Search

Inhalable coal dust poses a serious threat to coal mining safety, air quality, and the health of miners. Therefore, the development of efficient dust suppressants is crucial for addressing this issue. This study evaluated the ability of three high-surface-active OPEO-type nonionic surfactants (OP4, OP9, and OP13) to improve the wetting properties of anthracite via extensive experiments and a molecular simulation and determined the micro-mechanism of different wetting properties. The surface tension results show that OP4 has the lowest surface tension (27.182 mN/m). Contact angle tests and wetting kinetics models suggest that OP4 exhibits the strongest wetting improvement ability on raw coal with the smallest contact angle (20.1°) and the fastest wetting rate. In addition, FTIR and XPS experimental results also reveal that OP4-treated coal surfaces introduce the most hydrophilic elements and groups. UV spectroscopy testing shows that OP4 has the highest adsorption capacity on the coal surface, reaching 133.45 mg/g. The surfactant is adsorbed on the surface and pores of anthracite, while the strong adsorption ability of OP4 results in the least amount of N2 adsorption (8.408 cm3/g) but the largest specific surface area (1.673 m2/g). In addition, the filling behavior and aggregation behavior of surfactants on the anthracite coal surface were observed using SEM. The MD simulation results indicate that OPEO reagents with overly long hydrophilic chains would produce spatial effects on the coal surface. Under the influence of the π-π interaction between the hydrophobic benzene ring and the coal surface, OPEO reagents with fewer ethylene oxide quantities are more prone to adsorb onto the coal surface. Therefore, after the adsorption of OP4, both the polarity and the water molecule adhesion ability of the coal surface are greatly enhanced, which helps to suppress dust production. These results provide important references and a foundation for future designs of efficient compound dust suppressant systems.

Fractional order theory was used to characterize the accelerated creep phase of a nonlinear creep model. To accurately describe each stage of the anthracite creep model, the “gyroscope” unit was introduced by combining the Heaviside function and the creep damage definition. The effect of damage on anthracite creep was determined by designing and completing three-axis graded-separation loading creep tests on anthracite. The test curves were combined to classify anthracite into five stages: transient deformation, pseudo-acceleration, deceleration, isothermal, and acceleration creep. Each stage was combined with suitable components to form a combined fractional-order creep model. The one-dimensional equation of the state of the model was extended to three dimensions. The Levenberg–Marquardt optimization algorithm for fitting origin rheological curves was used to complete the fitting of the basic parameters. Finite differences were performed on the model equation of state, and a secondary development of a combined fractional-order creep model (NEG) was completed based on the built-in Burgers model in FLAC3D. A comparison of the numerical simulation results shows that the combined fractional-order creep model is important for accurately predicting the full creep stage of anthracite.

As the essential component of shale, clay minerals have a vital influence on the pore structure and the gas content of reservoirs. To investigate the compositional characteristics of coal-measure shale and its effects on pore structure, a total of thirteen Taiyuan formation shale samples were collected from the Qinshui Basin and were analyzed using a combination of X-ray diffraction analysis, X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy (FE-SEM), polarized optical microscopy, and field emission scanning electron microscopy. The results show that the principal minerals of the samples are quartz, kaolinite, and illite. Most of the kaolinite was an original terrigenous detrital material with low crystallinity and a low degree of ordering, whereas the illite was mainly composed of 1Md resulting from diagenesis. Clay minerals developed slits, irregularly-shaped or multisized pores during diagenesis, which can be classed into interlayered pores, intergranular pores, and microfractures. Eight micro-morphological forms of clay minerals were summarized based on FE-SEM observations, such as compacted, parallel, bent, tilted, mutually supporting structures, etc., which are mainly formed by the mechanical compaction of clay minerals with different sizes, shapes, and contact relationships. The diversity and complexity of the micro-morphological forms of clay minerals contribute to the strong heterogeneity, low porosity and high permeability anisotropy of shale.

To gain the insight into the nature of organic matter (OM) micro-nanometer pores and fractal features of coal-measure shale from the OM macromolecular evolution perspective, 28 Taiyuan formation shale samples are collected from Qinshui Basin and characterized with Rock-eval, Field emission scanning electron microscope (FE-SEM), low-pressure N 2 gas adsorption (Lp-N 2 GA) and Fourier transform infrared spectroscopy (FTIR). The results show that OM is in the high-over mature stage. Pore size ranges from 5.7 to 26.7 nm and pores less than 4 nm are dominant. Two pore fractal dimensions D 1 and D 2 are obtained from Lp-N 2 GA with the Frenkel-Halsey-Hill method, which are in the range of 2.272-2.617 and 2.561-2.799, respectively. A series of FTIR structure parameters are obtained by peak fitting the FTIR spectra to describe the microstructure of OM molecules, such as length of aliphatic chain, degree of aromatic carbon condensation and hydrocarbon generation potential. Micro-nanometer OM-related pores in FE-SEM images can be classified as OM hydrocarbon-generating pores, OM structure pores, OM intergranular pores and micro- cracks, with the first being most developed. Both hydrocarbon-generation and condensation of aromatic nucleus have positive effects on D 1 . Hydrocarbon-generation is more effective for the development of micropores, while the condensation of aromatic nucleus is more conducive for the development of mesopores (

Understanding the adsorption/desorption behavior, as the primary phenomenon in shale reservoirs, is crucial for shale resource production, which is necessary in approximating the gas-in-place estim...

The Baikouquan Oilfield is entering middle and later periods of development. Casing failure, caused by the quality of cementing and casing corrosion, affects the normal production of the well. The number of wells in this situation has been increasing in recent years. Some wells with a high aquifer have no way to achieve effective plugging. The conventional measures have short validity periods and low plugging strengths. They cannot meet the requirements of subsequent fracturing operations and long-term production. Therefore, a new type of plugging agent with high strength, temperature resistance, salt resistance and micro-expansion features was designed and developed. The field test was carried out on four wells in the Baikouquan block, including three wells with a strong water-flooded layer and one well with an upper casing leakage point. A field test showed that the leakage formation was successfully plugged under the condition that the oilfield pressure test value was 30 MPa, with a 100% success rate. The average fluid volume decreases by 51.4%, and the average oil volume increases by 270.8%. The average daily oil volume per well increases by 3.2 t/d. The new plugging agent has the characteristics of no regurgitation, fast cementing speed with the new interface, high cementing strength and construction safety. The above advantages are of great significance in reducing the operation cost of oil and water well production and enhancing oil recovery.

CO2 injection has been recently proposed as an efficient method for oil recovery from shale reservoirs. However, significant amount of shale oil is still remaining in oil reservoirs after CO2 performance due to the reservoir heterogeneity and extremely low permeability. In this work, dimethyl ether is adopted as an additive in CO2 for enhancing shale oil recovery. The effect of dimethyl ether on the interfacial tension and viscosity of shale oil-CO2 systems are first measured. Using the low-field nuclear magnetic resonance (LFNMR) technique, dimethyl ether assisted CO2 injection is implemented on oil-saturated core samples to evaluate the performance of dimethyl ether as an additive in CO2 for shale oil extraction. Test results show that dimethyl ether decreases the interfacial tension of CO2-shale oil system more significantly compared to the traditional solvents, i.e., propane and n-butane. In addition, oil viscosity is more decreased when dimethyl ether is added. Based on the LFNMR tests, CO2 injection with the assistance of dimethyl ether is more efficient in recovering shale oil from the smaller pores, which is much higher than the traditional flooding scenarios, i.e., propane and n-butane assisted CO2 injection; dimethyl ether benefits to the solubility of CO2 in shale oil, which decreases the interfacial tension between CO2 and the in-situ oil and reduces oil viscosity at the same time. It enables a much higher shale oil recovery from the smaller pores. This study is expected to inspire new strategies that can be applied for shale oil reservoir development by adding cosolvents as an additive to CO2 for assisting CO2 injection.

CH4 and C2H6 are occupying components in shale gas. Determination of adsorption/desorption isotherms of CH4 and C2H6 on shale samples is significant for estimating the storage of shale resources in shale reservoirs. In this study, the thermogravimetric method is used to obtain the excess adsorption/desorption of CH4 and C2H6 on two typical shale samples. Simplified local density theory/Peng-Robinson equation of state (SLD-PR EOS) model is then applied to calculate the adsorbed density of CH4 and C2H6 on both shale samples, which is then applied to convert the measured excess adsorption into absolute adsorption values. Results show that C2H6 presents higher adsorption capacity than CH4 on shale samples, indicating the more affinity of C2H6 to the organic shale. Based on the predicted results from the SLD-PR EOS model, a reasonable agreement has been achieved with the measured adsorption isotherms, indicating the accuracy of the SLD-PR EOS model for predicting adsorption of CH4 and C2H6 on shale samples. In addition, the calculated adsorbed density of CH4 and C2H6 is a function of temperature and pressure, which agrees well with the results from the molecular simulations. The obtained absolute adsorption is always higher than the measured excess adsorption, emphasizing the importance of determination of adsorbed density in predicting the absolute adsorption of CH4 and C2H6 on shale. This study compares the adsorption/desorption behaviors of CH4 and C2H6 on typical shale samples, and more importantly, we propose a more efficient method, i.e., the SLD-PR EOS model, to calculate the absolute adsorption of CH4 and C2H6 on shale samples.