A novel approach to enhance wellbore stability was put forth, based on the wellbore rock properties and instability mechanism of the hydrate reservoir, given the issue of wellbore instability when using water-based drilling fluids (WBDFs) in drilling operations, in weakly cemented muddy fine silt reservoirs of natural gas hydrates in the South China Sea. Three main strategies were used to increase the stability of reservoirs: enhancing the underwater connection between sandstone particles and clay minerals, preventing clay hydration from spreading and expanding, and strengthening the stability of hydration skeleton structure. An appropriate drilling fluid system was built with soil phase containing wellbore stabilizer. Sulfonic acid groups and electrostatic interaction were introduced based on the characteristics of underwater adhesion of mussels. Through the process of free radical polymerization, a zwitterionic polymer containing catechol groups named DAAT was prepared for application in natural gas hydrate reservoir drilling. DAAT is composed of tannic acid (TA), dimethyl diallyl chloride ammonium chloride (DMDAAC), 2-acrylamide-2-methylpropanesulfonic acid (AMPS) and acrylamide (AM). Experimental results from mechanical property testing reveal an adhesion force of up to 4206 nN between SiO2 and 5 wt % DAAT, demonstrating its ability to bind quartz sand particles effectively. The compressive strength and cohesion of the cores treated with DAAT increased by 58.33 wt % and 53.26 wt %, respectively, at -10 degrees C, compared with pure ice particle cores. This demonstrates DAAT can significantly enhance the compressive strength and cohesion of the core. Furthermore, the adhesion force between DAAT and hydrate particles reaches up to 344.4 mN/m, significantly improving the structural stability between hydrate particles. It demonstrates excellent adhesive properties to hydrate particles. In addition to adsorbing clay minerals, rocks, and hydrate particles, DAAT also forms hydrogen bonds with argillaceous fine silt particles with its low temperature cohesiveness characteristic. As a result, it improves the cohesion between core particles, and enhances the adhesion between hydrates and rocks, thereby enhancing the stability of hydrate reservoirs. In summary, DAAT is characterized by a simple preparation process, cost-effectiveness, and environmental friendliness. It is an innovative and practical material for enhancing wellbore stability in WBDFs for natural gas hydrate exploration in the South China Sea.

In this study, ground granulated blast-furnace slag (GGBS) and fly ash (FA) were used as binders, while NaOH (NH) and Na2SiO3 (NS) served as alkali activators. Seawater (SW) was used instead of freshwater (FW) to develop a SW-GGBS-FA geopolymer for solidifying sandy soils. Geopolymer mortar specimens were tested for unconfined compressive strength (UCS) after being curing at room temperature. The results showed that the early strength of the seawater group specimens increased slowly less than that of the freshwater group specimens, while the late strength was 1.16 times higher than that of the freshwater group specimens. Factors including seawater salinity (SS), the GGBS/FA ratio, curing agent (CA) content, and the NH/ NS ratio were examined in this experiment. The results showed that the strength of the specimens was higher for SS of 1.2 %, G90:F10, CA content of 15 %, activator content was 15 %, and NH: NS of 50:50. The pore structure of the mortar specimens was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and computerized tomography (CT), revealing the mechanisms by which various factors influenced the microstructure. XRD indicated that SW-GGBS-FA geopolymer mortar newly produced Friedel salt and calcium silicate sulfate hydrate (C-S-S-H). The microstructures observed by CT and SEM showed that the pore radius of the seawater specimens was mainly less than 10 mu m, and the maximum crack length was 92.55 mu m. The pore radius of freshwater specimens was larger than that of seawater specimens, and the largest crack was 148.44 mu m, which confirmed that Friedel salt and C-S-S-H fill the pores and increase the UCS of the specimens.

In-depth research on the mechanical properties and constitutive models of gas hydrate-bearing sediments (GHBSs) is fundamental for achieving efficient hydrate exploration and geological disaster prevention. In the current study, a bounding surface model for GHBSs is developed based on the principle of thermodynamics. By choosing an appropriate dissipation function and free energy function, a yield surface function containing three shape parameters can be obtained. Considering the filling and bonding effects of hydrates, and introducing the hydrate strength evolution parameter, a thermodynamics-based bounding surface model for GHBSs is established using a non-associated flow rule. Then, the explicit substeping scheme with error control is implemented to develop a UMAT subroutine for the proposed model and integrated into the ABAQUS. Compared with the drained monotonic triaxial shear data indicates that the proposed model can adequately capture the shear behaviors of sandy, silty sandy, and clay-silty GHBSs under different stress levels and saturations. In addition, the model demonstrates good applicability and feasibility in undrained cyclic triaxial shear tests and boundary value problem analysis.

Shear strength of hydrate-bearing sediment is an essential parameter for assessing landslide potential of hydrate reservoirs under exploration conditions. However, the characteristics and simulation of this shear strength under varying dissociation conditions have not been thoroughly investigated. To this end, a series of triaxial compression tests were first carried out on sediments with varying initial hydrate saturations along dissociation pathways. Combining measured data with microscale analysis, the underlying mechanism for the evolution of shear strength in hydrate-bearing sediment was studied under varying partial dissociation pathways. Moreover, a shear strength model for hydrate-bearing sediment was proposed, taking into account the hydrate saturation and the unhydrated water content. Apart from the parameters derived from the hydrate characteristic curve, only one additional model parameter is required. The proposed model was validated using measured data on hydrate sediments. The results indicate that the proposed model can effectively capture the shear strength behavior of hydrate-bearing sediment under varying dissociation paths. Finally, a sensitivity analysis of the model parameters was conducted to characterize the proposed model. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Drought significantly reduces cotton boll yields across various fruiting branches (FBs). Potassium (K) application can partially mitigate the drought-induced damage by modifying the biosynthesis of photoassimilates in the leaf subtending to cotton boll (LSCB) and facilitating their transport to the subtending bolls, although its effects vary among FBs. The underlying mechanisms remain unclear. To investigate this, potting experiments were conducted at three soil relative water content (SRWC): 75 +/- 5 % (W75), 60 +/- 5 % (W60), and 45 +/- 5 % (W45), along with K rates of 0 (K0), 150 (K150) and 300 (K300) kg K2O ha-1. Compared to W75, the W60 and W45 treatments reduced the photosynthesis of LSCBs in different FBs, adversely affecting carbohydrate accumulation in the subtending cotton bolls. K application can mitigate this negative impact, with the most pronounced effects observed in the middle and upper FBs. K application (K150 and K300) enhanced the net photosynthetic rate, stomatal conductance, maximum mass yield of PSII and chlorophyll content of LSCB in the middle and upper FBs compared to K0 under drought conditions. Additionally, K application significantly increased K content in LSCBs within the middle and upper FBs, which in turn elevated sucrose phosphate synthase (SPS), and sucrose synthase (SuSy) activities, reducing the conversion of sucrose into starch, ultimately facilitating carbohydrate exports to the subtending bolls. In summary, we propose a model that elucidates how K application mitigates drought damage by enhancing the exports of photoassimilates from the middle and upper FBs to their respective subtending cotton bolls.

Sandy hydrate reservoirs are considered an ideal target for the extraction of marine natural gas hydrates (NGH). However, engineering geological risks, including reservoir sand production and seabed subsidence during the extraction process, present a significant challenge. In 2019, China discovered a high-concentration sandy NGH reservoir with favorable commercial development potential in the Qiongdongnan Basin of the South China Sea, establishing the region as a key focus for future exploration and development efforts. A thorough comprehension of macro-meso mechanical properties of this specific sandy NGH reservoir is essential for the safe and efficient extraction of hydrates. In this study, a novel method is proposed to calculate hydrate saturation of hydrate-bearing sandy sediments (HBSS) with hexagonal close-packed state. A series of undrained biaxial compression with flexible boundary show that hydrate cementation enhances the strength of the sample. However, an excessively high hydrate saturation is likely to induce strain softening, whereas an increase in confining pressure helps to mitigate strain softening. Hydrate cementation promotes the formation of abundant force chains. The inhomogeneous displacement, sliding, and relative rotation of the particles are the primary factors contributing to the formation of X-shaped shear bands, which is related to cemented bond breakage. The primary cause of hydrate cementation failure is tensile stress failure. External loading induces force chains to undergo buckling, fracturing, and restructuring, which governs fabric development. The research outcomes offer novel insights into the inhomogeneous deformation and macro-meso mechanical properties of HBSS at the particle-scale.

The use of nanoparticles has emerged as a popular amendment and promising approach to enhance plant resilience to environmental stressors, including salinity. Salinity stress is a critical issue in global agriculture, requiring strategies such as salt-tolerant crop varieties, soil amendments, and nanotechnology-based solutions to mitigate its effects. Therefore, this paper explores the role of plant-based titanium dioxide nanoparticles (nTiO2) in mitigating the effects of salinity stress on soybean phenotypic variation, water content, non-enzymatic antioxidants, malondialdehyde (MDA) and mineral contents. Both 0 and 30 ppm nTiO2 treatments were applied to the soybean plants, along with six salt concentrations (0, 25, 50, 100, 150, and 200 mM NaCl) and the combined effect of nTiO2 and salinity. Salinity decreased water content, chlorophyll and carotenoids which results in a significant decrement in the total fresh and dry weights. Treatment of control and NaCl treated plants by nTiO2 showed improvements in the vegetative growth of soybean plants by increasing its chlorophyll, water content and carbohydrates. Additionally, nTiO2 application boosted the accumulation of non-enzymatic antioxidants, contributing to reduced oxidative damage (less MDA). Notably, it also mitigated Na+ accumulation while promoting K+ and Mg++ uptake in both leaves and roots, essential for maintaining ion homeostasis and metabolic function. These results suggest that nTiO2 has the potential to improve salinity tolerance in soybean by maintaining proper ion balance and reducing MDA level, offering a promising strategy for crop management in saline-prone areas.

This paper employs the discrete element method (DEM) to simulate the nanoindentation creep of calcium- silicate-hydrate (C-S-H), focusing on indentation deformation, particle interactions, and stress transmission paths. The Rate Process Theory (RPT), previously utilized in the creep modeling of cohesive soils and other granular materials, is proposed to simulate C-S-H creep. Due to the nanometer size of C-S-H particles, the critical time step in DEM simulations is very small. Therefore, a time-scaling algorithm is used to match the DEM simulation time with the physical time in laboratory tests, accelerating the simulation time by a factor of 1 x 108. C-S-H particle assemblies with specific packing densities are generated using Particle Flow Code (PFC3D, version 5.0), with coordination numbers and cohesion forces controlled by the stress-servo of PFC walls. Virtual nano- indentations using a Berkovich indenter are conducted on C-S-H particle assemblies with three different packing densities (0.74, 0.64, and 0.58), followed by parameters calibration. Results show that the DEM + RPT method can capture the scaling relations between the indentation modulus, hardness, and contact creep modulus of C-S- H particle assemblies and the packing density. Furthermore, DEM simulations reveal particle rearrangement under Berkovich and flat-tip indenters, highlighting that different indenter types lead to distinct creep kinetics in C-S-H, with the Berkovich indenters experimentally capturing long-term creep and flat-tip indenters measuring short-term creep.

In the long-term exploitation of natural gas hydrate, the stress change intensifies the creep effect and leads to the destruction of pore structures, which makes it difficult to predict the permeability of hydrate reservoir. Although permeability is crucial to optimize gas recovery for gas hydrate reservoirs, until now, accurately modeling the permeability of hydrate-bearing clayey-silty sediments during the creep process remains a significant challenge. In this study, by combining the nonlinear fractional-order constitutive model and the Kozeny-Carman (KC) equation, a novel creep model for predicting the permeability of hydrate-bearing clayey-silty sediments has been proposed. In addition, experimental tests have been conducted to validate the derived model. The proposed model is further validated against other available test data. When the yield function F 0, the penetrating damage bands will be generated. Results show that, once the model parameters are determined appropriately by fitting the test data, the model can also be used to predict permeability under any other stress conditions. This study has a certain guiding significance for elucidating the permeability evolution mechanisms of hydrate-bearing clayey-silty sediments during the extraction of marine gas hydrates. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Currently, traditional vertical barrier materials are associated with large carbon footprints and high costs (in some regions) due to the widespread use of Portland cement and sodium-based bentonite materials. In recent years, a new technology of Carbonized Reactive Magnesia Cement (CRMC) has gradually been developed to sequester CO2 using Eco-cement. The application prospects of CRMC in vertical barrier materials are explored in this study. The changes in flowability of Reactive Magnesia Cement (RMC) slurry and the unconfined compressive strengthen (UCS) and permeability characteristics of CRMC treated soils are investigated. The results show that the fluidity of RMC slurry decreases further with the increase of MgO substitute cement content. For RMC slurry meeting the fluidity requirements, UCS increased rapidly in the early period (3 h) after carbonization, reaching 348.33 kPa, and the hydraulic conductivity k decreased (k < 1 x10(- 7) cm/s) in the later period (14d), and the final hydraulic conductivity reached 6.13 x 10(- 8) cm/s (28d). The pores of the material are filled with a large number of hydration products and carbonates, which alters the pore size distribution structure of the material. This is the reason for the mechanical properties and permeability performance of CRMC treated soils. The overall results of this study well demonstrate that CRMC treated soils, as a new, environmentally friendly, and cost-effective material, have great potential in the construction of vertical barriers.