Search Results (412)

Rough surfaces known as stylolites are common geological features that are developed by pressure solution, especially in carbonate rocks, where they are used as strain markers and as stress gauges. As applications are developing in various geological settings, questions arise regarding the uncertainties associated with quantitative estimates of paleostress using stylolite roughness. This contribution reports for the first time a measurement of the temperature at which pressure solution was active by applying clumped isotopes thermometry to calcite cement found in jogs linking the tips of the stylolites. This authigenic calcite formed as a redistribution of the surrounding dissolved material by the same dissolution processes that formed the extensive stylolite network. We compare the depth derived from these temperatures to the depth calculated from the vertical stress inversion of a bedding parallel stylolite population documented on a slab of the Calcare Massiccio formation (early Jurassic) formerly collected in the Umbria-Marches Arcuate Ridge (Northern Apennines, Italy). We further validate the coevality between the jog development and the pressure solution by simulating the stress field around the stylolite tip. Calcite clumped isotopes constrain crystallization to temperatures between 35 and 40 °C from a common fluid with a δ¹⁸O signature around −1.3‰ SMOW. Additional δ¹⁸O isotopes on numerous jogs allows the range of precipitation temperature to be extended to from 25 to 53 °C, corresponding to a depth range of 650 to 1900 m. This may be directly compared to the results of stylolite roughness inversion for stress, which predict a range of vertical stress from 14 to 46 MPa, corresponding to depths from 400 to 2000 m. The overall correlation between these two independent depth estimates suggests that sedimentary stylolites can reliably be used as a depth gauge, independently of the thermal gradient. Beyond the method validation, our study also reveals some mechanisms of pressure solution and the associated p,T conditions favouring their development in carbonates. Full article

Water pipelines in water diversion projects can leak, leading to soil deformation and ground subsidence, necessitating research into soil deformation monitoring technology. This study conducted model tests to monitor soil deformation around leaking buried water pipelines using distributed fiber optic strain sensing (DFOSS) technology based on optical frequency domain reflectometry (OFDR). By arranging strain measurement fibers in a pipe–soil model, we investigated how leak location, leak size, pipe burial depth, and water flow velocity affect soil strain field monitoring results. The results showed that pipeline leakage creates a “saddle-shaped” spatial distribution of soil strain above the pipeline, effectively indicating ground subsidence locations. When only one survey line is arranged, it is preferable to place the optical fiber directly above the pipeline. Surface monitoring fibers primarily detected tensile strain, with more pronounced peak values observed under conditions of larger leak size, higher flow velocity, shallow burial depth, and top-pipe leakage location. Monitoring fibers below the pipeline showed mainly unimodal distribution, with peak strain coinciding with the leak location. The sequential timing of strain changes at different fiber positions enabled the determination of soil seepage direction. This study demonstrates that DFOSS technology can provide important support for the early warning of such geological disasters. Full article

This paper proposes an analytical solution for the seepage field when a localized line leakage occurs in a tunnel by accurately considering the boundary conditions at the leakage site, which overcomes the problem of current methods, such as the equivalent method or methods improving on the existing analytical solution for fully drained tunnels, being unable to give an accurate analytical solution. First, the semi-infinite seepage region is converted into a rectangular seepage region using two conformal transformations. Subsequently, in order to accurately consider the boundary conditions at the leakage site, the rectangular seepage region with a discontinuous boundary is divided into three subregions with continuous boundaries, and the water head solution for each subregion is given by using the separated variable method. Finally, the principle of orthogonality of trigonometric functions is specially adopted to construct a non-homogeneous system of equations to solve the unknowns in the analytical solution, and through the inverse transformation of the conformal transformation, an analytical solution for the steady-state seepage field when localized line leakage occurs in a tunnel is obtained. The solution proposed is verified by its satisfactory agreement with the numerical simulation results and existing experimental results, and is much more accurate than the existing analytical solution. In addition, the proposed analytical solution is much less computationally demanding compared to numerical simulations. Finally, the capability of the proposed analytical solution is demonstrated by a parametric analysis of the tunnel burial depth, leakage location, and leakage width, and some meaningful conclusions are drawn. Full article

Revealing geological environment resilience (GER) under seawater intrusion (SWI) hazards is a prerequisite for solving groundwater resource depletion, land salinization, and ecological degradation in coastal cities. This study applies the resilience design approach based on urban complex adaptive systems theory to understand the impact of SWI on the geological environment. Taking SWI as the research object, the GER evaluation method under SWI disaster was established by selecting five elastic indexes: disturbance intensity, geological environment vulnerability, stress resistance, recovery, and adaptability. This method is used to evaluate the GER level of the coastal areas of Shenzhen in recent years under the impact of SWI hazards. The study found that there is a negative correlation between the intensity of disturbance and precipitation amount. The vulnerability is greater the closer the distance to the coastline and the shallower the depth of bedrock burial. Resistance is composed of early warning ability and disaster prevention ability, and the result is 10.07, which belongs to the medium level. The recovery is 1.49, which is at a relatively high level, indicating a high capacity for restoration ability. The adaptability increased from 3.03 to 3.13, so that the area of seawater intrusion is becoming smaller. GER is affected by precipitation amount and depth of bedrock burial; the greater the precipitation and the shallower the bedrock burial, the lower the GER. Precipitation amount significantly impacts the SWI situation in the eastern coastal area of Shenzhen. In the central region, the impact of precipitation on GER is less significant. However, in the western region, the depth of bedrock burial primarily affects GER. Compared to completely weathered granite, Pleistocene fluvial plain sediments are more susceptible to SWI effects in freshwater environments. This study contributes to a deeper understanding of the impact of SWI on the geological environment in coastal areas, providing decision-makers with the necessary knowledge to develop targeted and effective governance and prevention strategies. Full article

The microfracture and pore structure characteristics of coal reservoirs are crucial for coalbed methane (CBM) development. This study examines the evolution of pore and fracture structures at the microscopic level and their fractal characteristics, elucidating their impact on CBM development in the northern Guizhou coal reservoirs. The results indicate that the pores and fractures in the coal reservoirs are relatively well-developed, which facilitates the adsorption of CBM. The density of primary fractures ranges from 5.8 to 14.4 pcs/cm, while the density of secondary fractures ranges from 3.6 to 11.8 pcs/cm. As the metamorphic degree of coal increases, the density of primary fractures initially increases and then decreases, whereas the density of secondary fractures decreases with increasing metamorphic degree. With increasing vitrinite reflectance, the specific surface area and pore volume of the coal samples first decrease and then increase. The fractal dimension ranges from 2.3761 to 2.8361; as the vitrinite reflectance of the coal samples increases, the fractal dimension D₁ decreases initially and then increases, while D₂ decreases. In the northern Guizhou region, CBM is characterized by an enrichment model of “anticline dominance + fault-hydrogeological dual sealing” along with geological controlling factors of” burial depth controlling gas content and permeability + local fault controlling accumulation”. The research findings provide a theoretical basis for the occurrence and extraction of CBM in northern Guizhou. Full article

Burial depth can significantly impact the pore structure characteristics of shale. The Lower Silurian Longmaxi Shale in the Weiyuan block of the Sichuan Basin is a marine formation that we studied for deep shale gas exploration. We used two groups of Longmaxi samples, outcrop shale and middle-deep shale, to investigate the pore structure fractal features at varying burial depths using a combination of mineralogy, organic geochemistry, scanning electron microscopy (SEM), and low-temperature gas (CO₂, N₂) adsorption. The V-S fractal model was used to determine the fractal dimension (Dc) of micropores, and the FHH fractal model was used to determine the fractal dimension (D_N) of mesopores. The findings indicate that the pore morphology of organic matter becomes irregular and more broken as the burial depth increases, as does the content and maturity of organic matter. The pore size of organic matter gradually decreases, the SSA (BET, DR) and PV (BJH, DA) of shale pores increase, the pore structure becomes more complex, and the average shale pore size decreases. According to this study, the organic matter content and its maturity show an increasing trend as burial depth increases. Meanwhile, the organic matter’s pore morphology tends to be irregular, and fracture rates rise, which causes the organic matter’s pore size to gradually decrease. In addition, the SSA (comprising the values assessed by BET and DR techniques) and PV (evaluated by BJH and DA methods) of shale pores grew, suggesting that the pore structure became more complex. Correspondingly, the average pore size of the shale decreased. The fractal dimensions of the micropores (D_C), mesoporous surface (D_N1), and mesoporous structure (D_N2) of outcrop shale are 2.6728~2.7245, 2.5612~2.5838, and 2.7911~2.8042, respectively. The mean values are 2.6987, 2.5725, and 2.7977, respectively. The D_C, D_N1, and D_N2 of middle-deep shale are 2.6221~2.7510, 2.6085~2.6390, and 2.8140~2.8357, respectively, and the mean values are 2.7050, 2.6243, and 2.8277, respectively. As the fractal dimension grows, the shale’s pore structure becomes more intricate, and the heterogeneity increases as the buried depth increases. The fractal dimension has a positive association with the pore structure parameters (SSA, PV), TOC, and R_o and a negative association with the mineral component (quartz, feldspar, clay mineral) contents. Minerals like quartz, feldspar, and clay will slow down the expansion of pores, but when SSA and PV increase, the pore heterogeneity will be greater and the pore structure more complex. Full article

A field experiment was conducted on sunflowers in a mild-to-moderate saline–alkaline area in the Tumochuan Plain irrigation region in China. The experimental design included using surface drip irrigation as a control (CK) and four subsurface drip irrigation treatments at burial depths of 10 cm (D10), 15 cm (D15), 20 cm (D20), and 25 cm (D25) to analyze the effect of the drip irrigation belt burial depth on soil physicochemical properties and soil desalination in the main root zone of saline–alkaline sunflower farmland. Based on macro-genome sequencing technology, the diversity, composition, and structure of soil fungal communities in the main root zone were revealed in response to the depth of drip irrigation. The results show that subsurface drip irrigation treatments improved soil desalination with rates ranging from 15.33% to 26.96%. The D25 treatment achieved an 82.01% higher desalination rate than CK and outperformed D10, D15, and D20 by 43.35%, 13.43%, and 24.89%, respectively, demonstrating the most effective desalination with a 25 cm burial depth under the same water and fertilizer management conditions. Additionally, subsurface drip irrigation enhanced the diversity and abundance of soil fungal communities; the Shannon indices for D15 and D20 were 8.1% and 12.3% higher than that of CK, respectively, whereas the Chao1 indices increased by 21.2% and 17.4%, respectively. During the budding stage, the fungal community in the main root zone (20–40 cm) was dominated by Ascomycetes and Tephritobacterium, with Alternaria being the predominant genus. Notably, the relative abundance of Ascomycetes was 118.8% higher in D25 than in CK. Structural equation modeling quantified the relationships between soil physicochemical properties, with an SMC of 0.94, indicating a model fit within an acceptable range. An SEM analysis revealed that the soil water content (SWC), soil EC, and soil NO₃⁻-N exerted the most significant combined effect on soil fungal composition and diversity. This study examined the effects of the drip irrigation tape burial depth on soil physicochemical characteristics, the fungal community structure, and diversity in the main root zone (20–40 cm) of saline–alkaline sunflower fields under subsurface drip irrigation. This study aims to provide theoretical support for water-saving agricultural practices in saline–alkaline soils. We developed a subsurface drip irrigation method for sunflowers in the lightly to moderately saline–alkaline land in the irrigation area of China’s Tumochuan Plain, and the suitable depth of burial of the drip irrigation belt was 25 cm. Full article

In view of the deep burial depth, high formation pressure, and presence of top and bottom water in offshore extra-heavy-oil reservoirs, this paper conducts a study on the production performance and flow field variation law of steam huff-and-puff to steam flooding conversion in thick heavy-oil reservoirs based on physical simulation, and analyzes the development effect of the conversion from steam huff-and-puff to steam flooding. On this basis, by comprehensively considering the advantages of gravity-assisted steam flooding and a three-dimensional HHSD well pattern obtained from physical simulation experiments, this paper proposes a well pattern development mode of steam huff-and-puff to composite displacement and drainage, and analyzes the development effect of this well pattern mode using the reservoir numerical simulation method. The research results show that, compared with the planar well pattern of steam huff-and-puff to steam flooding conversion, the adoption of the three-dimensional well pattern can significantly improve the degree of reservoir production and the expansion dynamics of the steam chamber, and mitigate adverse effects such as the increase in water cut caused by top and bottom water on thermal recovery. The composite development of steam huff-and-puff to composite displacement and drainage can be divided into three stages: thermal communication, gravity drainage-assisted steam flooding, and thermal breakthrough erosion and oil washing. The steam chamber presents a development mode of “single-point development–rapid longitudinal expansion–rapid transverse expansion upon reaching the top–polymerization into a sheet”, and simultaneously possesses the oil displacement mechanisms of both steam displacement and gravity drainage. The proposed composite mode of steam huff-and-puff to composite displacement and drainage has guided the implementation of adjustment wells in the Bohai L Oilfield, and the recovery factor has been increased by about 20% compared with the steam huff-and-puff development of the basic well pattern. This study has reference and guiding significance for the efficient thermal recovery development of this oilfield. Full article

The tight reservoirs in the Sichuan Basin generally contain water and have complex gas–water relationships. The dynamic changes and main controlling factors of natural gas injection are unclear, which has had a serious impact on the exploration and development of tight sandstone gas. This article selects samples from Yongqian and Qiulin gas fields to characterize the reservoir characteristics of the tight sandstone samples in the Xu-3 section. Nuclear magnetic resonance technology is applied to plan gas–water injection simulation experiments, and the dynamic changes in pore water and gas content during the natural gas injection of tight reservoir rock samples are characterized. The main controlling factors are analyzed based on the theory of nuclear magnetic resonance singlet and multifractal models. The results showed that material composition, pore type, structural characteristics, and physical properties cooperatively control the charging characteristics of natural gas. There was no significant difference in mineral content among the tight sandstone samples, and the pore morphology types were mainly parallel plate-like pores and fracture-type pores. There were significant differences in the pore structure characteristics of the samples with varying burial depths. The heterogeneity of gas-bearing pores is negatively related to the buried depth of tight sandstone, is a coupling relationship with quartz and feldspar content, and is negatively correlated with pore permeability. The stronger the sample heterogeneity, the more unfavorable it is for natural gas migration and accumulation. Full article

Sonchus asper and S. oleraceus are among the most problematic broadleaf weeds in eastern cropping systems of Australia. This study investigated the seed germination ecology of S. asper and S. oleraceus. The study hypothesized that S. asper may have greater ecological advantages under adverse environmental conditions compared to S. oleraceus. Results showed that S. asper consistently outperformed S. oleraceus across different light regimes and stress conditions. At a lower temperature regime of 15/5 °C, seed germination of S. oleraceus decreased by 19% compared to S. asper. Germination of S. oleraceus significantly declined under dark conditions, while over 90% of S. asper seeds germinated under both light/dark and dark conditions. Under water stress (osmotic potential of −0.4 MPa), S. oleraceus germination dropped by 74% compared to S. asper, indicating S. asper’s superior drought tolerance. Both species exhibited moderate salinity tolerance (40 mM NaCl) to germinate, highlighting their potential to invade saline cropping environments. The burial study revealed that S. oleraceus had higher germination at the soil surface, but no germination occurred from 4 cm, while 23% of S. asper seeds still emerged from that depth. The burial depth required to inhibit 50% emergence of S. asper and S. oleraceus was 3.3 cm and 0.3 cm, respectively. These findings highlight S. asper’s greater adaptability to low temperatures, burial depth, and stress conditions than S. oleraceus. The insights from this study can inform agronomic strategies, including tillage depth and mulching, to mitigate the impact of these invasive species on Australian cropping systems. Full article

Deep coalbed methane (CBM) demonstrates significant production potential, and a fervent exploration and development boom is currently underway in China. The permeability of coal reservoirs is heavily influenced by pore–fracture structure heterogeneity. Some researches have been conducted on deep coals’ pore–fracture structure; however, these studies mostly consider coal as a homogeneous material, neglecting the heterogeneity of the macrolithotypes within the coal. In this study, 33 deep coals with burial depths of more than 2000 m were obtained from the Daning-Jixian block of the Ordos Basin, covering all macrolithotypes: bright coal (BC), semi-bright coal (SBC), semi-dull coal (SDC), and dull coal (DC). These samples were subjected to three sets of NMR tests in dry, fully saturated, and irreducible water conditions, with the pore–fracture structure characteristics being analyzed. The results demonstrate that the sampled deep coals’ pore–fracture structure is highly heterogeneous, with transitional pores being dominant, followed by mesopores, “macropores and fractures”, and micropores. The NMR T_2C ranges from 0.61 to 2.44 ms, with an average of 1.19 ms; a higher T_2C value indicates more developed micropores. The ranges for producible water porosity (φ_pr) and producible water saturation (S_pr) are 0.31–7.24% (avg. 2.42%) and 6.97–71.47% (avg. 31.06%), respectively. Both of them exhibit a high positive correlation with the total volumes of “macropores and fractures” and mesopores. Compared to SDC and DC, the BC and SBC, especially the former, overall contain more “macropores and fractures” and mesopores, fewer transitional pores and micropores, and higher φ_pr and S_pr. These findings suggest that regions with abundant BC and SBC should be prioritized during deep CBM exploration and production due to the inherently superior permeability and gas extraction potential of BC and SBC, and these coals are likely to require less intensive stimulation to achieve higher recovery rates and could provide more sustainable gas production over time. Full article

Underground compressed air energy storage chambers are a promising emerging energy storage technology with strict limitations relating to the stability of the surrounding rock. This study conducted displacement and plastic zone analyses during the excavation and stabilization phases of the chamber utilizing the finite difference method based on engineering data, demonstrating that the stability of salt rock can effectively withstand internal pressures ranging from 0 to 9 MPa, with an average of 15 mm in the Z-axis and 19.23 mm in the X-axis. To further investigate the feasibility of subterranean energy storage reservoirs, the FOS for various surrounding rocks was calculated at different burial depths. These results facilitated a parameter sensitivity analysis on the stability of the surrounding rock of the underground energy storage reservoir. The dynamic reaction of the underground chamber was studied using synthetic seismic wave technology, demonstrating that the seismic capacity of the structure adhered to the code, and the post-seismic displacement remained within the safe range (Z-axis 34 mm, horizontal 19 mm). The results demonstrate the stability analysis method of the chamber and establish a foundation for the extensive implementation of CAES which will contribute to the development of energy storage technology. Full article

The Fushan Depression is a hydrocarbon-rich depression in the Beibuwan Basin, South China Sea. In this study, 14 source rocks and 19 crude oils from the Chaoyang Step-Fault Zone and Southern Slope Zone were geochemically analyzed to determine their origins. The hydrocarbon generation, migration, and accumulation processes were also determined using two-dimensional basin modeling. Crude oils from the low-step area show a close relationship with the source rocks of the first and second members of the Eocene Liushagang Formation (Els₁ and Els₂). The oils from the middle-step area and the Southern Slope Zone are derived from the local source rocks in those areas, in the third member of the Eocene Liushagang Formation (Els₃). Hydrocarbons generated from the Els₃ source rocks of the Southern Slope Zone migrated along sand bodies to the Els₃ reservoir. The fault system of the Chaoyang Step-Fault Zone controls hydrocarbon migration and accumulation in the low-step and middle-step areas. The resource potential of the middle-step area is limited by its shallow burial depth. The low-step area is a more favorable exploration area due to its proximity to the source kitchen. Full article

Recent advancements in underground construction have led to the widespread utilization of pipe jacking. However, the engineering challenges posed by frozen ground in pipe jacking projects have not been extensively studied. This research aims to address the critical challenges linked to employing pipe jacking in frozen ground for underground construction. It is widely recognized that the accurate calculation of jacking thrust and mitigation of pipe–soil interaction plays a crucial role in determining the success or failure of pipe jacking operations. To explore these issues, this study conducted numerical simulations and comparative analyses, considering various factors such as soil properties, geometric dimensions, and burial depth, to assess their influence on jacking thrust. Additionally, the study also examines the freeze–thaw effect on concrete pipes and the injected lubricant. The results indicate that the numerical model, which considers the temperature effects and static friction instead of sliding friction, provides a more reliable estimation of jacking thrust in frozen ground compared to traditional theoretical models. Furthermore, the freezing point depression method was successfully employed in the development of an anti-freezing lubricant, which can effectively reduce pipe–soil interaction even at extremely low temperatures of up to −10 °C. Full article

This study proposes a buried PE gas pipeline positioning method based on the elliptical method of an acoustic signal analysis. The cross-correlation time delay positioning technology is combined with the elliptical equation, forming an effective mechanism for pipeline depth positioning. First, a dual-tree complex wavelet transform is employed to denoise the collected signals, enhancing the quality and accuracy of the data. Subsequently, the cross-correlation function is utilized to extract the delay times between the signals. The obtained delay times are then substituted into the elliptical equation to calculate the depth of the buried PE pipeline. Based on this theoretical framework, a simulation model is established in COMSOL, and positioning simulation analyses are conducted under three different conditions: pipeline depth, relative sensor positions, and distances between sensors and excitation points. The simulation results indicate that a clear correlation exists between the signal delay time and the pipeline position, with simulation errors controlled within 5%, thus validating the theoretical feasibility of the method. To further assess the effectiveness of this approach, an experimental testing system is constructed. The experimental study was carried out under four different conditions: pipeline burial depth, relative sensor positions, distances between sensors and excitation points, and excitation frequencies. The experimental results demonstrate that these factors significantly affect the pipeline depth positioning. The comparison results show that the method has a high accuracy in depth positioning, with experimental errors controlled within 10%. This study proves that accurate positioning of pipeline depth could be achieved by substituting signal delay times into the elliptical equation, thereby validating the method’s feasibility in practical applications. The proposed method effectively addressed the shortcomings of existing pipeline depth positioning technologies, providing important theoretical support and a practical reference for future pipeline positioning research. Full article