Increasing Water Saturation Research Articles

A novel approach for wettability estimation in geological systems by fluid–solid interfacial area measurement using tracers

Wettability plays a vital role in many applications of flow in porous media and affects Darcy scale flow parameters by influencing the fluid–solid interfacial area. Therefore, quantifying the fluid–solid interfacial area can provide a way to measure wettability at the Darcy scale. Here, we experimentally explore a dual-tracer method, which can also be scaled to large geological reservoirs to quantify the fluid–solid interfacial area during the multiphase flow through a porous medium for different wetting conditions. Using our experiments, we demonstrate the influence of different saturations, wettability and flow conditions on the solid–liquid interfacial area. When oil is in the residual phase, we observe that the solid–water interfacial area increases with the increase in water saturation for the water-wet and mixed-wet cases. However, the water–solid interfacial area decreases with an increase in water saturation for the oil-wet case. We increase the water saturation by increasing the water flow rate; therefore, the anomalous behaviour seen in the oil-wet case can be attributed to the rearrangement of oil and water at higher water flow rates. When both oil and water are flowing, the solid–water interfacial area increases with water saturation for all the wettability cases and increases in water wettability as anticipated.Synopsis: Wettability measurements at Darcy-scale give a broad idea of overall subsurface wetting conditions for application in CO2 sequestration, ground-water remediation or oil recovery.

CO2 enhanced gas recovery and sequestration as CO2 hydrate in shallow gas fields in Alberta, Canada

In this study, we carry out reservoir simulations to investigate the effect of CO2 hydrate formation on CO2 storage capacity in shallow gas fields. Results show that CO2 hydrate formation moderates the reservoir pressure due to volume shrinkage thus allowing more CO2 (122–212% pore volume) to be stored. The CO2 storage capacity in a gas field with CO2 hydrate formation is up to 3.2 times that without CO2 hydrate formation. Due to CO2 hydrate formation, the CO2 storage capacity in a gas field first increases when initial water saturation increases from 0.1 to 0.3 but then decreases when the initial water saturation increases from 0.3 to 0.5. However, the CO2 storage capacity decreases with an increase in initial water saturation if there is no CO2 hydrate forms. Results of screening show that out of 68,327 gas fields in Alberta, 517 gas fields can be used to store CO2 as CO2 hydrate, giving a total CO2 storage capacity of 536 Mt. Of this, depleted gas fields in Alberta have the highest CO2 storage capacity including the Chard and Saleski gas fields with storage capacity of 138 Mt and 94 Mt, respectively.

Integrated geophysical investigation for understanding agriculturally induced landslides in southern Peru

We conducted near-surface geophysical surveys in and around the Majes I agricultural development (60 km west of Arequipa, Peru), where the nexus of geology and agriculture has increased landslide activity along the Majes–Siguas River Valley. Through DC resistivity, transient electromagnetics (TEM), and seismic surveys, we refined the understanding of local geology, characterized the agricultural impact on the local water table, and updated landslide modeling to help inform discussions on landslide mitigation strategies at Majes I and landslide prevention at the planned Majes II site. At the Majes I development, we identified an increase in water table and water saturation due to irrigation. At the planned Majes II site, which shares similar geology to Majes I, we interpret the regional water table that has yet to be affected by significant human development. We integrated these results into updated landslide modeling. Our modeling for Majes I suggests stable conditions prior to irrigation; as the water table rose from irrigation, landsliding began and evolved as a retrogressive failure that is now focused along the headscarp near critical infrastructure including the Carretera Panamericana (Pan-American Highway). Majes II is currently stable and irrigation management, such as drip versus flood techniques, must be supported. Soil ameliorants such as polymers and/or biochar should be encouraged to hold water near the roots to reduce the risk of landslide initiation. Combined this work shows the value of integrated hydrological and geophysical research for landslide management and optimized irrigation.

Microscopic modelling of gas diffusivity in unsaturated cementitious materials considering multiple diffusion regimes

Common degradations of concrete including reinforcement corrosion and carbonation are highly associated with the transport of aggressive gases. However, it is still challenging to accurately understand the gas diffusion behaviour and determine the gas diffusivity in unsaturated cementitious materials. This study proposes a pore-scale model for simulating gas diffusivity in unsaturated cement paste covering multiple gas diffusion mechanisms. The representative volume elements of colloidal calcium silicate hydrate and heterogeneous cement paste with various water saturation degrees are established, capturing the structural attributes of hierarchical cement paste and water-gas distribution with minimum surface energy. A finite difference model for diffusion considering Knudsen effect and molecular diffusion is developed to simulate the diffusion process of various gases through partially saturated cement pastes with different pore structures. Results indicate that gas diffusivity decreases with the increasing water saturation level, the evolution of which can be divided into stable, decreasing and non-diffusive stages. The gas diffusion in partially saturated cement paste is highly dependent on the pore structure and diffusive gas type. The results obtained from this study are expected to provide a deeper insight into the solution of diffusion-related durability problems and the prediction of service life of concrete.

Effects of water saturation and loading rate on direct shear tests of andesite

For estimating the long-term stability of underground framework, it is vital to learn the mechanical and rheological characteristics of rock in multiple water saturation conditions. However, the majority of previous studies explored the rheological properties of rock in air-dried and water saturated conditions, as well as the water effects on compressive and tensile strengths. In this study, andesite was subjected to direct shear tests under five water saturation conditions, which were controlled by varying the wetting and drying time. The tests were conducted at alternating displacement rates under three vertical stresses. The results reveal that the shear strength decreases exponentially as water saturation increases, and that the increase in shear strength with a tenfold increase in displacement rate is nearly constant for each of the vertical stresses. Based on the findings of the shear tests in this study and the compression and tension tests in previous studies, the influences of both water saturation and loading rate on the Hoek-Brown failure criterion for the andesite was examined. These results indicate that the brittleness index of the andesite, which is defined as the ratio of uniaxial compressive strength to tensile strength, is independent of both water saturation and loading rate and that the influences of the water saturation dependence and the loading rate dependence of the failure criterion can be converted between each other.

Retracted: Water Transport in GDL Microstructures of Nonuniform Fiber Diameter Arrangement

In proton exchange membrane fuel cells (PEMFCs), the gas diffusion layer (GDL) plays an important role in the transport of reactants, water, heat, and electrons. Microstructure manipulation of porous media via a nonuniform fiber diameter arrangement could potentially be used to improve water transport behavior in GDLs. A numerical modeling approach is used to simulate GDL microstructures with uniform and nonuniform fiber diameters. The reconstructed porous microstructures’ water saturation and porosity are compared. The simulations of three-dimensional (3D) two-phase flow volume of fluid (VOF) models were completed on the OpenFOAM platform using the finite volume method (FVM). Simulations demonstrate that by adopting a nonuniform microstructural fiber diameter design, both porosity and water transport behaviors can be altered. As a result of the nonuniform fibrous arrangement, the ability to improve GDL performance by controlling water transport and porosity is possible. The results indicate that by manipulating the GDL microstructure, additional water pathways can be created, resulting in slightly increased water saturation. We propose that water transport can be improved by microstructural manipulation of the GDL, specifically by optimizing the arrangement and position of nonuniform fibers.

Experimental study on gas permeability of cement-based materials

Gas permeability is an important property associated with the durability of cement-based materials. In this study, an experimental method based on applying a quasi-stationary flow is adopted to evaluate the gas permeability of cement-based materials. The results indicate that the intrinsic permeability of dried cement-based materials is affected by the addition of limestone powder, fly ash, and aggregate. The Katz-Thompson equation could predict the intrinsic permeability by using the capillary porosity, average diameter, and pore tortuosity. The intrinsic permeability of partially saturated cement-based materials decreases when the water saturation increases. The Van Genuchten-Mualem model could describe the relative gas permeability of partially saturated cement-based materials, and the model parameters n value between 1 and 2 while m value ranging from 0.64 to 0.69 for cement and mortar. Moreover, the power function relationship between the intrinsic permeability and Klinkenberg constant of cement-based materials has also been corroborated. Finally, a prediction model of gas permeability of cement-based materials under arbitrary water saturation and pressure gradient is proposed.

A Novel Empirical and Deep Ensemble Super Learning Approach in Predicting Reservoir Wettability via Well Logs

Accurately measuring wettability is of the utmost importance because it influences several reservoir parameters while also impacting reservoir potential, recovery, development, and management plan. As such, this study proposes a new formulated mathematical model based on the correlation between the Amott-USBM wettability measurement and field NMR T2LM log. The exponential relationship based on the existence of immiscible fluids in the pore space had a correlation coefficient of 0.95. Earlier studies on laboratory core wettability measurements using T2 distribution as a function of increasing water saturation were modified to include T2LM field data. Based on the trends observed, water-wet and oil-wet conditions were qualitatively identified. Using the mean T2LM for the intervals of interest and the formulated mathematical formula, the various wetting conditions in existence were quantitatively measured. Results of this agreed with the various core wettability measurements used to develop the mathematical equation. The results expressed the validity of the mathematical equation to characterise wettability at the field scale. With the cost of running NMR logs not favourable, and hence not always run, a deep ensemble super learner was employed to establish a relationship between NMR T2LM and wireline logs. This model is based on the architecture of a deep learning model and the theoretical background of ensemble models due to their reported superiority. The super learner was developed using nine ensemble models as base learners. The performance of nine ensemble models was compared to the deep ensemble super learner. Based on the RMSE, R2, MAE, MAPD and MPD the deep ensemble super learner greatly outperformed the base learners. This indicates that the deep ensemble super learner can be used to predict NMR T2LM in the field. By applying the methodology and mathematical formula proposed in this study, the wettability of reservoirs can be accurately characterised as illustrated in the field deployment.

Effective medium modeling of the joint elastic-electrical properties of sandstones with partial water saturation

Quantitatively assessing fluid saturation in reservoir rocks has been the ultimate goal of hydrocarbon geophysical investigations. Joint interpretation of acoustic and electromagnetic survey data indicates a promise to improve the fluid quantification ability. However, the saturation effects on the cross-property relationship between the elastic and electrical rock properties (i.e., the joint elastic-electrical properties) that form the key to the successful joint interpretation remain poorly understood. We have developed an effective medium modeling scheme for the joint elastic-electrical properties of sandstones with partial water saturation and studied theoretically the effects of porosity and grain and pore geometries on the saturation-dependent joint elastic-electrical properties of sandstones. Comparison between the modeling results and an available laboratory data set confirms the applicability of the approach for modeling the joint elastic-electrical properties of partially saturated sandstones. P-wave velocity is found to decrease with increasing electrical conductivity as water saturation increases in rocks with low porosity, low grain aspect ratio, and high pore aspect ratio. The water saturation effects on the joint properties are amplified in rocks with higher porosity, greater grain aspect ratio, and lower pore aspect ratio, in which P-wave velocity indicates an asymmetric V-shaped relationship with electrical conductivity as an implicit function of increasing water saturation. It also is found that the increasing porosity affects the joint properties in a gradually increasing manner, whereas the increasing grain and pore aspect ratios impose a decreasing impact on the joint elastic-electrical correlations. The results have strengthened our understanding of the joint elastic-electrical properties of partially saturated sandstones and will facilitate the joint interpretation of acoustic and electromagnetic survey data for improved fluid quantification.

Numerical study of the mud loss in naturally fractured oil layers with two-phase flow model

Drilling in the naturally fractured formations always encounters severe mud loss, which endangers the drilling safety. In oil & gas layers, a larger quantity of mud loss has great adverse effects on later oil and gas production. Therefore, it makes the knowledge of mud loss very important, and after that, it is instructive to control the mud loss in the oil layer. In this paper, we first consider the mud loss process using a two-phase flow model. A discrete fracture network model is employed to describe the fluid transfer between fractures and matrix pores. And different relative permeability curves and capillary pressure functions are used in matrix pores and natural fractures. The finite element method and “upwind” scheme are employed to deduce the numerical discretized formulas. The correctness of our model is verified with the published literature. Then a sensitivity analysis is performed to study the laws of mud loss in naturally fractured oil-wet formation. Compared with single-phase flow models, the mud loss rate of two-phase flow model is lower. The two-phase flow model is used to identify the most influential factors on mud loss and predict the distribution of water saturation in oil formation during the drilling process. We find that: since the pressure increase zone is much larger than the water saturation increase zone, the size of the water invasion zone is unknown in the single-phase flow model. The most important influential factors of mud loss in the oil layer are fracture connection, drilling fluid density and matrix permeability. Once the natural fractures are connected to the wellbore, the mud loss rate is much higher than that when the natural fractures are not connected to the wellbore. The capillary pressure has little effect on the mud loss. The larger the capillary pressure, and the lower the mud loss rate. The model in this paper is instructive to learn the law of mud loss and contamination range of drilling fluids in oil layers.

Influence of water on thermo-oxidative behavior and kinetic triplets of shale oil during combustion

The oxidation reactions between oxygen and shale oil directly affect the feasibility and performance of air injection. In this work, the influence of water on thermo-oxidative behavior of shale oil was studied using high-pressure differential scanning calorimetry (HP-DSC). Subsequently, the kinetic triplets for shale oil oxidation in the absence and presence of water were determined using Friedman and Ozawa-Flynn-Wall (OFW) models as well as one advanced integral master plots method. The HP-DSC results showed that at 5 MPa, the shale oil was vulnerable to obviously higher heat release at the low-temperature oxidation (LTO) region compared to the high-temperature oxidation (HTO) region, resulting in shortening the oxidative induction time and achieving in-situ upgrading of shale oil. Water delayed the initial heat release due to the fact that heat release yielded by LTO compensated the heat adsorption yielded by evaporation of water and light hydrocarbons. Additionally, the heat release was reduced with the elevated water saturation as a result of the reduction in exothermic rates and intensified evaporation of water and light hydrocarbons. The higher energy was needed to trigger off the LTO reactions while increasing water saturation from 10% to 20%. Therefore, it was believed that the presence of water extended the oxidative induction time, thereby hindering the smooth and rapid transition from the LTO to HTO stages. Water changed the reactivity of each oxidation stage for shale oil, resulting in higher energy required for the initial LTO reactions and lower energy required for the subsequent oxidation reactions. The water saturation range of 10% to 15% could accelerate the occurrence of high-temperature combustion most effectively, demonstrated by values of activation energy for the conversion greater than 0.6. The appropriate oxidation reaction models for shale oil alone and water saturations of 10%, 15%, and 20% were determined to be D2, F1, F3, and R3, respectively. The determination of kinetic triplets assisted in building the reaction schemes for modelling the air injection process of shale oil reservoirs.

Impact of water saturation on diffusion coefficients determined by constant volume diffusion method

In recent decades, carbon dioxide (CO2) injection has become a promising technique for enhanced oil recovery (EOR). To design and model the CO2-EOR process in a petroleum reservoir, knowledge of the molecular diffusion of CO2 in oil is required. In this research, the constant volume diffusion (CVD) method is utilized to determine the diffusion coefficient of CO2 in a core saturated with synthetic oil. In addition, the effect of the water saturation level in the core on the resulted diffusion coefficients is examined. This method includes an oil-saturated core, which is in direct contact with a CO2 chamber. CVD tests were conducted at initial pressure and temperature of 410 psi and 64°C for water saturation of 0, 39, and 53%. CO2 is injected from the top of the core and oil is produced from the bottom. Once the CVD initial condition is established, the injector and producer valves are shut-in and the CVD test starts. In the CVD test, the pressure drop data are collected and used to tune the diffusion coefficients using a compositional reservoir simulation model equipped with a developed equation of state. History matching of the pressure decay data is conducted to determine the tuned diffusion coefficients. Experimental results show that the existence of water in the core causes a smaller pressure drop in the system. We find that diffusion coefficients decrease linearly with increasing water saturation in the core operating at the same initial pressure and the system temperature. The presence of water in the core reduces the rate of CO2 diffusion into the synthetic oil. Finally, we present an empirical relationship of the diffusion coefficient and the irreducible water saturation at the proposed lab conditions.

Effect of Initial Water Saturation on Oil Displacement Efficiency by Nanosuspensions

This article deals with the study of the initial water saturation effect of a porous medium on the oil recovery factor using a water-based nanosuspension. The initial water saturation of the porous medium in the computations varied within the range from 0 to 90%. The nanoparticle SiO2 concentration varied from 0 to 1 wt%. The particle sizes were equal to 5, 18, 22, and 50 nm. Experimentally measured wetting angles and the interfacial tension coefficient depending on the concentration and size of nanoparticles were used in computations. A mathematical model was developed, describing the transfer and diffusion of nanoparticles within the aqueous phase during immiscible displacement of oil by nanosuspension from a porous medium. Using the developed model, a systematic computational study of the effect of the initial water saturation of the core micromodel on the oil recovery factor using nanosuspension was carried out. It was revealed that with an increase in the initial water saturation, the oil recovery factor monotonically decreased in the case of displacement both by water and nanosuspension. It was shown that with an increase in the concentration of nanoparticles and a decrease in their size, the oil recovery factor increased. At that, the relative increase in the recovery factor had a maximum at an initial water saturation equal to 60%.

Effects of pore connectivity and water saturation on matrix permeability of deep gas shale

Shale matrix permeability is an important indicator for evaluating gas transport and production. However, the effects of pore connectivity and water saturation on the matrix permeability in deep gas shales have not been adequately studied. In this study, the permeability of deep shales in the Yichang area of the Middle Yangtze was characterized using three methods. These included the determination of apparent permeability in different directions via pulse-decay, also matrix permeability obtained via the Gas Research Institute method, and the connected pore network permeability via the mercury injection capillary pressure technique. The results revealed a significant difference between the horizontal and vertical permeability of deep shales. The smaller the size of the multiple connected pore network, the larger was the effective tortuosity and the lower the permeability. Comparison of the three permeabilities and combined microscopic observations revealed that microfractures and laminae were the dominant gas transport channels. Importantly, the matrix permeability decreased exponentially with increasing water saturation, with water vapor adsorption experiments revealing that water occupation of pores and pore-throat spaces smaller than 10 nm in diameter was the main reason for this decrease in matrix permeability. Collectively, proposed method of evaluating effective permeability with an index for shale gas reservoirs is significant for sweet spot selection and production prediction of shale gas reservoirs around the globe. Cited as: Zhao, J., Sun, M., Pan, Z., Liu, B., Ostadhassan, M., Hu, Q. Effects of pore connectivity and water saturation on matrix permeability of deep gas shale. Advances in Geo-Energy Research, 2022, 6(1): 54-68. https://doi.org/10.46690/ager.2022.01.05

COMPARATIVE ANALYSIS ON IMPACT OF WATER SATURATION ON THE PERFORMANCE OF IN-SITU COMBUSTION

The amount of oil together with the water Originally in Place (OIP), makes up the liquid phase in heavy oil reservoir systems. This amount of liquid present in the pores of the reservoir system is known as liquid saturation, plays a vital role in improving oil recovery through In-Situ Combustion (ISC) process. The oil phase acts as fuel in generating thermal energy required for viscosity reduction and the water phase supports in the formation of an enlarged condensation zone that aids in higher mobility of the low viscous oil. A numerical investigation is carried out to study the role of water saturation on the performance of in-situ combustion in a heavy oil reservoir. A finite-difference based numerical model is developed and validated for water recovery. The model is then used to carry out the impact of liquid saturation on the performance of the ISC, as it plays a vital role in screening criteria for the selection of ISC. The numerical results projected a significant effect on the thermal and production profile during the process. A comparison between the effect of variation in water and oil saturations projected a significant increase in reservoir temperatures with increased water saturation than the oil saturation. The highest reservoir temperatures are observed at the maximum liquid (oil and water together) saturation. Further, the additional water drive provided by increased water saturation is observed to contribute to early production rates.

Influence of water on elastic deformation of coal and its control on permeability in coalbed methane production

The permeability of the coal reservoir is affected by the stress caused by water production and matrix shrinkage caused by methane desorption, and its change rate is mainly affected by the elastic parameters of coal, namely Young's modulus (E) and Poisson's ratio (v). E and v will change with the change of coal water saturation, which will affect the reservoir permeability, but there is little research on it. Therefore, in this study, triaxial compression experiments were carried out on high volatility bituminous coal samples with different water saturation to obtain the variation law of E and v with water saturation. Combined with gas permeability experiments of coal samples with different water saturation and finite element method, the influence of E and v on permeability change were analyzed based on the P&M permeability evolution model. The results showed that E decreases linearly with the increase of water saturation, while v increases linearly, and the change rate was affected by the fracture of coal and stress. The existence of fractures makes the mechanical properties of coal show great heterogeneity, resulting in the reduction of water action, and the stress will close the fractures to be as a whole, more prone to elastic deformation and greater deformation. The change of E and v will lead to a decrease of permeability faster or slower, which depends on the initial E and v and their change rate. Because the effects of E and v on permeability are different and nonlinear, the control effects of E and v on permeability are also different, depending on the E and v value. The quantitative numerical analysis showed that the variation of E can increase permeability change range by at least 32%. When the E is less than 3000 MPa and greater than 4000 MPa, the influence degree is greater, more than 60%, which means that the change of E has a significant control effect on permeability change. The change of v has little effect on the permeability change range with the maximum permeability change range is only 31%. The permeability of coal reservoir generally exceeds 3000 MPa, which means that more attention should be paid to the influence of E and v change with water production on permeability, especially the change of E.

Simulating the effect of salinity and kaolinite concentration on low salinity water flooding in sandstone reservoir of Sabah Basin

Low salinity waterflooding (LSWF) is a technique that involves injection of water at low salinity to improve oil recovery of matured oilfields. The primary objective of this study is to determine the effects of LSWF at different salinity in sandstone reservoirs on oil recovery and to simulate the effect of rock hysteresis on oil recovery. Reservoir simulation softwares ECLIPSE 100 and Petrel were utilized to simulate low salinity waterflooding in sandstone reservoir of the Sabah Basin. This study considers salinities from 100 up to 500 ppm (parts per million) at 1100 STB/day and 500 psi bottom-hole pressure. The results revealed that the highest oil recovery was 17.78 MMSTB at 100 ppm, while the lowest was 17.00 MMSTB at 500 ppm. This demonstrates that lower salinity water result in higher oil recovery. The difference in eventual recovery is not substantial when compared to the rate of recovery. Additionally, there is a strong link between incremental oil recovery and kaolinite content as well as the compaction and sand production. Oil is indirectly mobilised because of the clay particle composition. In addition, compaction causes an increase in residual oil saturation and irreversible water saturation. Furthermore, the larger the amount of kaolinite clay, the more oil may be extracted progressively.

Vertical differentiation of pedogenic iron forms – a key of hydromorphic soil profile development

This paper focuses on the vertical distribution and characterisation of pedogenic iron forms in a Gleysol- Histosol transect developed in a marshy area in the Danube-Tisza Interfluve, Hungary. Four soil profiles were investigated along a series of increasing waterlogging and spatial and temporal patterns of hydromorphic pedofeatures (characteristics of pedogenic iron forms) were recorded. Frequent and wide-range redox potential (Eh) changes caused the emergence of many types of redoximorphic iron features, including mottles, plaques and nodules. The forms of these features depended on the micro-environments determined by the vertical position in the soil profile and the presence of plant roots. The greatest iron enrichment occurred in the zone of most intensive and widest-range redox fluctuations. Increasing water saturation resulted the extension of gleyic pattern due to the existence of permanent reduction. Most of the features also showed annual variations during the varying periods of water saturation and aeration.

Calculation Model of Relative Permeability in Tight Sandstone Gas Reservoir with Stress Sensitivity

During the development of tight gas reservoir, the irreducible water saturation, rock permeability, and relative permeability change with formation pressure, which has a significant impact on well production. Based on capillary bundle model and fractal theory, the irreducible water saturation model, permeability model, and relative permeability model are constructed considering the influence of water film and stress sensitivity at the same time. The accuracy of this model is verified by results of nuclear magnetic experiment and comparison with previous models. The effects of some factors on irreducible water saturation, permeability, and relative permeability curves are discussed. The results show that the stress sensitivity will obviously reduce the formation permeability and increase the irreducible water saturation, and the existence of water film will reduce the permeability of gas phase. The increase of elastic modulus weakens the stress sensitivity of reservoir. The irreducible water saturation increases, and the relative permeability curve changes little with the increase of effective stress. When the minimum pore radius is constant, the ratio of maximum pore radius to minimum pore radius increases, the permeability increases, the irreducible water saturation decreases obviously, and the two-phase flow interval of relative permeability curve increases. When the displacement pressure increases, the irreducible water saturation decreases, and the interval of two-phase flow increases. These models can calculate the irreducible water saturation, permeability and relative permeability curves under any pressure in the development of tight gas reservoir. The findings of this study can help for better understanding of the productivity evaluation and performance prediction of tight sandstone gas reservoirs.

Experimental Study on the Mechanical Behavior of Coal Samples during Water Saturation.

When mining-induced fractures reach overlying aquifers, water enters the mining area and the coal is under different natural water saturation conditions, which significantly affect the mechanical behavior of the coal. In this study, uniaxial compression tests were conducted on dry, partially saturated, quasi-saturated, and fully saturated coal samples. The mechanical parameters, acoustic emission (AE) activities, and failure patterns of differently saturated coal samples were analyzed. The effect of water content on the behavior of coal and suggestions to ensure safe underground coal mining were discussed. The results indicate that the water content in coal increases nonlinearly with intrusion time and can be regarded as a logarithmic function. With increasing water saturation, the mechanical strength of the coal decreases on the whole and the AE activities, crack development, and burst severity are weakened significantly. The failure pattern of the coal samples changes from a dynamic type to a quasi-static one and from a compressive-shear type to a tensile one. Water content has four main effects on the mechanical behavior of the coal samples. These are a liquid bridge force, a water softening effect, a wedge effect, and a lubrication effect. With increasing water saturation, the effect of water gradually increases and predominates the coal failure, leading to a continuous decline in the strength of the coal samples. When the coal around the mining space is subjected to water, the high degree of water saturation in the coal decreases the risks of coal bursts significantly; however, it causes a large deformation and instability of the roadways. To ensure safe mining, more measures should be taken to decrease the amount of inrushing water, reduce the stress, and reinforce the anchor bolting support.