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The microstructure, mineral composition, total organic carbon content, etc., of gas shale are crucial parameters for shale reservoirs, which can directly/indirectly affect shale brittleness, fracturing effect, adsorption ability and production efficiency. The study proposed a workflow to characterize the physical and mechanical parameters of Lower Silurian Longmaxi shale outcrop samples extracted from the favorable block in Changning, Sichuan, southwest China. This study elaborated on the influence of these physical and mechanical characteristics and proposed a corresponding brittleness index on shale extraction. In addition, it put forward corresponding suggestions for development and risk control. For a better understanding the mechanisms of shale gas storage and production, XRD, XRF, SEM, low temperature Nitrogen adsorption method, nuclear magnetic resonance and other measurements were employed to analyze and study the mineral composition, microstructure, and adsorption performance of shale. The results demonstrated that the pores of shale are mainly slit pores; there are diverse pore types in shale, mainly including intergranular pores, mineral particle dissolution pores, and internal pores of organic matter; The samples with relatively low porosity also noticeably exhibit ultra-low permeability, and the nanopore structure is remarkably significant, with distribution primarily in range of 5-237 nm. Finally, a brittleness index considering the influence of water content and the mechanical properties was proposed, and the coupling interaction of various minerals components and mechanical properties on the brittleness index can more objectively reflect the brittleness characteristics of deep shale formation. [ABSTRACT FROM AUTHOR]

The development of coalbed methane (CBM) in China is susceptible to the influence of microstructure. Therefore, it is crucial to understand the extension laws of hydraulic fractures and engineering responses in coal reservoirs affected by microstructure development. Utilizing the Dahebian block in western Guizhou as the study area, this investigation examines the coal reservoir characteristics, fracturing, and drainage engineering analysis of the well DC1 group in the region. The aim is to discuss the spatial distribution characteristics of hydraulic fractures, geological controlling factors influenced by microstructure, and their corresponding engineering responses. The results indicate that, for coal reservoirs unaffected by microstructure, the extension laws of the fracture network in both longitudinal and planar directions are influenced by burial depth and the regional stress field. In the microstructural belt, tectonic stress dominates, causing changes in the ground stress field. Consequently, the hydraulic fracture network deviates from the direction of the maximum principal stress during the extension process. When a secondary fracture is nearby, the hydraulic fracture network extends towards the shortest path radial secondary fracture direction, leading to a rapid increase in fracture width per unit length until it intersects with the secondary fracture. Additionally, the presence of secondary joints near the microfault structure decreases fracturing pressure and results in a dense distribution of the fracture network. This promotes the formation of a complex fracture network, favorable for fracturing. The extension of the fracture network in complex structural development areas is influenced by the microfault structure between wells, which is reflected in the fracturing construction pressure and fluid output. This accounts for the significant variations in the early drainage performance of CBM wells. [ABSTRACT FROM AUTHOR]

Loess is widely distributed in Northwestern China and serves as the preferred engineering construction material for anti-fouling barriers. Heavy metal contamination in soil presents significant challenges to the engineering safety of vulnerable loess structures. Hence, there is an urgent need to investigate the impact of heavy metal ions on their percolation performance. In order to investigate the effectiveness of microbially induced carbonate precipitation (MICP) using Sporosarcina pasturii (CGMCC1.3687) bacteria in reducing internal seepage erosion, a saturated permeability test was conducted on reshaped loess under constant water head saturation conditions. The response of loess to deionized water (DW) and ZnCl2 solution seepages was analyzed by monitoring changes in cation concentration over time, measuring Zeta potential, and using scanning electron microscopy (SEM). The results indicate that the hydrolysis of Zn2+ creates an acidic environment, leading to the dissolution of carbonate minerals in the loess, which enhances its permeability. The adsorption of Zn2+ ions and the resulting diffusion double-layer (DDL) effect reduce the thickness of the diffusion layer and increase the number of free water channels. Additionally, the permeability of loess exposed to ZnCl2 solution seepage significantly increased by 554.5% compared to loess exposed to deionized water (DW) seepage. Following the seepage of ZnCl2 solutions, changes in micropore area ratio were observed, decreasing by 48.80%, while mesopore areas increased by 23.9%. MICP treatment helps reduce erosion and volume shrinkage in contaminated loess. Carbonate precipitation enhances the erosion resistance of contaminated loess by absorbing or coating fine particles and creating bridging connections with coarse particles. These research results offer new perspectives on enhancing the seepage properties of saturated loess in the presence of heavy metal erosion and the geochemical mechanisms involved. [ABSTRACT FROM AUTHOR]

The Yungang Grottoes, one of China's most notable cultural heritage sites, are located in sandstone strata. The main causes of deterioration observed in the field are associated with moisture action, which greatly affects the long-term performance of the material. In particular, for immovable cultural heritage that is exposed to natural climatic fluctuations throughout the year, interaction with water vapor cannot be avoided. To obtain an insight into the water vapor transmission properties of local sandstone, a series of laboratory tests were conducted using the wet-cup method. The correlation of water vapor transmission with environmental relative humidity and pore structure was examined. The results indicate that as the relative humidity increased, the diffusion coefficient increased considerably due to the contribution of capillary condensate flow. In addition, a positive relationship was found between the diffusion coefficient and open porosity. The water vapor diffusion in sandstone occurred in transitory mode and the diffusion coefficient was estimated from the average pore radius. The calculated values were two orders of magnitude larger than those measured in the tests, reflecting the complex microstructural features concerning diffusion paths and area. The weathering processes constantly alter the sandstone's diffusion parameters, causing various damages in the Yungang Grottoes. [ABSTRACT FROM AUTHOR]

In the mudslide prone areas of western China, concrete piers were severely damaged by washing.In our previous research, the anti-abrasive UHPC prepared with saturated prewet high titanium heavy slag sand (ST-UHPC) is proposed to prevent such damage. And we studied the effect of grinding and erosion on the performance of ST-UHPC before, but the mechanism has not been studied in depth In order to study the microstructure evolution of ST-UHPC cement by the grinding and erosion, we use XRD, SEM, 27Al NMR, 29Si NMR test methods in this paper. By this way, we studied the effects of shock and salt erosion on hydration products composition, migration and transformation of Al-containing hydration products, hydration degree of cement and C-A-S-H gel microstructure. The results showed that the impact of bedload damaged the microstructure of UHPC. Then the damage of UHPC microstructure accelerates the transport of aggressive ions. Next, SO 4 2- erodes from the site of damage and produces expansive erosion products such as gypsum and calcareous vanadite. The erosion of SO 4 2- and Mg2+ resulted in the dealuminization and decalcification of C-A-S-H gel in UHPC cement and mechanical properties degradation. Thus, the expansion damage of UHPC and the impact damage of UHPC structure are aggravated. So the microstructure damage of UHPC was further aggravated. Under the action of impact, the water impacting material forms various chemical bonds with the C-A-S-H substrate. The chemical bonds results in the evolution of C-A-S-H microstructure. In conclusion, the structure of C-A-S-H substrate deteriorates obviously under the coupling effect of scouring and erosion. And the impact resistance of C-A-S-H substrate decreases significantly. • The anti-abrasive UHPC prepared with saturated prewet high titanium heavy slag sand was proposed. • XRD, SEM, 27Al NMR, 29Si NMR were used to study the microstructure evolution of ST-UHPC. • The microstructure evolution of UHPC was studied by molecular dynamics simulation. [ABSTRACT FROM AUTHOR]

To study the durability of magnesium oxychloride cement (MOC) in practical applications, samples from 6 to 80 years in different regions of China, including both north and south China, were collected. Phase composition and microstructure of MOC were analyzed, and phase transition patterns and microstructure characteristics of MOC were explored. The results show that, for MOC material, the main hydration product is 5Mg(OH)2·MgCl2·8H2O (phase 5·1·8), and the carbonation products are Mg(OH)2·MgCl2·2MgCO3·6H2O (phase 1·1·2·6) and 4MgCO3·Mg(OH)2·4H2O (phase 4·1·4). For MOC samples with ages less than 20 years, the content of phase 5·1·8 and the total content of carbonized phases (phase 1·1·2·6 and phase 4·1·4) increases and decreases in turn. The change of the total content of the carbonized phase is opposite to that of the phase 5·1·8 and is affected by phase 5·1·8. A calculation formula for the carbonation degree of MOC material system is proposed. The calculation results show that when the age is less than 14 years, the carbonation rate of MOC samples in the dry environment from north China is slow, but obviously increases when the age exceeds 14 years. Carbonation degree of the MOC samples at 6 years in the high humid environment of south China is close to that of the samples at about 20 years in north China. The crystal morphologies of different phases in MOC are varied. There are needle rod-like and flocculent crystals of phase 5·1·8 , short rod-like crystals of phase 1·1·2·6 , flaky crystals of phase 4·1·4 , and nubbly crystals of MgCO3 in MOC. Phase 5·1·8 ensures the integrity of the glass fiber, while sawdust shows disadvantages on the long-term service of MOC. [ABSTRACT FROM AUTHOR]