Interbedded Layers Research Articles

Advancing subsurface analysis: Integrating computer vision and deep learning for the near real-time interpretation of borehole image logs in the Illinois Basin-Decatur Project

The accurate quantification and mapping of subsurface natural fracture systems using borehole imaging logs are critical for the success of CO2 sequestration in geologic formations, optimization of engineered geothermal systems, and hydrocarbon production enhancement. However, traditional interpretation processes suffer from time-consuming procedures and human bias. To address these challenges and expedite fracture analysis, we investigated the application of integrated computer vision and DL workflows to automate image log analysis. Specifically, the design of our workflow was crafted to swiftly detect fractures and baffles by using actual electrical resistivity of borehole wall from microresistivity imaging device alongside their binary representation. This novel approach significantly reduces computational time while providing invaluable insights. By incorporating conventional logging and microseismic data, we present a regional subsurface natural fracture mapping technique. Through the minimization of human bias in image log analysis, our automated workflow achieves reduced fracture interpretation time and costs while ensuring robust and reproducible results. We demonstrated the efficacy of our approach by applying the workflow to the Illinois Basin-Decatur Project site. The automated workflow successfully identified major fractured zones, multiple baffles, and an interbedded layer with a high resolution of 0.01 ft or 0.12 in. (0.3 cm) and can be upscaled to any desired resolution. Validation through microseismic and image log interpretations allows for accurate and near-real-time mapping of fractures and baffles, significantly enhancing CO2 pressure forecasting and postinjection site care. Our approach stands out due to its robustness, consistency, and reduced computational cost compared with alternative feature extraction technologies. It presents exciting possibilities for advancing CO2 sequestration and engineered geothermal efforts by offering comprehensive and efficient fracture mapping solutions. This technology can contribute significantly to the optimization of CO2 sequestration projects, facilitating sustainable environmental practices, and combating climate change.

A cone penetration test database for multiple thin-layer correction procedure development

Cone penetration tests (CPTs) are a commonly used in situ method to characterize soil. The recorded data are used for various applications, including earthquake-induced liquefaction evaluation. However, data recorded at a given depth in a CPT sounding are influenced by the properties of all the soil that falls within the zone of influence around the cone tip rather than only the soil at that particular depth. This causes data to be blurred or averaged in layered zones, a phenomenon referred to as multiple thin-layer effects. Multiple thin-layer effects can result in the inaccurate characterization of the thickness and stiffness of thin, interbedded layers. Correction procedures have been proposed to adjust CPT tip resistance for multiple thin-layer effects, but many procedures become less effective as layer thickness decreases. To compare or improve these procedures and to develop new ones, it is critical to have pairs of measured tip resistance ( q m) and true tip resistance ( q t) data, where q m is the tip resistance recorded by the CPT in a layered profile, and q t represents the tip resistance that would be measured in the profile absent of multiple thin-layer effects. Unfortunately, data sets containing q m and q t pairs are extremely rare. Accordingly, this article presents a unique database containing laboratory and numerically generated CPT data from 49 highly interlayered soil profiles. Both q m and q t are provided for each profile. An accompanying Jupyter notebook is provided to facilitate the use of the data and prepare them for future statistical learning (or other) applications to support multiple thin-layer correction procedure development.

A Prediction Model of Coal Seam Roof Water Abundance Based on PSO-GA-BP Neural Network

With the gradual increase of coal production capacity, the issue of water hazards in coal seam roofs is increasing in prominence. Accurate and effective prediction of the water content of the roof aquifer, based on limited hydrogeological data, is critical to the identification of the central area of prevention and control of coal seam roof water damage and the reduction of the incidence of such accidents in coal mines. In this paper, we establish a prediction model for the water abundance of the roof slab aquifer, using a PSO-GA-BP neural network. Our model is based on five key factors: aquifer thickness, permeability coefficient, core recovery, number of sandstone and mudstone interbedded layers, and fold fluctuation. The model integrates the genetic algorithm (GA) into the particle swarm optimization (PSO) algorithm, with the particle swarm optimization algorithm serving as the primary approach. It utilizes adaptive inertia weight and quadratic optimization of the weights and thresholds of the backpropagation neural network to minimize the output error threshold for the purpose of minimizing output errors. The prediction model is applied to hydrogeology and coal mine production for the first time. The model is trained using 100 data samples collected by the Surfer 13 software. These samples help to accurately predict the unit inflow of water. The model is then compared with traditional forecasting methods such as FAHP, BP, and GA-BP neural network models to determine its efficiency. The study found that the PSO-GA-BP neural network model accurately predicts aquifer water abundance with higher precision. The root mean square error (RMSE) of the test set is determined to be 8.7 × 10−4, and the fitting result is measured at 0.9999, indicating minimal error with actual values of the sample. According to the prediction results of the test set, the water abundance capacity of the No. 7 coal mine in Hami Danan Lake is divided, and it is found that the overall difference between the results and the actual value is small, which verifies the reliability of the model. According to the results of the water abundance division, strong water abundance areas are mainly concentrated in the third-partition area. This study provides a new method for the prediction of aquifer water abundance, improves the prediction accuracy of aquifer water abundance, reduces the cost of coal mine production, and provides a scientific evaluation method and a theoretical basis for the prevention and control of water disasters in coal seam roofs.

Internal structure of an active landslide based on ERT and DP data: New insights from the Hofermühle landslide observatory in Lower Austria

Slopes with clay-rich, deeply weathered soils, such as those present in the Flysch Zone of Lower Austria, are prone to landslide processes. Even though generally being of low magnitude and velocity, they can cause substantial economic losses and threaten settlements as well as infrastructure. Previous studies have demonstrated the importance of sub-surface information to further increase our understanding on landslide processes and triggers in different areas as well as to support any decision makers to determine any appropriate landslide mitigation measures. The combination of direct and indirect methods thereby has proven to be an adequate methodology, yet case studies are still needed to develop a universal strategy for the investigation of clay-rich landslides. In this study, we applied Electrical Resistivity Tomography (ERT) and Dynamic Probing Medium (DPM) to further investigate the complex Hofermühle landslide in the Flysch Zone of Lower Austria in order to improve our knowledge on sub-surface conditions. The focus is on the initially activated main landslide area, which has already formed earth-flow-like processes in the past. The methodology facilitated a representative characterization of the sub-surface. We were able to approximate the geometry and depth of slip surfaces, as well as the transition to bedrock, allowing us to delimit those parts of the slope which are likely to fail and, respectively be re-activated in the future. The results show that a range of thicknesses can be found in the investigated part of the Hofermühle landslide. In particular, near the surface, which has been altered by creep displacement and also by anthropogenic alteration, the resistivity is more variable compared to deeper, presumably less disturbed, layers. Furthermore, it is assumed that clay particles are transported with the surface runoff and deposited in the surroundings of the drainage channels, resulting in lower resistivity values and higher saturation at this locations. The location of the slip surface is interpreted to be on the surface of the bedrock, where there is a highly disturbed, clay-rich mass with no interbedded layers. Layers with lower resistivity directly above the bedrock indicate weathered material and remolding of materials during creep.

Evaluation of petrophysical classification of strongly heterogeneous reservoirs based on the MRGC algorithm

The target formation in the study area of the Pearl River Mouth Basin is characterized by complex lithology and thin interbedded layers, with a large pore-permeability distribution range and strongly heterogeneous characteristics, which makes the reservoir pore structure and production capacity significantly different and brings research difficulties for reservoir logging evaluation and desert identification. The conventional reservoir classification method is mainly based on physical research, which requires developing extremely accurate formulas for calculating porosity and permeability; the calculation accuracy of pore permeability of low-porosity and low-permeability reservoirs is difficult to guarantee; and the conventional logging data cannot be comprehensively applied in reservoir classification. In this paper, taking Zhujiang and Zhuhai Formation reservoirs in the Huizhou M oilfield as an example, we integrated core analysis data such as core cast thin section, pore permeability data, rock electrical parameters, grain size, and relative permeability curves and combined with petrophysical parameters and pore structure characteristics to classify the reservoirs. The artificial neural network is used to predict the resistivity of saturated pure water (R0) to remove the influence of oil and gas on reservoir resistivity. The natural gamma ray (GR) “fluctuation” is used to calculate the variance root of variation (GS) to reflect the lithological variability and sedimentary heterogeneity of the reservoir, and then the conventional logging preferences, R0 and Gs (based on GR), are classified based on the automatic clustering MRGC algorithm to classify the logging facies. To classify the petrophysical phase reservoirs under the constraint of pore structure classification, we proposed a petrophysical classification logging model based on the natural gamma curve “fluctuation” intensity for strongly heterogeneous reservoirs. The learning model is extended to the whole area for training and prediction of desert identification, and the prediction results of the model are in good agreement with the actual results, which is important for determining favorable reservoirs in the area and the adjustment of oilfield development measures.

Geological understanding of permeability upscaling in mixed carbonate siliciclastic reservoirs: An outcrop approach, Miocene Dam formation, eastern Saudi Arabia

In reservoir modeling and simulation, upscaling a fine-grid model (scale of millions of cells), which includes numerous geological details to a coarser grid model (scale of thousands of cells), is indispensable to reduce unachievably high computational time and costs. The upscaling process usually results in losing essential details of the fine-scale model and may introduce overestimating or underestimating reservoir properties. Although numerous mathematical approaches have been developed to reduce such limitations, linking upscaling process to the conceptual understanding of sedimentary geology is less well addressed. Such linkage is critical to establishing a predictive conceptual model of factors that affect the upscaling process, such as heterogeneity and connectivity of reservoir rocks. This study generated several upscaling scenarios and performed multiple runs of fluid flow simulation for three-dimensional porosity and permeability models of carbonate strata deposited in a tidal flat setting (the Miocene Dam Formation, eastern Saudi Arabia). The objective was to understand porosity and permeability upscaling in tidal flat carbonate reservoirs based on lithological distribution and mainly answer questions related to the impact of increasing cell size on the distribution of petrophysical properties and the effect of averaging methods (harmonic, geometric, and arithmetic) on permeability upscaling of tidal flat carbonate. The results showed that porosity values in the tidal flat carbonate are sensitive to upscaling procedures. The mean of the porosity values increases substantially with increasing the cell size of the upscaled models and results in an overestimation of the volumetric parameters of the fine-grid model. A possible reason for such overestimation is the diminishing of the percentage of the cells representing the mud-dominated facies, which in the field occur as thin and interbedded layers. Upscaled permeability showed variation based on averaging methods, and the results from fluid flow simulation provide means to select the appropriate upscaled permeability based on lithofacies distribution. Collectively, these results suggested that a geological understanding of the lithofacies distribution is necessary for the upscaling process. Such knowledge helps to select the appropriate cell size and method for permeability averaging.

ОБРАБОТКА АНОМАЛИЙ СИЛЫ ТЯЖЕСТИ НА ОСНОВЕ АППРОКСИМАЦИЙ ПОЛЯ МЕТОДОМ НАИМЕНЬШИХ КВАДРАТОВ (НА ПРИМЕРЕ ВОСТОЧНОГО ЗАБАЙКАЛЬЯ)

An alternative technique for gravimetric data processing using approximations of the gravity anomaly field by the reduction surface is described. The approach peculiarity is the representation of reductions in the form of regional trend, where the correction for an interbedded layer is excluded without a certain density value. The field approximation algorithm is based on the least squares method. The results of research, conclusions and recommendations for the gravity anomalies at other geological exploration targets are presented.

Study on effects of highly deviated well on thin interbedded reservoirs fracturing

Highly deviated well is widely applied in thin interbedded reservoirs fracturing in changqing oilfield. the oil production data shows that highly deviated fracturing well can increase the oil production compared with horizontal well fracturing, which suggests that highly deviated well fracturing is more efficient. However, it still needs deeper understanding for the mechanism of highly deviated well increase oil production, to study this problem, True-axial hydraulic fracturing physical simulation test is carried out on two kinds of cement specimen with interlayers, the results show that cement specimen for highly deviated well is more productive because fractures are more likely to cross the interbedded layers and connect oil reservoirs that separated by interlayers. Further research on the mechanism of highly deviated well fracture crossing interbedded layers is conducted via numerical simulation. Cohesive zone model is adopted to simulate the propagation of fracture in highly deviated well and horizontal well to compare the difference of thin interbedded layers stress. the results show that due to the deflection of highly deviated well fracture during propagation, the reservoir mass is divided into two parts, which causes relative displacement of rock mass on both sides of the fracture under the effect of vertical principal stress, thin interlayer eventually got broken under the action of tensile and shear stress. Both laboratory tests and numerical simulation results show that highly deviated wells have stronger interlayer penetration capability, which can improve the fracturing effect of thin interbedded reservoirs.

Study on the Mechanical Properties and Failure Law of Rocks with Interbedded Sand and Mud.

In view of the borehole instability during the drilling process of the thin sand and mud interbedded sections in the Shahejie Formation, the physicochemical and mechanical properties of sand and mud interbed rock were studied through a series of laboratory tests to determine the main factors influencing the formation instability. The effects of fracture development of interbed sand and mud, mechanical weak plane, borehole trajectory, and seepage effect on borehole stability were evaluated and analyzed through the established model. The results indicated that the microcracks are developed on the lithologic interface due to the change of lithology of the sand-mud interbed. The anisotropy of the mechanical properties of the rocks with interbedded sand and mud is obvious, which leads to the great mechanical weak plane effect on the wellbore stability. The bottom-hole pressure difference leads to the seepage effect, which reduces the effective supporting force of the drilling fluid on the borehole wall and promotes rock sliding and failure along the lithologic interface developed by the sand-mud thin interbedded layer. Considering the influence of the borehole trajectory, mechanical weak plane, and seepage effect, the recommended drilling fluid density in the deviated section is 1.69 g/cm3. The wellbore stability is the best when drilling along the direction of the minimum horizontal principal stress in the horizontal section. Further strengthening the plugging performance of the drilling fluid, drilling through the microfractures vertically on the interbedded lithologic interface, and reducing the lateral vibration of the drilling tools as far as possible are necessary. The research results provide a theoretical basis for the safe drilling of thin sand and mud interbedded strata.

Evidence of large water-level variations found in deltaic sediments of a tropical deep lake in the karst mountains of the Lacandon forest, Mexico

Lake Tzibaná is one of the largest (1.27 km2) and deepest (Zmax = 52 m) karstic lakes in the UNESCO’s Biosphere Reserve “Nahá-Metzabok” and in the Lacandon Forest, southeastern Mexico. It archives sediments from multiple sources and the inflowing Nahá River forms deltaic deposits. In 2019, the water level in Lake Tzibaná declined by ~ 15 m, persisting for 4 months and exposing the Nahá River Delta. A geophysical profile on the exposed delta revealed an accumulation of ~ 20 m of such deposits. Three sediment outcrops from an inactive channel in the Nahá River Delta, which ranged in height from 0.6 to 1.43 m, were sampled and a multi-proxy analysis of biological remains and geochemical variables was conducted. Four facies were observed: (1) massive-coarse sand, (2) fine sand, (3) dark leaf litter and (4) massive silty clay, each characterized by specific microcrustacean, testate amoebae and diatom taxa. Six dark leaf litter horizons were radiocarbon dated and revealed a complex depositional history including inverted ages making the establishment of an age model difficult. Nevertheless, past lake-level changes and the formation of the four facies match three characteristic water-level stages, which can also be observed on recent satellite images: (1) Massive-coarse sand deposits, with compositional and sedimentological characteristics of a shoreline environment and fluvial lateral banks, were formed during large-magnitude reductions in the lake level, similar to the one in 2019, (2) Interbedded layers of fine sand and dark leaf litter, currently found in low-energy fluvial environments, were formed during shorter and less pronounced decrease intervals, and (3) Massive silty clay, with distinctive microorganisms from low-energy lacustrine environments, is deposited during high water-level stages, when the delta is covered by water. Our findings illustrate how hydrological changes alter sedimentary dynamics in deltaic areas of lakes. Despite the complexity of their depositional processes, deltaic records can serve as a complementary source of paleolimnological information to records from distal zones due to their sensitivity to variations in water level, especially during extreme and prolonged desiccation events. Future research should attempt to combine evidences from deltaic and sediment sequences from deeper zones of Lake Tzibaná to reconstruct water-level variations during the entire Holocene. Understanding past lake-level reductions is not only relevant for the local indigenous communities but also crucial for the conservation of this ecosystem of international importance.

Multiparameter model building for the Qiuyue structure using 4C ocean-bottom seismometer data

Thin sand-mud-coal interbedded layers and multiples caused by shallow water pose great challenges to conventional 3D multichannel seismic techniques used to detect the deeply buried reservoirs in the Qiuyue field. In 2017, a dense ocean-bottom-seismometer (OBS) acquisition program acquired a 4C data set in the East China Sea. To delineate the deep reservoir structures in the Qiuyue field, we have applied a full-waveform inversion (FWI) workflow to this dense 4C OBS data set. After preprocessing, including receiver geometry correction, moveout correction, component rotation, and energy transformation from three dimensions to two dimensions, preconditioned first-arrival traveltime tomography based on an improved scattering-integral algorithm is applied to construct an initial P-wave velocity model. To eliminate the influence of the wavelet estimation process, a convolutional-wavefield-based objective function for the preprocessed hydrophone component is used during acoustic FWI. By inverting the waveforms associated with early arrivals, a relatively high-resolution underground P-wave velocity model is obtained, with updates at a depth of 2.0 and 4.7 km. The initial S-wave velocity and density models are then constructed based on their prior relationships to the P-wave velocity, accompanied by a reciprocal source-independent elastic FWI to refine both velocity models. Compared with a traditional workflow, guided by stacking velocity analysis or migration velocity analysis, and using only the pressure component or other single component, the workflow presented in this study represents a good approach for inverting the 4C OBS data set to characterize subseafloor velocity structures.

Astrochronology of the Ediacaran Shuram carbon isotope excursion, Oman

The Ediacaran is a highly dynamic period in terms of large perturbations in Earth's atmosphere, biosphere, and climate. Among these perturbations, a pronounced negative carbon isotope excursion, known as the Shuram excursion (SE), is characterized by the most depleted δ13C values (-12‰) that have ever been observed in the geological record. A poorly determined chronostratigraphic framework makes the SE difficult to correlate and compare globally. Therefore, it is hard to study the potential connection between the SE and coeval climate and biological variations. Here, we present a high-resolution astrochronological study of the Ediacaran Shuram and Buah Formations, Nafun Group, Oman, in which the SE is reported for the first time. Power spectral analysis of the 600-m long gamma ray log of the Miqrat-1 Well shows that a hierarchy of astronomically-forced climate cycles (eccentricity, obliquity, and precession) is accurately-preserved. Using multiple statistical tests, we constructed a sedimentation rate variation profile that covers the entire SE, which is characterized by low rates in shale-dominated layers and high rates in shale-carbonate interbedded layers. The duration of the SE in Oman is suggested to be 7.7 ± 0.2 Myr, which agrees with estimates from South Australia, South China, and the United States. An identical duration of the SE supports its global synchroneity and indicates a primary origin of the depleted δ13C values. Combined with the newly proposed termination age (562.5 ± 1.1 Ma) of the SE, our astrochronological results suggest that the onset age of the excursion is 570.2 ± 1.1 Ma. The astrochronology of the SE delineates the tempo of the excursion, with a rapid decrease (∼ 1 Myr) from the onset to its isotopic nadir followed by a more gradual recovery (∼ 6–7 Myr) towards the termination. The new chronostratigraphic framework permits further investigations of the potential causal links between the global carbon cycle and the widespread glaciation, the oceanic oxygenation, and the biological diversification in Ediacaran time.

Effect of the Soft and Hard Interbedded Layers of Bedrock on the Mechanical Characteristics of Stabilizing Piles

In this paper, the mechanical characteristics of stabilizing piles embedded in layered bedrocks are studied both experimentally and numerically. The influence of soft and hard interbedded layers in the structure of the bedrock on the mechanical characteristics of stabilizing piles is particularly investigated. The discrete element method is used to numerically investigate the response of the stabilizing piles embedded in composite and inclined bedrocks. The simulation results and comparison with experimental data are presented to demonstrate the effectiveness and accuracy of the discrete element model. As the dip angle of the soft/hard interbedded bedrock layers increases from 0° to 45°, it is observed that the displacement of the embedded section of the stabilizing pile increases and reaches the maximum displacement at 45°. In the range of 45° to 75°, the influence of the dip angle of the layered bedrock on the displacement of the embedded section of the pile is gradually reduced.

Time Series of Landsat Imagery Shows Vegetation Recovery in Two Fragile Karst Watersheds in Southwest China from 1988 to 2016

Since the implementation of China’s afforestation and conservation projects during recent decades, an increasing number of studies have reported greening trends in the karst regions of southwest China using coarse-resolution satellite imagery, but small-scale changes in the heterogenous landscapes remain largely unknown. Focusing on two typical karst regions in the Nandong and Xiaojiang watersheds in Yunnan province, we processed 2,497 Landsat scenes from 1988 to 2016 using the Google Earth Engine cloud platform and analyzed vegetation trends and associated drivers. We found that both watersheds experienced significant increasing trends in annual fractional vegetation cover, at a rate of 0.0027 year−1 and 0.0020 year−1, respectively. Notably, the greening trends have been intensifying during the conservation period (2001–2016) even under unfavorable climate conditions. Human-induced ecological engineering was the primary factor for the increased greenness. Moreover, vegetation change responded differently to variations in topographic gradients and lithological types. Relatively more vegetation recovery was found in regions with moderate slopes and elevation, and pure limestone, limestone and dolomite interbedded layer as well as impure carbonate rocks than non-karst rocks. Partial correlation analysis of vegetation trends and temperature and precipitation trends suggested that climate change played a minor role in vegetation recovery. Our findings contribute to an improved understanding of the mechanisms behind vegetation changes in karst areas and may provide scientific supports for local afforestation and conservation policies.

Dynamic response of pipe pile embedded in layered visco elastic media with radial inhomogeneity under vertical excitation

A new mechanical model for predicting the vibration of a pipe pile embedded in longitudinally layered visco-elastic media with radial inhomogeneity is proposed by extending Novak\'s plain-strain model and complex stiffness method to consider viscous-type damping. The analytical solutions for the dynamic impedance, the velocity admittance and the reflected signal of wave velocity at the pile head are also derived and subsequently verified by comparison with existing solutions. An extensive parametric analysis is further performed to examine the effects of shear modulus, viscous damping coefficient, coefficient of disturbance degree, weakening or strengthening range of surrounding soil and longitudinal soft or hard interbedded layer on the velocity admittance and the reflected signal of wave velocity at the pile head. It is demonstrated that the proposed model and the obtained solutions provide extensive possibilities for practical application compared with previous related studies.

Pre-stack AVA Inversion by Using Propagator Matrix Forward Modeling

Most existing amplitude variation with angle (AVA) inversions are based on the exact Zoeppritz equation or its approximations. These modeling methods, which are ray-tracing-based and describe P-wave primary reflections only, lead to exacting requirements for pre-processing of the input data. Current processing is inadequate to satisfy these demands, especially for removing the effects of transmission losses, P-wave multiples and various converted-wave modes. By using input data with processing errors, inversion results of primary-only methods are predictably not accurate enough. The propagator matrix (PM), like the reflectivity method, uses an analytical solution to the wave equation and considers full-wave propagation effects in horizontal or nearly horizontal multilayered earth models. The numerical examples verify that a PM can effectively estimate transmission losses, multi-reflections and the comprehensive responses of thin interbedded layers, and also has higher reflection sensitivities to P-wave and S-wave velocity and density, as compared with ray-tracing-based AVA modelling. A pre-stack AVA three-parameter inversion by using a PM as the forward engine is proposed. Following a Bayesian approach, the inversion is stabilized by including the correlation of P-wave velocity, S-wave velocity and density. For inversion accuracy, the limited-memory Broyden–Fletcher–Goldfarb–Shanno (L-BFGS) optimization method is used to solve the augmented function, and the generalized cross-validation (GCV) criterion (Huang et al. in J Geophys Eng 14(1):100–112, 2017) is introduced to adaptively acquire the regularization parameter. Theoretical model inversion analysis shows that the proposed inversion can make use of transmission losses, P-wave multiples and converted wave modes, which not only cost-effectively simplifies the pre-processing, but also generates reasonable inverted results for multilayered conditions. The proposed inversion is then applied to a set of real data, and a comparison with Zoeppritz equation-based inversion demonstrates that PM inversion is clearly superior to Zoeppritz equation-based inversion in terms of stability and accuracy.

Estruturas locais condicionantes das características geométricas e hidráulicas do sistema Aquífero Guarani (SAG): alto estrutural da fazenda Santa Helena, município de Boa Esperança do Sul (SP)

Denominou-se Alto Estrutural da Fazenda Santa Helena (AEFSH) à subestrutura identificada em subsuperfície por perfurações de poços para captação de água subterrânea no Sistema Aquífero Guarani (SAG), alojada no Alto do Jacaré-Guaçu na região das bacias hidrográficas dos rios Jacaré-Guaçu e Jacaré-Pepira, Município de Boa Esperança do Sul (SP). Ainda com extensão não delimitada, o AEFSH representa estrutura de pequeno porte que condiciona as características geométricas e hidráulicas do SAG. Dados de poços profundos e de perfilagem geofísica mostraram que o SAG está representado, na área, por arenitos finos a muito finos, argilosos, intercalados por frequentes camadas de argilito. Essa sucessão, pertencente à porção basal da Formação Piramboia, assenta-se sobre siltitos e argilitos da Formação Corumbataí. A espessura reduzida, da ordem de 80 m, e as características litológicas locais do SAG afetam negativamente a transmissividade do aquífero, resultando em poços com baixa produtividade. O presente trabalho dá conhecimento da existência dessa subestrutura que exerce influência no armazenamento hídrico e nas potencialidades locais do SAG, e chama a atenção para a possibilidade de haver inúmeras outras em contexto geológico similar ou ocultas sob a cobertura basáltica da Formação Serra Geral e sedimentar do Grupo Bauru.

The genesis of the Dahebian Zn-Pb deposit and associated barite mineralization: Implications for hydrothermal fluid venting events along the Nanhua Basin, South China

The Dahebian stratiform barite deposit, which is situated in the Nanhua Basin, is one of the world’s largest and most important barite deposits. This deposit was formed through sedimentary exhalative processes in the early Cambrian stage. Recently, beneath stratiform barite ore, stratabound Zn-Pb-(Fe-bearing) sulfide mineralization, which is hosted by the Doushantuo Formation, was discovered. Ores that represent Zn-Pb sulfide mineralization are mainly discordant but stratabound. The Doushantuo Formation consists of laminated interbedded layers of micritic dolomite and carbonaceous mudstone, associated with phosphorite and chert. The sulfide ores consist primarily of sphalerite, pyrite and galena. The associated gangue minerals are barite, quartz, minor calcite, as well as trace amounts of apatite and hyalophane. Hyalophane found in the stratiform barite ore is richer in barium but poorer in potassium than that associated with the sulfide ores. This outcome corresponds to ascending hydrothermal fluids that are richer in barium along with sulfide mineralization. Investigation of the ore fluid reveals relatively high temperature (142–368 °C) with scattered salinity (0.53–25.62 wt% NaCl eq.). This finding suggests that fluid cooling and/or mixing with seawater could be the primary mechanisms that prompted the ore formation. Sulfides selected from the zinc-lead sulfide ores and stratiform barite ore have similar sulfur isotopic compositions, with δ34S values ranging from 13.5‰ to 30.0‰; δ34S values of barite from these ores are analogous, with δ34S values ranging from 29.5‰ to 55.1‰. The sulfur isotopic fractionation between minerals (barite and sulfide) and the early Cambrian seawater is ΔBarite-Seawater = 7.8‰ and ΔSulfide-Seawater = −12.1‰, respectively, demonstrating that the sulfur in the Dahebian zinc-lead deposit and the stratiform barite deposit were derived from the early Cambrian stratified seawater column. Lead isotopic compositions of sulfide ores indicate that these ore metals are mainly sourced from rocks of the Doushantuo Formation and the underlying fold basement.Therefore, the Dahebian zinc-lead deposit and stratiform barite deposit probably arose from Selwyn-Type sedimentary exhalative hydrothermal fluids. Zn-Pb sulfides were mineralized in the feeder zone of these hydrothermal fluids, and the stratiform barite ore deposits represent the upper sedimentary-exhalative mineralization. This finding points to intensive Zn-Pb-Fe-Ba hydrothermal fluid venting into the Nanhua Basin and to relatively oxic deep ocean waters during the early Cambrian.

The genesis and evolution of carbonate minerals in shale oil formations from Dongying depression, Bohai Bay Basin, China

Shale oil is attracting increasing attention in the petroleum industry as an essential target of unconventional oil and gas exploration. Recent exploration efforts have indicated that laminar carbonates are closely related to the favorable depositional strata of shale oil. This research focused on inter-bedded layers of laminar carbonates as well as mudstone and shale in the Dongying depression of the Bohai Bay Basin in eastern China, and attempted to reveal the genesis and evolution of the carbonates by means of drill core observations, thin sections, high resolution scanning electron microscopic observations, and fluorometric, cathodoluminescence and geochemical analyses. The results demonstrated that: (1) the carbonates could be categorized into two groups, crystalline carbonates and micritic carbonates; (2) the crystalline carbonates were well crystallized and greenish under fluorescent light; and (3) the micritic carbonates were not well crystallized and had biotic textures. It was discovered that the crystalline carbonates were mainly developed in the shale layer and were formed from the late-filling effects of the diagenetic cracks along the shale fissility planes; shale layers with crystalline carbonates are usually favorable for shale oil reserves. The micritic carbonates were formed from direct deposition controlled by biological effects in the stratified flows of the seasonal lake basins and are unfavorable for shale oil reserves.

绿洲边缘夹粘沙丘持水特性

PDF HTML阅读 XML下载 导出引用 引用提醒 绿洲边缘夹粘沙丘持水特性 DOI: 10.5846/stxb201705250970 作者: 作者单位: 中国科学院西北生态环境资源研究院 中国生态系统研究网络临泽内陆河流域研究站 中国科学院内陆河流域生态水文重点实验室,中国科学院西北生态环境资源研究院 中国生态系统研究网络临泽内陆河流域研究站 中国科学院内陆河流域生态水文重点实验室,中国科学院西北生态环境资源研究院 中国生态系统研究网络临泽内陆河流域研究站 中国科学院内陆河流域生态水文重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41630861，41501577） Water retention of the clay interlayer of dunes at the edge of an oasis Author: Affiliation: Northwest Institute of Eco-Environment and Resources, CAS,Northwest Institute of Eco-Environment and Resources, CAS, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:夹粘沙丘是指剖面中分布有一层红褐色粘化层的沙丘，其夹粘层埋藏深度常在120-500cm左右，厚度在40-100cm之间，粘粉粒含量达到90%以上。夹粘沙丘人工梭梭固沙植被郁闭度在0.5以上，明显高于相同水热条件下的植被生产力，这可能与夹粘层通过改变土壤持水性及水分状况，从而提高了土壤水分承载力有关。以河西走廊绿洲边缘夹粘沙丘为研究对象，在测定0-8.0m剖面土壤物理性质和土壤水分特征曲线的基础上，计算了土壤孔隙分布和持水特性，研究了剖面中土壤持水性的变化规律及其影响因素。结果表明：（1）夹粘层土壤含水量最高，上覆沙土土壤含水量最少且随深度增加而增加，下伏沙土受地下水毛管作用影响水分含量较高；（2）土壤机械组成决定了不同土层的持水特性，土壤中粘粉粒含量越高，田间持水量和饱和含水量就越大，夹粘层的土壤持水性远高于沙土层；（3）夹粘层是沙丘土壤水分暂时贮存的重要土层，可以为植被提供深层土壤水分，这对绿洲边缘人工固沙植被的生存和繁衍有重要影响，而土壤持水性和毛管作用的强弱决定了夹粘层对沙丘水分调节能力的强弱。本研究为深入理解绿洲边缘雨养固沙植被斑块状分布的机理提供了一定的理论依据。 Abstract:A sandwich dune's profile consists of layers with different soil textures, the upper and lower of which are sandy soil layers, and there is a fine soil pan between the surface and the subsoil. The clay interlayer is composed of silty loam containing over 90% silt and clay. Deposits of this layer occur at depths of 120-500cm and it ranges in thickness from 40 to 100cm. In arid areas with precipitation of less than 200mm, artificial sand-fixing vegetation coverage is approximately 10% to 15%; however, the vegetation coverage of the study area with 117mm mean annual precipitation is approximately 65%, which does not meet the zonal water and heat conditions. Water retention is considered to play an important part in affecting the water conditions and soil water carrying capacity of dunes. With regards to water retention, Betti et al. have analyzed the effects of soil texture on water retention, revealing that when the sand content is increased, water retention becomes weaker, and the soil layer has a significant effect on the water-holding capacity, and their studies have focused on analysis of the water-holding capacity of homogeneous soil. In order to study the characteristics and mechanisms of the response of the clay interlayer to water retention, we measured the soil water characteristic curve based on the centrifuge test, particle size measured by Mastersizer-2000, and pore distribution based on the measured soil water characteristic curve and the calculated equivalent porosity at different depths of a sandwich dune. Our results show the following patterns. (1) The soil moisture content of the clay interlayer was the highest, soil water content increased slightly with depth in the surface soil, and the soil moisture of the subsoil was higher than in the surface, which was affected by the capillary action of groundwater. (2) Field capacity, wilting coefficient, saturated water content, total porosity, and aeration porosity were significantly correlated with soil physical properties, such as bulk density, sand content, clay content, and particle size. Sandy soil layers were at 0-4.0m and 4.6-8.0m. The soil water characteristic curves of these profiles were steep and the soil was loose (aeration porosity, 14%-27%) with poor soil water retention. The layer at 4.0-4.6m was an interbedded layer of silty loam, the soil water characteristic curves of which was smooth and the soil water content was high when the soil water suction was high.This type of soil had less aeration porosity, leading to higher soil water-holding capacity than the upper and lower sandy layers. Furthermore, correlation analysis showed that capillary porosity was not significantly correlated with soil physical properties, but was weakly related to soil water content, and increased significantly only at both the interface between the sandy layer and silty loam layer, and the water table. To a certain extent, the distribution of soil porosity affected the soil moisture content and water conveyance between the clay interlayer and the sand layer. In conclusion, soil textures lead to considerable differences in soil water retention of dunes at the edge of an oasis. The clay interlayer can hold more water compared with all profiles, which improves the water conditions of the dune. (3) The soil pan is the region where water collects, and provides water resources for plants. It plays an important role in the improvement of sand-fixing vegetation of dunes at the edge of an oasis. Further, the ability of the clay interlayer to regulate the water conditions of dunes depends on soil water retention and soil capillarity. In conclusion, our findings should provide strong support for future understanding of the mechanism of spatial patterns of artificial sand-fixing vegetation. 参考文献 相似文献 引证文献