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In order to study the influence of moisture intrusion on crack propagation and failure mode of loaded coal, uniaxial compression tests and acoustic emission monitoring of coal with different moisture contents are carried out. The stress-strain characteristics, macroscopic failure patterns and change law of cumulative ringing counts of loaded coal with different moisture contents are compared and analyzed. The results of uniaxial compression tests show that with the increase of moisture content, the uniaxial compressive strength and elastic modulus of coal decrease continuously. The stress drop rate of coal gradually slows down in the post-peak stage. The macroscopic failure mode of coal samples changes from typical brittle failure to shear-tension combined failure. The acoustic emission monitoring results show that the cumulative ringing counts decreases with the increase of coal moisture content. The cumulative ringing counts curve's slope increases correspondingly, indicating that moisture intrusion can reduce the energy release when the coal cracks develop. However, the moisture intrusion aggravates the internal structure damage of coal. The results show that the water intrusion weakens the friction between crystal particles on the surface of cracks to some extent, and increases the possibility of coal sliding failure. At the same time, the water intrusion also reduces the surface active energy of the coal, resulting in a significant increase in the number of cracks generated during the loading process of the coal sample. This leads to a large drop in the macroscopic mechanical strength of the coal.

Enhanced coalbed methane (ECBM) recovery by gas injection is regarded as a feasible method for ECBM recovery. To investigate the mechanism of CH4 displacement by N2 injection, a series of physical experiments were conducted in the laboratory under different N2 injection pressures. The experimental results showed a continuous increase in the N2 volume fraction and a decrease in the CH4 volume fraction with the N2 injection pressure. The CH4 displacement efficiency increases rapidly in the initial stage and then gradually stabilizes. Given the effect of matrix shrinkage and effective stress on coal permeability, a dynamic multi‐field coupling model of ECBM recovery by N2 injection (N2‐ECBM) was proposed in this work. Then, numerical simulations were implemented by the coupling model to analyze the key factors affecting coal permeability, N2 injection pressure and CH4 pressure during the N2–ECBM process. Furthermore, the Response Surface Methodology (RSM) was used to investigate the interactions of multiple factors, the results reveal that an increase in one factor would weaken the influence of another factor. In addition, a RSM regression model was obtained and verified by the experimental data, with a well‐fitting outcomes. Therefore, the RSM model can be used in practical engineering applications to optimize specific extraction parameters for ECBM recovery at minimum cost in a limited extraction period. [ABSTRACT FROM AUTHOR]

To better evaluate the spatial steering effect of directional perforation hydraulic fractures, evaluation indexes for the spatial steering effect are first proposed in this paper. Then, these indexes are used to quantitatively evaluate existing physical experimental results. Finally, with the help of RFPA 2D -Flow software, the influence of perforation length and azimuth on the spatial steering process of hydraulic fracture are quantitatively analysed using four evaluation indexes. It is shown by the results that the spatial deflection trajectory, deflection distance, deflection angle and initiation pressure of hydraulic fractures can be used as quantitative evaluation indexes for the spatial steering effect of hydraulic fractures. The deflection paths of directional perforation hydraulic fractures are basically the same. They all gradually deflect to the maximum horizontal principal stress direction from the perforation hole and finally represent a double-wing bending fracture. The deflection distance, deflection angle and initiation pressure of hydraulic fractures increase gradually with increasing perforation azimuth, and the sensitivity of the deflection angle to the perforation azimuth of hydraulic fractures also increases. With increasing perforation length, the deflection distance of hydraulic fractures increases gradually. However, the deflection angle and initiation pressure decrease gradually, as does the sensitivity.

According to the theory of plane mechanics involving the interaction of hydraulic and natural fractures, the law of hydraulic fracture propagation under the influence of natural fractures is verified using theoretical analysis and RFPA2D-Flow numerical simulation approaches. The shear and tensile failure mechanisms of rock are simultaneously considered. Furthermore, the effects of the approach angle, principal stress difference, tensile strength and length of the natural fracture, and elastic modulus and Poisson’s ratio of the reservoir on the propagation law of a hydraulic fracture are investigated. The following results are obtained: (1) The numerical results agree with the experimental data, indicating that the RFPA2D-Flow software can be used to examine the hydraulic fracture propagation process under the action of natural fractures. (2) In the case of a low principal stress difference and low approach angle, the hydraulic fracture likely causes shear failure along the tip of the natural fracture. However, under a high stress difference and high approach angle, the hydraulic fracture spreads directly through the natural fracture along the original direction. (3) When natural fractures with a low tensile strength encounter hydraulic fractures, the hydraulic fractures likely deviate and expand along the natural fractures. However, in the case of natural fractures with a high tensile strength, the natural fracture surface is closed, and the hydraulic fracture directly passes through the natural fracture, propagating along the direction of the maximum principal stress. (4) Under the same principal stress difference, a longer natural fracture corresponds to the easier initiation and expansion of a hydraulic fracture from the tip of the natural fracture. However, when the size of the natural fracture is small, the hydraulic fracture tends to propagate directly through the natural fracture. (5) A smaller elastic modulus and larger Poisson’s ratio of the reservoir result in a larger fracture initiation pressure. The presented findings can provide theoretical guidance regarding the hydraulic fracturing of reservoirs with natural fractures.

Whether a tensile failure fracture will penetrate a stratum is difficult to ascertain at present. In view of this, the method of similar simulation and field verification are used to carry out a systematic study. Similar simulations show that tensile failure fractures will penetrate the layered strata if the compressive stress is greater than the compressive strength. Theoretical analysis points out that whether the tensile failure fractures will penetrate the layered strata can be expressed by the value of criterion of interconnected vertical fractures and the compression-tension ratio. When the value of criterion of interconnected vertical fractures is greater than the compression-tension ratio, the layered strata will break. This criterion was qualitatively verified with a field test. The results of this paper are of great significance for the prevention of water inrush in coal mines, and it can also promote the understanding of the law of strata movement.

Permeability improvement of coal seams by hydraulic fracturing can promote desorption of coalbed methane. However, the water-block effect will restrain desorption of coalbed methane. Based on the essence of the physical adsorption of methane, competitive adsorption, substitution desorption, the capillary effect, and the Jamin effect are analyzed to study the effect of the critical moisture content and liquid water on methane adsorption and desorption. Simultaneously, the effects of the fluid pressure, fracturing fluid, fracturing time, pore pressure, and other variables on methane adsorption and desorption characteristics are analyzed. Then, problems that require further study are described. [ABSTRACT FROM AUTHOR]

In the tunneling of frozen soil section of shaft sinking by freezing method, the traditional air pick excavation has large consumption of pick and drill rod, low excavation efficiency, and high labor intensity. The drilling explosive blasting method has a poor working environment and potential safety hazards. The safe and efficient excavation of frozen soil section is a difficult problem faced by freezing method shaft sinking. In this paper, a directional fracturing method by liquid CO2 phase change for freezing shaft sinking is proposed. Based on the traditional CO2 phase change fracturing device, a liquid CO2 phase change fracturing device with directional function is designed. It can not only fully crush and weaken the frozen soil in the shaft, but also can not disturb the shaft wall structure. The liquid CO2 phase change directional fracturing technology is firstly applied to the assisted tunneling in freezing shaft sinking. The field test results indicate that the directional liquid CO2 phase change generator has a good directional fracturing function. There are many obvious cracks formed around the directional fracture drilling hole, and the cracks are all extending toward the center of the protection circle. The angle between the two outermost cracks is close to the phase angle of directional discharge hole of liquid CO2 phase change generator. According to the statistics of field construction, the average daily excavation speed of frozen soil section is increased from 1.67 m/d to 2.45 m/d after directional fracturing by phase change of liquid CO2. Compared with explosive blasting weakening, liquid CO2 phase change fracturing has the advantages of no spark in the phase transformation process, easy control of pressure, convenient storage and transportation, simple operation, and relatively safe construction process. Liquid CO2 phase change fracturing shows a good application prospect in some fields which have high safety requirements. It is expected to be popularized and applied in slope excavation, tunnel chamber excavation, and other fields in the future. [ABSTRACT FROM AUTHOR]

A rapid, highly specific and sensitive UPLC-MS/MS method was developed for the determination of Quetiapine Fumarate, a therapeutic drug for various psychiatric disorders, in human plasma. The samples were pretreated using a protein precipitation method, followed by chromatographic separation using a column (Kinetex C18, 2.6µm 50*2.1mm) equipped with an ESI source and MRM mode mass spectrometer. In the validation results of the method, the analyte quetiapine showed a peak at approximately 1.0 minute and exhibited good linearity within the concentration from 2.5 to 2000ng/mL. The intra- and inter-batch precision CV% were within the range of -1.3% to 7.7% and precision of intra- and inter-batch were below 15.0%. Furthermore, this method demonstrated low matrix effects and high recovery rates. The quetiapine plasma sample solution remained stable at room temperature for 25 hours and following 4 freeze-thaw cycles. The prepared samples remained stable in the autosampler (The temperature control of the autosampler was 5 o C) for 185 hours and after four freeze-thaw cycles at -20 o C and -70 o C for 40 days. The present work effectively employed this approach to investigate the pharmacokinetics of orally administered quetiapine fumarate tablets in a cohort of healthy Chinese individuals, both in a fasting state and after a meal.