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Investigations of void distributions and formation mechanisms of proppant particles in closure fractures have extremely major significance for improving the production of coalbed methane. In this study, a numerical method was developed to simulate compaction processes of a proppant-filled fracture under different closure stresses. The particle trajectories, force chains and coordination numbers of proppants were extracted to analyze and investigate void ratio distributions and associated formation mechanisms. The results showed that during fracture closures from the top to bottom, some particles in the top layer of the proppant-filled fracture moved into the middle layer, which made the middle layer particles formed solid force-bearing structures. The greatest force was transmitted between particles in the middle layer. This was followed by particles in the top layer and finally, the bottom layer. In addition, the proportions of large coordination numbers, and average coordination numbers of the middle layer were the largest, followed by those of the top and bottom layers, which reflected that the particles of the middle layer were denser than those of the other two layers. The above factors caused the void ratios of the middle layer to be the lowest, followed by those of the top and bottom layer, respectively.

The internal stress levels of the crushed rock masses will change the movement states of the rock masses in the gob, and then affect the void distributions of crushed rock mass, and finally change the flow of gas in the gob. In this study, under the Lagrange framework, based on a discrete element method and a Hertz-Mindlin contact model, self-programming was used to simulate the compaction processes of a rock mass in mining gobs. The compression amounts were set as 0%, 5%, 10%, 15%, 20%, and 25%, respectively. The effects on the void distributions of the crushed rock masses of the internal stress levels of the crushed rock masses under the external load conditions were examined by changing the motion state of the rock blocks within in the gobs. The results showed that during the compression processes, the external loads could not be uniformly transmitted from the top of the crushed rock masses to the lower sections. Therefore the stress levels in the upper sections of the crashed rock masses were significantly higher than those of the lower sections. In addition, due to the rock blocks in the upper section of the crushed rock masses experiencing higher degrees of interference from the external forces, the sliding speeds of the upper rock blocks were also larger. At the same time, the rock blocks in the upper sections of the crushed rock masses tended to slide downward down longer. The migration of the rock blocks caused the upper rock blocks to become densely packed, and the coordination numbers of the rock blocks were large. However, the lower rock blocks were loosely distributed, and the coordination numbers of the rock blocks were small. This resulted in the void ratios in the lower sections of the crushed rock masses being higher than the void ratios in other layers of the crushed rock masses, with the void ratios of the lower sections of the rock masses determined to be 1.1–1.4 times that of the upper sections.

TiB2 nanoparticles reinforced AS41A alloys were fabricated by ultrasonic assisted stir casting. The influence of ultrasonic treatment and TiB2 nanoparticles on the microstructure and mechanical pro...

Peroxidase activity greatly impacts the maintenance of free radical homeostasis, and can prevent or treat diseases related to free radicals. Microperoxidase-11(MP-11) is created via hydrolysis of cytochrome c iron-porphyrin complexes. In these complexes, the heme iron is penta-coordinate with histidine and exhibits excellent antioxidant activity when decomposing hydrogen peroxide. In this study, we screened the Ph.D.-7 and Ph.D.-12 phage display peptide libraries and obtained ten small peptide ligands of deuterohemin(the vinyl groups of oxidized heme). Among these polypeptides, DhHP-7P1, 12P1, 12P2 and 12P6 have good enzymatic activity compared with MP-11, and exhibit activities up to 50% of MP-11. Based on the screened sequences, we designed a series of artificial microperoxidases and determined that a higher peroxidase activity could be achieved with an enzymatic active site containing a second site of histidine residue spaced between two arginine residues with an interval of two amino acids(Dh-XHRXXR).

Abandoned mine gobs contain a considerable amount of methane. Determining the methane flow space scientifically will directly affect the methane extraction of abandoned mine gobs. In this paper, a method is proposed to determine the gob methane flow space, based on the geological conditions of the Yongan abandoned mine in China. Physical simulation experiments were firstly conducted to simulate the abandoned gob formations. Subsequently, gas injection experiments were adopted to study the methane concentration distribution in the simulated gobs. The methane flow space was then determined based on the obtained methane concentration distribution. The results demonstrate that the methane flow space of abandoned mine gobs can be divided into four zones from the bottom to the top: methane high-concentration zone (MHZ), methane transition zone (MTZ), methane enrichment zone (MEZ) and methane no-stream zone (MNZ). The boundaries of these zones consistently exhibit a ‘V’ shape. The methane concentration in the MHZ is evidently higher than those in the MTZ and MEZ. The MTZ restrains the methane flow and causes a sharp decrease of the methane concentration in it. The methane in the MEZ is enriched as one shifts upwards and its concentration increases exponentially. Methane is absent in the MNZ. Based on these results, two surface vertical boreholes of the Yongan abandoned mine were selected to set their bottoms into the MEZ and MHZ, respectively. The field testing results demonstrate that the methane drainage flow rate at the bottom of the borehole located in the MHZ can increase by 1.5 times than that in the MEZ.

Hydraulic fracturing with proppants is the key technology in developing coalbed methane (CBM) reservoirs. However, coal fine retention in the fracturing proppant will directly affect its permeability and drop the CBM production. In this paper, coal fine retention experiments in fracturing proppants not containing coal fines, along with permeability tests of fracturing proppants containing coal fines, were successively conducted. The results showed that as the suspension concentrations of the coal fine increased, the coal fine retention amounts (Wr) of fracturing proppants increased monotonously, while the permeability decreased monotonously. Furthermore, as the suspension concentrations of the coal fines increased, the coal fine retention rate (Rr = Wr/Wt, where Wt represents the coal fine injected mass) first sharply increased monotonously to a peak level, and then slowly decreased monotonously. In addition, with the increases in the coal fine residue rates (Rcp = Wr/Wp, where Wp represents the mass of the proppants), the fracturing proppants permeability loss rates (η) were observed to first sharply increase and then slowly increase, indicating that the influences of the Wr on the permeability mainly occurred during the initial stage of the coal fines intrusions into the fracturing proppants. Furthermore, the relationship between the Rcp and η was also derived in this study as η = 0.71578 R cp 0.4575 .

Fracture closures have direct effects on the void ratio distributions of proppant particles filled in hydraulic fractures and then influence the fluid pathways of coalbed methane (CBM) within those fractures. In this paper, a numerical simulation method was used to investigate the void ratio distributions of proppant-filled fracture under different compression amounts of 0%, 5%, 10%, 15% and 20%. The results showed that the void ratio distributions had exhibited an inverted “U” shape, with a trend of decreasing first, followed by remaining constant, and then increasing from the bottom to the top of the fracture, which could be divided into three zones: bottom loose zone (BLZ), middle compaction zone (MCZ) and top loose zone (TLZ). At the same compression, the small coordination numbers in the BLZ and TLZ had accounted for a larger proportion, and the average coordination numbers and void ratios in the two zones were 0.8–0.9 and 1.3 times than those in the MCZ, respectively. In addition, the proportion of the large coordination numbers in the different layers had increased, and the layered average coordination numbers had increased linearly, which had resulted in the layered void ratios decreasing linearly with the increases in the compression amounts.