Effect of calcium lignosulfonate on the deformation and failure characteristics of cementing stone and its modification mechanism

In the coalbed methane extraction of surface wells in the mining area, the mining of coal seam in working face will cause a significant disturbance to overlying rock layer, which in turn will lead to the deformation and damage of surface wells. The coalbed methane extraction of surface wells in the mining-disturbed areas cannot be effectively performed. Cementing technology can effectively elongate the life span of mining-disturbed coalbed methane surface wells. As a critical factor of the cementing quality of surface wells, the early strength of the cement needs to meet the high cementing requirements. Cement stone is formed after cement consolidation. The mechanical properties of cement stone are of great importance to maintain the stability of mining-disturbed coalbed methane surface wells. It is an effective way to improve the cementing effect by adding dispersants to enhance the mechanical properties of cement stone. There are few researches on the deformation and failure characteristics of calcium lignosulfonate modified cement under the influence of mining disturbance. Uniaxial compression tests of calcium lignosulfonate modified cement with different mass fractions under cyclic loading were carried out to investigate the effect of calcium lignosulfonate on the deformation and failure characteristics of cement stone in mining-disturbed coalbed methane surface wells and its modification mechanism. The results show that the P-wave velocity and peak stress of cement stone increase first and then decrease with the increase of calcium lignosulfonate mass fraction, while the total acoustic emission ringing counts of cement decreases first and then increases with the increase of calcium lignosulfonate mass fraction. With the increase of the uniaxial cycle steps, the deformation modulus of cement stone shows a strengthening phenomenon, and the initial loading and unloading cycle has the most significant strengthening effect on the deformation modulus. With the addition of calcium lignosulfonate, the modified cement stone shows a tensile-dominated → shear-dominated → tensile-dominated combined damage modes. Besides, the fractal dimension of modified cement stone shows a trend of decrease before increase, indicating that the addition of the appropriate amount of calcium lignosulfonate can effectively improve the damage resistance of cement stone under uniaxial cyclic loading. With the increase of the mass fraction of calcium lignosulfonate, the pores between cement hydration products show a trend of decrease first and then increase. The addition of an appropriate amount of calcium lignosulfonate can promote the formation of abundant C−S−H gel and ettringite in cement, and the precipitates interweave on the surface of cement particles, which can significantly improve the peak stress of cement stone, and play a positive role in improving the mechanical properties of cement stone. Additionally, the porosity of cement stone decreases, which leads to the increase in the longitudinal wave velocity of cement stone and the decrease of cumulative acoustic emission ringing counts of the cement stone during cyclic loading. However, when the calcium lignosulfonate is excessively added, the air entraining and electrical repulsion of calcium lignosulfonate play a dominant role in the hydration process, which will introduce more bubbles, resulting in the occurrence of the gap between the cement particles, and the inhibition of the early formation of C−S−H gel and ettringite, which has a negative impact on the mechanical properties of cement stone. Furthermore, the porosity of cement stone increases, which leads to the decrease of the longitudinal wave velocity of cement stone and the increase of the cumulative acoustic emission ringing count of cement stone in the process of cyclic loading. Therefore, the influence of calcium lignosulfonate on the mechanical properties of cement stone has a double effect

Research status and reduction strategies of methane emissions from closed/abandoned coal mines

With the global transition to a low-carbon energy structure, coupled with the depletion of coal mine resources, gas disasters, and other problems, the number of closed/abandoned coal mines is increasing rapidly. After the coal mine closes, the residual methane in the goaf escapes to the ground continuously, becoming an essential source of greenhouse gas emissions. In view of a series of issues such as methane residual stock, emission rate and emission reduction measures in closed/abandoned coal mines, the number of closed/abandoned coal mines and the distribution of high-gas mines at home and abroad were clarified through a large number of literature review, and the sources and estimation methods of methane residual stock were summarized. At the same time, the theory and research method of methane geological leakage in the field of natural gas accumulation was used for reference, and the emission mechanism and monitoring means of residual methane were analyzed. Finally, the countermeasures and challenges of residual methane emission reduction were put forward. The study found that there are many closed/abandoned coal mines in Shanxi, Guizhou, Chongqing, Hunan, Jiangxi, etc., and the residual coal is mainly anthracite with strong methane adsorption capacity, resulting in a large amount of residual methane in the mine, which will become a critical methane emission source. Methane from closed/abandoned coal mines is desorbed and released to the goaf, and then discharged to the atmosphere through channels such as wellhead and mining-induced fractures. Methane monitoring in coal mines can be realized by means of satellite remote sensing, flux chamber method, geochemical probe method, micro-meteorological technology, etc. Based on the methane emission prediction model of closed/abandoned coal mines, the methane emissions from closed/abandoned coal mines may account for more than 20% of total methane emissions from coal mining operations by 2050, so it is urgent to solve the problem of methane emissions from closed/abandoned mines. Therefore, the countermeasures of emission reduction, such as extraction and utilization, in-situ deflagration power generation, microbial degradation of methane, water flooding, and methane emission channel closure are put forward. Considering the limitations of cost, treatment time, groundwater contamination, and other limitation factors, it is concluded the mineralized remediation method can be used to seal large-scale mining-induced fractures in overlying rocks, which can achieve the methane emission reduction goal of closed/abandoned coal mines at a low cost

Effect of naphthalene dispersant on the hydration kinetics of cement slurry: Nuclear magnetic resonance-based investigation

Cementing technology can effectively extend the life of coalbed methane surface drilling. The fluidity of the cement slurry during cementing is critical to the cementing quality. It is an effective way to improve the cementing quality by increasing the fluidity and pumping efficiency of cement paste by adding dispersants. In this paper, the effect of naphthalene dispersant on the hydration kinetics of G-grade cement was investigated by nuclear magnetic resonance. The results show that the increase of naphthalene dispersant mass fraction can effectively slow down the hydration of cement. The first relaxation peak of cement is correlated with its mobility, and the calculation of its peak index, area size, area share and combined action factor can be used to evaluate the retarding and dispersing effect of naphthalene dispersant on cement slurry more accurately. The main effects of naphthalene dispersant retarding and dispersing are: naphthalene dispersant causes an increase in ξ potential of cement particles, which makes the potential barrier overcome by cement particle coalescence rise; the sulfonic acid group of naphthalene dispersant can form a more stable complex with Ca2+, resulting in a reduced hydration rate. Naphthalene dispersant can decompose in cement into anions adsorbed on the surface of cement particles, forming a solvation film and producing a lubricating and dragging effect. The obtained research results provide theoretical support for the preparation and pumping of on-site cementing slurry from three aspects: the fluidity of the naphthalene dispersant modified cement slurry, the retarding effect and how to choose the pumping period

TFRC upregulation promotes ferroptosis in CVB3 infection via nucleus recruitment of Sp1

Abstract CVB3 is a single positive-strand enterovirus, and a common pathogen in myocarditis etiology. Although a number of antiviral candidates are under development, specific targeted therapy is not available for CVB3. Ferroptosis is a new type of regulatory cell death discovered in recent years. In this study, our team provided the first evidence that ferroptosis existed in CVB3 infection in vivo and in vitro by iron overload, and massive accumulation of lipid peroxides. Mechanistically, we construct a classical model of HeLa cells following a time-course infection (6, 12, 24, 36, 48 h) with CVB3 (MOI = 10). We demonstrated that the TFRC gene plays an important role in promoting ferroptosis in CVB3 infection and downregulation of TFRC attenuated the ferroptosis. Interestingly, we observed that TFRC was nuclear translocation induced by the CVB3, which was predominantly localized in the cell membrane, but redistributed to the nucleus during CVB3 infection. Moreover, we found that the transcription factor Sp1 was an essential factor that could bind to the TFRC promoter and upregulate the TFRC transcription. Collectively, these results suggest that the Sp1/TFRC/Fe axis may provide a new target for the development of therapies against CVB3 infection