reduce the emission of CO2, but can also effectively inhibit the spontaneous combustion of coal left in the goaf. To analyze the effect of the chemical environment in the goaf on the sequestration of CO2 in a coal seam, a home-made adsorption experiment device and ASAP 2020 specific surface analyzer were used to study the regularity of CO2 adsorption in coal and the pore structure of coal before and after inhibition. The results indicate that the adsorption capacity of CO2 in coal increased by 14.05%–21.04% after inhibition. The inhibitors can significantly increase the adsorption capacity of CO2 in coal, enhancing the sequestration of flue gas in goaf.The pore volume and specific surface area of micropores in the coal samples after inhibition are larger compared to those in the raw coal, whereas those of mesopores and macropores are smaller, but those of the micropores are 4.3 and 205 times those of mesopores and macropores, respectively. Thus, the total pore volume and specific surface area of coal increased significantly after inhibition, which is the reason for the increase of CO2 adsorption capacity. The inhibitor does not fundamentally change the pore size distribution of coal, most of the pores in coal are in the pore size range of 0.4–0.6, 0.8–0.9, 1.5–75, and 120–170 nm, which greatly contribute to its pore volume and specific surface area. The pores with a pore size of <7.5 nm are the main adsorption pores in coal, and the inhibitors can significantly increase the number of micropores and mesopores with a pore size of <7.5 nm. The fractal dimension of the coal samples was calculated using the FHH model, which indicated that the intrusion of inhibitors can remove the impurities in pores and reduce the surface roughness of coal. Conversely, the macropores in the coal samples after inhibition are broken and new micropores are generated. This study is of great significance for increasing the sequestration capacity of CO2 in goaf.

Research on coalbed methane microscopic seepage characteristics of medium and high-rank coal

ABSTRACT In the present study, the microscopic seepage characteristics of coalbed methane (CBM) in medium and high-rank coal are investigated. Moreover, the influence of the coal pore structure on the CBM migration is studied. To this end, X-ray μCT scanning technology is utilized to construct the microscopic pore structure model of medium and high-rank coal. Then, the established model is transformed into a vectorized CAD solid model. Numerical simulation under different working conditions is carried out. The obtained results show that the pore system of coal is in a connected state. However, not all pores can penetrate the entire seepage direction. It is found that pore connectivity is the most important factor determining the CBM seepage performance. As coal metamorphism increases, the corresponding seepage pore connectivity decreases, pore throat radius decreases, seepage channels in coal seams decrease and the coal permeability decreases. Meanwhile, permeability anisotropy and the pore pressure of the coal have different changing laws along different seepage paths. It should be indicated that there is a dominant seepage direction. As the degree of coal metamorphism increases, the permeability in all directions gradually decreases.

Experimental study of effect of slickwater fracturing on coal pore structure and methane adsorption

Driven by high pressure, slickwater may intrude into the pores of coal seams, causing changes in the pore structure, and ultimately affecting the flow of Coalbed Methane (CBM). In this study, slickwater prepared with different concentrations of polyacrylamide (PAM) is used to soak coal samples from Inner Mongolia under high pressure to explore the effect of slickwater fracturing on coal seam pores. To study the evolution characteristics of the pore structure of coal samples treated with slickwater, low temperature nitrogen adsorption experiments and methane adsorption experiments are combined. The experimental results show that under the action of external pressure, slickwater invades the pore structure of coal, resulting in a significant decrease in pore volume and specific surface area. Furthermore, with the increase of the pressure and viscosity of the slickwater, the slickwater residue blocks the micropores in the coal pore structure more severely. The damage to methane adsorption by residue is more serious than that to nitrogen adsorption, reflecting that more residue remains in the micropores of coal samples. The development of a gel breaker suitable for slickwater can promote the degradation of PAM polymer molecules and the reduction of residual liquid viscosity after fracturing, and improve the flowback effect. This may be an effective way to reduce reservoir damage.

Correlation mechanism between the law of ultrasonic propagation in coal samples and the migration of water

In order to reveal the correlation mechanism between the law of ultrasonic propagation and water migration. A simulation method for displaying the entire process of multi-field coupling ultrasonic excitation, propagation, and reception based on CT scanning reconstruction of the coal pore–fracture structure model is proposed. A porous medium water migration-ultrasonic wave propagation calculation model is constructed by introducing the water-injected coal porous medium water migration calculation model into the ultrasonic propagation calculation process. In the simulation analysis, the coal sample matrix and minerals reconstructed by CT scanning are regarded as homogeneous elastic materials, and the contribution of water migration to the elastic parameters is characterized in the form of equivalent parameters. The pore fracture is regarded as a pressure acoustic fluid, and the equivalent parameter method is used to characterize the water–gas distribution in the pore fracture. The electrostatic coupling solid mechanics and solid mechanics coupled pressure acoustics mode are used to simulate the propagation process of the ultrasonic wave excited by the ultrasonic transducer in the water-injected coal sample, thereby revealing the law of ultrasonic wave propagation in the water-injected porous medium. Research results show that the transmission rate of the ultrasonic wave decreases when the ultrasonic wave propagates to the location of the mineral, and the mineral transmits part of the displacement energy of the ultrasonic wave and partly reflects this energy. The first position reached during the ultrasonic propagation is the position where the fractures are slightly obstructed followed by after reflection, superposition, and finally full distribution. The water accelerates the propagation velocity of ultrasonic waves. However, the capability of ultrasonic waves to pass through the fractures slightly contributes to the presence of water inside the fractures and mainly depends on whether the migration of the coal matrix water covers the fracture area.

N2 injection to enhance coal seam gas drainage (N2-ECGD): Insights from underground field trial investigation

Pre-gas drainage plays a significant role of preventing gas disasters in underground coal mines. However, it is difficult to reduce the gas content to below the threshold values, especially in low permeability coal seams in China. Previous field trials on the enhanced coalbed methane recovery (ECBM) by nitrogen injection mostly focused on the ground. Until now, few attempts on N2 injection to enhance coal seam gas drainage (N2-ECGD) and no sufficient evidences can indicate the good effect. In this study, exploratory tests of N2-ECGD were carried out in underground low-gas coal seams (with gas content less than 5 m3/t). An experiment to displace the CH4 in coal by N2 injection under constant pressure conditions was first carried out. The results show that continuous N2 injection can promote the desorption of CH4 in the coal pores, which cannot be achieved under normal pressure. N2-ECGD field trials were conducted in the working face of a coal mine in Hejin City, Shanxi Province, China. The effective pressure of N2 injection (EPI) was investigated. Intermittent and continuous N2 injection trials were carried out to study the response characteristics of the gas flow rate, CH4 concentration, and flow rate. The results show an EPI of 0.45 MPa and gas injection radius of 5 m. The gas flow rate increased significantly after N2 injection. Although the CH4 concentration decreased, the CH4 flow rate remained high. On the basis of the change characteristics of gas drainage parameters, the physical process of N2-ECGD was analyzed. The research results obtained in this study can serve as a reference for the application of N2-ECGD in low permeability coal seams. The study also provides a new technical approach for local gas prevention and control in underground coal mines.

Experimental Research on the Performance of a Wetting Agent Based on Compound Acidification in Low-Porosity and Hard-to-Wet Coal Seams.

To improve the wetting performance of the composite acid solution in the deep coal seam, in this paper, the surface tension and contact angle characteristics of the compound acid wetting agent are studied, then the composition of the wetting agent is developed and evaluated based on nuclear magnetic resonance. The research indicates that surfactants can reduce the surface tension of water, and the surface tension tends to decrease with the increase in the surfactant concentration. The critical micelle concentration of the anionic surfactant sodium dodecyl sulfate (SDS) solution is only 0.025%, and the corresponding critical surface tension is 30.63 mN/m. The wetting agent material based on the composite acid solution includes the acid HCl, HF, the anionic surfactant SDS, and the inorganic salt NaCl, the composition of which is 8%, 8%, 0.025%, and 0.6 mol/L, respectively. The total wetting rate of the composite acid-containing HCl + HF + SDS + NaCl is the largest, reaching 64.30%, which has good wettability inside the coal and can be a comprehensive intrusion into the internal structure of coal pores.

Comparative analysis of pore structure parameters of coal by using low pressure argon and nitrogen adsorption

The accurate characterization of coal pore structure is of great significance for in-depth understanding of interior properties and gas adsorption, desorption and diffusion characteristics. In this study, the low pressure argon adsorption (LP-ArGA) and low pressure nitrogen adsorption (LP-N2GA) were all used to analyze the pore parameters of coal with different metamorphism. The results indicated that the adsorption isotherm type and desorption hysteresis type of coal samples obtained by the LP-ArGA and LP-N2GA belong to the same type, but the adsorption capacity of the former is higher than that of the latter. The pore size distribution (PSD) of coal samples shows a significant multi-peak distribution feature. Compared with the LP-N2GA, the LP-ArGA can accurately analyze the pore parameters between 2 and 4 nm or part of 2–7 nm. The mesopore volumes obtained by the LP-ArGA is 1.66–2.84 times that of the LP-N2GA, and there is no obvious law of macropore volume. The macropore volumes of QN and PM samples decreased by 17.2% and 50.9%, respectively, while GHS sample increased by 166.0%. The corresponding specific surface area (SSA) showed the same properties. Fractal curve fitting results obtained by the two methods are highly correlated, but compared with LP-ArGA, D1 and D2 obtained by the LP-N2GA can well reflect pore characteristics. The fractal dimension obtained by the two methods and the variation trend with the metamorphic degree are all different, which is mainly due to the difference of adsorption volume. The purpose of this paper is to introduce a new method for the analysis of coal pore structure in order to better understand the pore characteristics.

Pore and fracture development in coal under stress conditions based on nuclear magnetic resonance and fractal theory

In this paper, triaxial compression tests on coals with real-time T2 and MRI (Magnetic Resonance Imaging) image measurement are performed by using a nuclear magnetic resonance (NMR) testing system equipped with a loading device. Pore and fracture development in coal under stress conditions are investigated based on NMR and fractal theory. The results show that the accumulation of NMR signal intensity as well as sample porosity decrease slightly at first, then increase slowly, and finally increase rapidly during the deformation of coal. The measured T2 distributions indicate that stress damage mainly induces the generation of mesopores and macropores (or micro-fractures). A new method for estimating crack-initiation stresses is proposed based on the evolution of T2 curve. By using this method, we estimate the crack-initiation stress of the tested coal samples, which is 34.6%, 32.2%, and 30.1% of its corresponding peak strength, respectively. Fractal dimensions of seepage pores show significant fractal characteristics, while fractal characteristics of adsorption pores are not obvious. The evolution of fractal dimension DT of the total pores with stress is similar to the changing trend of porosity. But the fractal dimension of DS shows a negative correlation with the stress.

3D reconstruction of coal pore network and its application in CO2-ECBM process simulation at laboratory scale

3D reconstruction of coal pore network and its application in CO2-ECBM process simulation at laboratory scale

Differential Strain Index-Based Multiphysics Model for Coal Seam Gas Production

Conventional multiphysics for coal seam gas production is generally coupled with poroelasticity-based coal permeability models, which are derived under the assumption that gas pressure is distributed uniformly within the representative elementary volume (REV). Under this assumption, the pore swelling/shrinking strain is equal to the bulk one. However, this assumption is considered as the primary reason for the inconsistency between experimental data, field data, and model results. In this study, a new concept of differential strain index (DSI) is proposed to theoretically define the relation among desorption-induced strains of the coal bulk, pores and solid grains. DSI is a function of the gas pressure, and its magnitudes are regulated by the Langmuir constants of both the solid grains and the coal bulk. Furthermore, a DSI-based coal permeability model is incorporated into the coupled multiphysics model for coal seam gas production. The model results of both laboratory-scale and field-scale show that coal permeability changes over a wide range during gas production. These changes are controlled by the DSI, and the magnitudes of change are defined by the Langmuir strain ratio of solid grains to coal bulk, while the trends of change are defined by the Langmuir pressure ratio of solid grains to bulk coal.

High-pressure water and gas alternating sequestration technology for low permeability coal seams with high adsorption capacity

Traditional ECBM techniques, which cannot extract methane adsorbed in coal pores effectively, is still difficult to greatly improve coalbed methane recovery rate until now. Waterflooding or CO2-ECBM can displace methane adsorbed in nanopores but increases the risk of coal and gas outbursts. We proposed a novel coalbed methane recovery technique, e.g. high-pressure water and gas alternating sequestration technique (H–P-WGAS), which can displace adsorbed methane in coal pores without introducing other gases with high adsorption capacity. Additionally, the injected H–P gas can eliminate the water lock and be easily extracted during methane drainage. Numerical simulation and field test were conducted to verify effectiveness of the H–P-WGAS technique. The numerical results show that the H–P-WGAS technique can enhance methane migration in coal seam by changing pore pressure distribution and increase influence radius to 70 m at 20 MPa in 48 h. For water and air co-injection, methane content can decrease by up to 37.6%, which is much more effective comparing with that under single water injection or gas injection. Meanwhile, field tests show that the reduction of methane content by percentage lies between 25.14% and 80.62% with an average of 53.17%. Meanwhile, the influence radius of field test reached ∼48 m. The average methane drainage flow rate of single borehole increased by 2.65 times. Average methane drainage concentration increased from 31.3% to 47.6%. The methane drainage flow rate and concentration of the whole coal mine increased by 50.2% and 32.4%, respectively. The above results indicate that the proposed H–P-WGAS has best effectiveness comparing with single water injection or air injection.

Effect of different types of fracturing fluid on the microstructure of anthracite: an experimental study

ABSTRACT A systematic understanding of the effects of different fracturing fluids on the chemical and pore structure of coal is of great significance for the exploitation of coalbed methane (CBM). In this study, Fourier-transform infrared spectroscopy and mercury intrusion porosimetry were used to analyze the chemical and pore structure of coal samples treated by different fracturing fluids. The results show that fracturing fluid treatment has little effect on the coal aromatic structure. The oxygen-containing and hydroxyl structures of the coal samples treated by acidic and viscoelastic surfactant (VES) fracturing fluids increased by >17%, which is beneficial for gas desorption and thereby increases CBM yield, whereas those of the coal sample treated with deionized water decreased by 3.8%. The acidic and VES fracturing fluid treatments are also beneficial for coal pore connectivity, which promotes gas migration. The three types of fracturing fluids increased the macropore volume by >350%. The deionized water treatment reduced mesopores and micropores by 20% and 5%, respectively, while the transition pores increased by 2.3%, resulting in a 2.6% increase of the specific surface area, which is not conducive to gas desorption and migration. The acidic fracturing fluid treatment increased the mesopore volume by 53.3%, reduced the transition pore and micropore volumes by 5.3% and 32.5%, respectively, and reduced the surface area by 13.2%, which reduces the amount of adsorption sites and facilitates gas migration. However, the adsorption pores and mesopores after VES fracturing fluid treatment decreased by 17.6% and 26.7%, respectively, which indicates that this treatment does not transform most adsorption pores into migration pores.

Research on the Influence of Gas on Coal Pores based on NMR Technology

In order to study the change characteristics of the pore structure of coal under different CH4 pressure conditions, nuclear magnetic resonance (NMR) technology was used to test the degree of influence on porosity and pore size distribution of coal after the adsorption of CH4 under different pressures. The test results show that under the action of gas pressure, the NMR signal amplitude of the NMR T2 spectrum changes significantly. From the distribution area of the T2 spectrum of the coal sample, it can be known that the peak peak area of small holes&gt;the peak peak area of medium and large holes&gt;the peak peak area of cracks indicates that the coal sample The micropores in the coal body are the most developed, and the connectivity is not strong, and it is difficult to circulate; in the range of gas pressure P=0.5~2.0MPa, as the gas pressure increases, new pores will be generated in the coal body, and the micropores are interconnected to form micropores or medium Pores and mesopores are interconnected to form cracks, thereby increasing the porosity and permeability of the coal sample.

Experimental research on the effect of plasma on the pore-fracture structures and adsorption-desorption of coal body

This paper is aimed at investigating the influence of plasma technology on desorption and adsorption features of coal in the fracture scale and proving that plasma technology boasts a wide prospect in the field of coalbed methane extraction. In this paper, CT was combined with low-temperature liquid nitrogen adsorption to analyze the pore and fracture variations of coal before and after plasma breakdown. More importantly, a self-designed desorption experimental system was used to explore variations of gas desorption with time in the fracture scale. According to the research results, the fragmentation effect of plasma is reflected by the generation of cracks in the macro-scale and the improvement of pores in the micro-scale; the fracture is generated from the section near the electrode, and the fracture growth rate after breakdown can reach 18–41 times; the action of plasma can crush coal into little pieces and promote the porosity by over hundreds of times. The appearance of semi-open pores in the liquid nitrogen adsorption test shows that part of closed pores in the coal body are opened by plasma. Moreover, the plasma channel can weaken the adsorption capacity of coal to gas, which is similar to the temperature effect. Meanwhile, the plasma channel increases the desorption amount of coal by 50%–70% and greatly improves the desorption rate of coal due to the influence of interconnected cracks.

Accurate characterization of coal pore and fissure structure based on CT 3D reconstruction and NMR

In order to accurately achieve the full-scale characterization of coal pore and fissure structure, a comprehensive characterization method based on Computed Tomography (CT) 3D reconstruction, Nuclear Magnetic Resonance (NMR) T2 spectrum and Nuclear Magnetic Imaging (NMI) are proposed. CT scanning and NMR experiments are carried out on the samples of gas coal and anthracite to verify this method. And the characteristics of pore size distribution (PSD), porosity and permeability are studied. It is found that the main seepage channels can be obtained by CT 3D reconstruction, and that the observation defect of CT scanning can be compensated by NMI because micro seepage pores and adsorption pores can be visualized. Furthermore, CT 3D reconstruction results indicate that the larger the pore size, the smaller the number of pores, and the larger the porosity component while the NMR T2 spectrum of pore size distribution show that the porosity component of micro adsorption pores is largest. With the advantage of CT macro-scale observation and NMR micro-scale observation combined, porosities are calculated accurately. Besides, seepage characteristics observed in the NMR experiments under different water injection pressures are analyzed, and the results are consistent with the analysis results of the CT 3D reconstruction of coal connectivity.

Experimental evaluation of ultrasound treatment induced pore structure and gas desorption behavior alterations of coal

Effective reservoir stimulation is the key for enhancing coalbed methane (CBM) recovery. Ultrasound treatment provides a novel alternative to traditional hydraulic fracturing for gas drainage from coal formations. An improved understanding of the ultrasound effect on coal structure and gas desorption and transport behavior through coal is essential for the potential field implementation. This study aims to investigate the pore/fracture structure alteration with ultrasound treatment for coal and its implication on gas desorption and diffusion behaviors. We used multiple techniques, including nuclear magnetic resonance (NMR), low pressure nitrogen adsorption (LPNA) and gas desorption/diffusion experiments, to characterize the pore structure alterations and its implication on the gas desorption and diffusion behaviors of coal. The NMR tests show that the pore volume and their overall interconnectivity in coal increase with ultrasound treatment. With the ultrasonic treatment (25 kHz, 18 kw, 2 h), the porosity increases by 9.6%–11.9%, and the permeability increases by 21.5%–40.7% for the tested coal. Based on the experimental data, ultrasonic treatment can effectively modify the coal pores within size range of 1 nm–100 nm, and the greater power of ultrasound leads to the greater effect on the pore alteration in coal. After being treated with ultrasound (25 kHz, 3–18 kw, 2 h), the average pore diameters of the tested coal increased by 5.05%–61.81%. It was found that the micropore dilation due to mechanical vibration and cavitation effects can effectively convert micropores into the meso-/macro-pores during the ultrasonic treatment. The results demonstrate that ultrasound treatment changes the coal structure and significantly increases the N2 accessible specific surface area and pore volume in coal. These results can jointly make positive impact on the gas transport during the gas drainage and CBM production.

Effect of dominated coal pores and fractures on water migration after low-pressure water injection based on CT images

A computational model for water migration in porous media is developed based on the CT images of coal samples to study the effect of dominant pores and fractures on water migration after low-pressure water injection. The pore and fracture structure in this model is regarded as porous media with a porosity ratio close to 1, and the fluid exchange between the pores and fractures and the matrix area is considered. The effect of pore and fracture structure on water migration is determined through numerical solution. Results show that the velocity of the fluid flowing into the matrix from the corner of the fracture increases significantly. Moreover, the efficiency of water migration in the radial fractures is high, and water tends to flow to the radial fractures. The pores mainly play a role in quickly absorbing and efficiently transporting water. The non-connected pores can increase the range of water migration and should not therefore be ignored. The role of pores and fractures in dominating water migration is most obvious at the front edge of water migration. The water migration is divided into three stages: high-velocity, transitional, and low-velocity migration stages. In addition, the distance difference between the saturation contours of water migration has a logarithmic relationship with time, and the macro fractures around the boreholes cause the increase in the distance difference between the two saturation contours.