Clay Organic Matter Research Articles

Shale Reservoir Rock Physics Modeling and “Sweet Spot” Prediction Based on Digital Core

Abstract With the increasing advancement in shale exploration and development, the complex pore structure and organic-rich characteristics of shale have gradually become the focus of rock physics models. This study combined digital core technology to obtain detailed information on the shale mineral composition, content, pore and crack contents, and composition. The isotropic self-compatible approximation (SCA) model was used to couple the shale minerals and hard pores to construct a brittle mineral framework. The VRH model was used to mix kerogen and clay, and the SCA-DEM (differential equivalent medium) model was used to add organic pores to construct a clay-organic matter mineral framework. The anisotropic SCA model treated the clay-organic matter mineral framework as an inclusion added to the brittle mineral framework to construct the shale mineral framework. The Eshelby–Cheng model was used to add fracture to the mineral framework and establish a physical shale model. This model was used to optimise the selection of sensitive elastic parameters for physical properties such as brittle mineral and kerogen content, fracture density, and porosity, and the optimisation results were combined to construct an explanatory quantity template. In addition, according to actual data from a study area in southwestern China, we combined to the interpretation chart established by the model to perform isotropic inversion. Then, we analyzed and interpreted the brittleness index (BI) and total organic carbon (TOC) content of the reservoir and predicted the sweet spot area of the shale reservoir.

Sedimentary dynamics and depositional model for mud accumulation in deep lake basins: A case study in the Upper Triassic Chang-7 Member, Ordos Basin, northern China

Shales in deep lake basins have become the main focus of continental shale oil and gas exploration. In order to highlight the sedimentary dynamics of mud deposition in deep lake basins, a combination of core observation, thin section examination, X-ray diffraction, and QEMSCAN (quantitative evaluation of minerals by scanning electron microscopy) was used to analyze the depositional characteristics of mudrocks in the Chang-7 Member from the Yanchang Formation (Upper Triassic) in Ordos Basin, and to establish a depositional model for mud accumulation in deep lake basins. This study recognizes four mudrock lithofacies in the Chang-7 Member: (1) the laminated silt-bearing mudstone, which generally develops a binary composition of “silt–clay” or a ternary composition of “silt–clay–organic matter”; (2) the graded mudstone, mainly composed of dark gray and gray-black mudstone sandwiched by silt-bearing mudstone; (3) the massive mudstone, internally showing a uniform distribution of quartz, clay, and carbonate minerals, with also a small amount of organic detritus; and (4) the laminated shale, which is generally composed of clay laminae, and organic laminae of the former two. Sediment supply, topographic slope, and flood intensity combine to control the evolution of gravity flows and the transport and deposition of the mudrock in the Chang-7 Member. The influence of orogeny provides terrain gradient, water depth, abundant sediments at source areas, and triggering mechanism for the formation of gravity flows. Floods triggered by wetting events provide the impetus for sediment transport. Mud deposition in the Chang-7 Member was mainly related to the transport and sedimentation of mud by hyperpycnal flows and rapid sedimentation by buoyant plume flocculation. A comprehensive evolutionary model for shale accumulation in the deep lake basin is established by integrating various triggering mechanisms and mud transport sedimentary processes.

The fate of carbon dioxide generated by decomposition of the organic matter in the Boom Clay upon heating at 80 °C: The buffering role of carbonates and implications for the geological disposal of heat-emitting waste

Short-term and long-term hydrothermal experiments were performed with the bulk Boom Clay (Rupelian, Belgium) involving all its constituents (organic matter, minerals and water) in order to follow CO2 generation primarily formed by organic matter decomposition at 80 °C, the temperature to be reached in the near-field of a repository hosting heat-emitting radioactive waste. The carbon speciation and isotopic data in the sampled gas, liquid and solid phase served as a base for mass balance calculations and evaluation of the fate of the carbon dioxide in the studied system. The maximum CO2 yields are lower (1.9 mmol CO2/kg clay after 21 days) in the short-term hydrothermal tests as compared to the long-term tests (maximum 13.3 mmol CO2/kg clay after 7 years) thus underestimating the total capacity of the clay to generate CO2. This is supported by still continuous generation of the carboxylic acids, important precursors of the released CO2 gas, after 21 days. The stable isotope data (δ13C and δ18O) confirm that CO2 gas released from the Boom Clay is of organic origin. The early released CO2 gas is isotopically lighter (−22.2 to −23.3‰) than the reference δ13C of the CO2 (g) and isotopically heavier than the parent kerogen (−25.5 ‰) in the undisturbed Boom Clay. The early CO2 gas is likely out of isotope equilibrium with either dissolved inorganic carbon or solid carbonates. However, measured and extrapolated δ13C values of CO2 gas indicate the tendency towards isotope equilibrium between CO2 gas and both dissolved and solid inorganic carbon on the longer runs (up to 7 years). The precipitation of the carbonates and recycling of the organic matter derived CO2 in the carbonates is further supported by elemental chemistry and mass balance calculations. Altogether, our results suggest that the CO2 (g) released by Boom Clay organic matter is buffered by the carbonates (both dissolved and solid) present in Boom Clay. Thus, no net accumulation of CO2 (g) from organic matter is expected.

Reservoir characteristics and controlling factors of the middle–high maturity multiple lithofacies reservoirs of the Lianggaoshan Formation shale strata in the northeastern Sichuan basin, China

The Lianggaoshan Formation, which is located in the northeastern part of the Sichuan Basin, is an important shale oil producer. However, due to the effects of complex petrography, a wide range of maturity, and lower organic matter (OM) content in comparison to other areas, the pore characteristics of different lithofacies are unclear, which severely limits exploration and development. Therefore, by using geochemical, petrological and pore structure characterization experiments, this study thoroughly examines the pore properties of several lithofacies in the Lianggaoshan Formation in Northeast Sichuan. The deposits in the study area are OM-rich laminated argillaceous shale (ORLAS), silty mudstone (SM), OM-low laminated siliceous shale (OLLSS), organic-laminated argillaceous shale (OLLAS), OM-low bedded shale (OLBMS), and (fine) siltstone (FS). With higher porosity and macropore + microfracture volume ratio, ORLAS and OLLSS have better reservoir qualities than the other lithologies, while the reservoir properties of SM and FS are the worst. Hydrocarbon generation and diagenesis affecting pore development include thermal maturation of OM, mechanical compaction, dissolution, and cementation. The porosity and medium–large scale pore volume ratio show a tendency to increase and then decrease with maturity, reaching their highest values at an Eq range of (Ro) = ∼1.6%. Dissolution greatly contributes to pore development. The pore space is primarily sealed by cementation and compaction, which is most evident in SM and FS. In addition to thermal maturity, factors affecting the reservoir properties include clay minerals, siliceous minerals, and total organic carbon (TOC). Clay minerals and OM often form OM–clay mineral complexes, which can promote hydrocarbon generation and pore enlargement through interaction. The properties of the reservoir significantly improved when TOC and clay contents increased. However, the lithology of the study area, which contains a significant concentration of siliceous minerals, is unfavorable to reservoir properties.

Depositional and diagenetic controls on hydrocarbon generation of mudstones through clay–organic matter interactions: A comparative study of the Dongpu Depression, Bohai Bay Basin, China

Although the hydrocarbon generation of mudstones is greatly affected by depositional and diagenetic environments, how they affect the integrated theoretical framework of organic matter (OM) preservation, mudstone formation, and OM diagenetic conversion remains unresolved. Therefore, we addressed this issue from the perspective of clay–OM interactions during mudstone formation and diagenetic evolution. The northern and southern Dongpu Depressions represent two endmembers of depositional (weak vs. strong hydrodynamics and abundant vs. limited terrigenous input) and diagenetic (saline vs. freshwater pore fluid) environments. Results highlighted that the protection of clay minerals on OM preservation was more affected by the depositional fabric than mineral content. For the northern Depression mudstones, the predominance of laminated mudstones and remarkable enrichment of high-hydrogen index OM in the clay-sized fractions indicated the intimate clay-OM associations during mudstone formation, which led to better OM preservation and a higher hydrocarbon generation potential. For the southern Depression mudstones, the scattered distribution of OM particles and inconspicuous OM enrichment in the clay-sized fractions coincided with lower hydrocarbon generation potential. Additionally, the faster smectite illitization accelerated by the saline environment of the northern Depression led to OM desorption. Thus, OM lost the protection of clay minerals and the mineral reactive sites were liberated, both of which were beneficial to hydrocarbon generation. Generally, deposition controlled the material premise and diagenesis determined the hydrocarbon generation impetus. These findings provide a theoretical reference for shale oil accumulation in saline lacustrine systems and can potentially serve as a guide for future oil–gas exploration and development.

Interlayer organic matter within hydroxy-interlayered clay minerals enhances soil organic carbon stability under long-term organic fertilization

The intercalation of organic matter in clay minerals is believed to be essential for soil carbon sequestration because nanoscale interlayer spaces can effectively protect organic matter from degradation. However, the lack of a direct method for the detection of interlayer organic matter has limited the identification of organic matter and the evaluation of the properties of organic matter–clay complexes. In this study, the association between the organic matter and hydroxy-interlayered clay minerals (HIMs) in red earth collected from Qiyang County (Hunan Province) in southeast China was investigated by combining X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM)-electron energy loss spectroscopy (EELS) methods. The presence of organic matter in the interlayer space of HIMs was confirmed by HRTEM-EELS for the first time, providing direct visible evidence of interlayer organic matter in the HIMs of red earth. Hydroxy-Al was identified as the interlayer hydroxy cation in the HIMs. The organic molecules were associated with Al-OH in the interlayered hydroxy-Al polymer and exhibited resistance to oxidation by H2O2. Organic fertilization increased the amount of organic matter on the external surface and in the interlayer space of the HIMs, implying the feasibility of enhanced carbon sequestration in red earth.

Passive of CRFS Technology in Soil-Cement Application

In Brazil, with the ban on the production, sale, and use of chrysotile asbestos, the sector’s industry opted to replace asbestos with CRFS Technology—Cement Reinforced with Synthetic Wire (fiber cement); that is, another product to be disposed of in landfills. This work aimed to determine a composite based on clay, fiber cement powder, and cement that meets the technical specifications of Brazilian soil–cement application standards to contribute to a more sustainable treatment of the future disposal of fiber cement products. With the characterization analysis of the materials, we identified that the clay granulometry is heterogeneous and distributed from 0.1 µm to 25 µm. In comparison, 75% of the fiber cement powder has grains greater than 10 µm. For clay, the liquidity limit is 39.67%, the plasticity limit is 25.01%, and the plasticity index is 14.66%. In the semiquantitative chemical analysis, silicon oxide (SiO2) and calcium oxide (CaO) stood out as the main oxides found, reflected in the mineralogy as quartz and calcium silicate. Therefore, we identified the percentage of organic matter in clay at 2%, using the result of the thermogravimetric analysis. The results described met the normative parameters foreseen for soil–cement applications. That said, the technological characterization was carried out by tests of linear retraction, water absorption, and simple mechanical compression on the specimens made under an axial pressure of 31.2 Mpa in the formulations defined in this work. The formulations with 10% cement and 20% and 30% fiber cement powder are suitable for use in soil–cement bricks, as they have volumetric shrinkage percentages from 2% to 2.5%, water absorption ranging from 18.66% to 19.39%, and simple compressions from 4.25 Mpa to 6.88 Mpa, meeting the requirements of Brazilian standards for soil–cement applications. It is concluded that the results showed that it is possible to produce soil–cement bricks with passive fiber cement products converted into powder, avoiding improper disposal and unwanted environmental impacts.

Study on Organic Matter Enrichment and Reservoir Characteristics of Permian Longtan Formation Shale in Southeast Sichuan

The study of reservoir space development characteristics and the geochemical parameters of the Permian Longtan Formation in the southeast of the Sichuan Basin at Well X1 was analyzed by using core observations, optical thin-section observations, Ar-ion polishing, scanning electron microscopy, and nitrogen adsorption tests. Major and trace elements of samples, the V/Cr, U/T, enrichment coefficients EF (Mo) and EF (U), chemical alteration indexes CIA and Sr/Cu, and Mo, P, and other index values of different samples were calculated based on the test of organic geochemical parameters. The depositional environment of the Longtan Formation in the study area was systematically analyzed. The Longtan Formation was in a warm and humid climate during the deposition period. The main body of the sedimentary water was in an oxygen-depleted state, and a portion of it was in an oxidized state with high biological productivity. Therefore, it had a small deposition rate. The clay mineral content and organic matter content in the sample played a major role in controlling the development of reservoir space. The content of clay minerals in the sample was high, and it was mainly chlorite and a mixed layer of illite/smectite. Under a microscope, it was observed that the mixed layer of flake illite/smectite and chlorite aggregate mostly developed interlayer pores or microfractures, which played a positive role in the specific surface area and pore volume of the sample.

Discussion of “Quantitative evaluation of thixotropy-governed microfabric evolution in soft clays”

The diagenesis of clay minerals and thermal evolution of organic matter (OM) are consistent in space and time in most petroliferous basins. Within these processes, the synchronism of smectite illitization with peak hydrocarbon generation is one of the most important phenomena and the illitization process is believed to play an important role in catalytic effects on the conversion of OM to oil and gas. The variation in the layer charge of montmorillonite (Mt) is a key indicator of illitization. However, the effects of layer charge on OM pyrolysis have not been investigated. In this study, a series of homologous reduced-charge Mt (LiMt) samples were prepared by changing the temperature of heat treatment based on the Hofmann–Klemen effect. The 12-aminolauric acid and Mt were mechanically mixed to prepare clay–OM complexes. Pyrolysis experiments were conducted in a confined gold capsule system, and the gas components were evaluated by gas chromatography. The experimental results show charge reducing changed the solid acidity of Mt and further influence the catalytic activity of Mt on the OM pyrolysis. The solid acidity of Mt first increased and then decreased as the layer charge decreased, while the water content decreased. These sites, especially Brønsted (B) acid sites, catalyzed OM pyrolysis via the carbocation mechanism. The content of iso‐alkanes was controlled by the content of water in Mt because excess water molecules hindered the isomerization reactions occurring at the B acid sites. The CO2 content was affected by both the amount of Lewis (L) acid sites and the water content. These fundamental results suggest that changes of the layer charge in Mt which occurs during the processes of smectite illitization may play an important role in hydrocarbon generation. These findings are important for understanding the organic-inorganic interactions between clays and OM during sedimentation and diagenesis.

Effects of montmorillonite charge reduction on the high-temperature/high-pressure pyrolysis of organic matter

The diagenesis of clay minerals and thermal evolution of organic matter (OM) are consistent in space and time in most petroliferous basins. Within these processes, the synchronism of smectite illitization with peak hydrocarbon generation is one of the most important phenomena and the illitization process is believed to play an important role in catalytic effects on the conversion of OM to oil and gas. The variation in the layer charge of montmorillonite (Mt) is a key indicator of illitization. However, the effects of layer charge on OM pyrolysis have not been investigated. In this study, a series of homologous reduced-charge Mt (LiMt) samples were prepared by changing the temperature of heat treatment based on the Hofmann–Klemen effect. The 12-aminolauric acid and Mt were mechanically mixed to prepare clay–OM complexes. Pyrolysis experiments were conducted in a confined gold capsule system, and the gas components were evaluated by gas chromatography. The experimental results show charge reducing changed the solid acidity of Mt and further influence the catalytic activity of Mt on the OM pyrolysis. The solid acidity of Mt first increased and then decreased as the layer charge decreased, while the water content decreased. These sites, especially Brønsted (B) acid sites, catalyzed OM pyrolysis via the carbocation mechanism. The content of iso‐alkanes was controlled by the content of water in Mt because excess water molecules hindered the isomerization reactions occurring at the B acid sites. The CO2 content was affected by both the amount of Lewis (L) acid sites and the water content. These fundamental results suggest that changes of the layer charge in Mt which occurs during the processes of smectite illitization may play an important role in hydrocarbon generation. These findings are important for understanding the organic-inorganic interactions between clays and OM during sedimentation and diagenesis.

Pore structure and sorption capacity investigations of Ediacaran and Lower Silurian gas shales from the Upper Yangtze platform, China

The shale gas potential of Ediacaran and Lower Silurian shales from the Upper Yangtze platform is assessed in this study with a focus on the contributions of clay minerals and organic matter to sorption capacity. For this purpose, a multidisciplinary assessment was carried out using petrophysical, mineralogical, petrographic and geochemical methods. In terms of TOC contents (4.2%), brittle mineral contents (68.6%) and maximum gas storage capacities (0.054–0.251 mmol/g) Ediacaran shales from this study show comparable properties to other producing shale gas systems although the thermal maturity is extremely high (VRr = 3.6%). When compared to lower Silurian shales from the same region, it is evident that (1) deeper maximum burial and (2) a lack of silica-associated preservation of the pores resulted in a relatively lower mesopore volume, higher micropore volume fraction and lower overall porosity (Ediacaran shales: 1.4–4.6%; Silurian shales: 6.2–7.4%). Gas production is therefore retarded by poor interconnectivity of the pore system, which was qualitatively demonstrated by comparing experimental gas uptake kinetics. TOC content exhibits a prominent control on sorption capacity and micropore volume for both shales. However, different contributions of clay minerals to sorption capacity were identified. This can partly be attributed to different clay types but is likely also related to burial-induced recrystallisation and different origins of illite. Additionally, it was shown that variations in sorption capacity due to incorrect estimates of clay mineral contribution are in the same range as variations due to differences in thermal maturity.Article highlightsPore structure and gas storage characteristics are evaluated for the first time for Ediacaran Shales from the Upper Yangtze platformDue to a lower free gas storage capacity and diffusivity, the Ediacaran shale can be regarded as a less favorable shale gas prospect when compared to the Silurian shaleClay mineral contribution to sorption capacity is evaluated taking clay mineralogy into considerationMaturity-related changes of organic matter sorption capacity have been discussed on the basis of a compiled data set

Micropore Characteristics and Geological Significance of Shale Reservoirs: Case Study of Fuling Shale Gas in Sichuan Basin, China

Several techniques (such as scanning electron microscopy (SEM) and gas adsorption systems) have been used to study the pore features and structures of shale reservoirs. The available methods and techniques have restricted the specific research on micropores, and the morphology, genesis, volume, and main factors controlling pore characteristics are yet to be analyzed. Currently, there is no systematic understanding of the role that these spaces play in gas storage and flow. As such, our understanding of the spatial connectivity of pores and reserves of shale reservoirs is limited. In this study, the pores of the Fuling shale gas reservoir in the Sichuan Basin were systematically observed by SEM and transmission electron microscopy. Images of pores smaller than 2 nm were captured for the first time, and their morphology and genesis were analyzed by combining these images with the rock mineralogy theory. The pore size distribution characteristics of the reservoir were analyzed by the adsorption-mercury injection method and nuclear magnetic resonance, and the main factors controlling the distribution of different pore sizes were analyzed. The results show that large numbers of micropores were distributed between the mesopores and macropores in the shale reservoir, which mainly consisted intergranular pores, intermolecular pores, interlamellar pores of clay minerals, and organic matter skeleton pores. The development of pores smaller than 1 nm was mainly controlled by the clay mineral content, and the development of pores with a size of approximately 1-2 nm was related to the contents of clay minerals and organic matter. These pores could connect the macropores and mesopores well, which is important for gas storage and flow. In this paper, the types, distribution, and main controlling factors of micropores were studied, and our understanding of the reservoir space was improved from the nanometer level to the Angstrom level, which is important for gas storage and flow process analysis.

A rheological and microstructural study of two-step yielding in mud samples from a port area

Natural fine-grained suspensions usually exhibit a complex rheological fingerprint – in particular a two-step yielding phenomenon – due to the presence of mineral clay particles and organic matter (often found in a flocculated state). These rheological properties may vary considerably from one location to another due to the differences in mud composition (specifically in organic matter content). In this study, the origin of this two-step yielding behaviour for natural suspensions is discussed with the help of different experimental techniques including rheology, particle sizing, rheo-optics, and video microscopy. The samples were collected from different locations in the Port of Hamburg, Germany. A rheological analysis of the samples was performed with amplitude sweep, frequency sweep, stress ramp-up and structural recovery tests. The shear-induced structural changes of mud samples was studied by using a parallel plate shearing device with a microscope. Mineral clay-organic matter flocs were studied using video microscopy to obtain the floc size, floc density and settling velocity of flocs. Higher values of rheological properties such as cross-over stress, yield stress, and moduli were observed for samples having higher organic matter content. These samples also produced the largest floc sizes. The rheo-optical analysis showed the formation of cylinder-like structures in fine-grained suspensions upon shearing action, which reflect the origin of two-step yielding behaviour in mud samples, observed in stress ramp-up and amplitude sweep tests. • Mud samples with different TOC content were analysed using rheology. • Two-step yielding was observed in mud from amplitude and stress sweep experiments. • Rheo-optical analysis showed the formation of cylinder-like structure during shearing. • Larger and porous flocs were observed for samples with higher TOC content. • This study provides a useful understanding of mud flocs during shearing.

Variations and geological significance of solid acidity during smectite illitization

Solid acidity is an inherent property of clay minerals and intimately related to the crystal chemistry and structure. Smectite illitization is a common phenomenon in mudstones, during which the variations of solid acidity are our concern. In present study, we prepared samples with different illitization extent and conducted a series of measurements, aiming to figure out the evolution of solid acidity during mineral transformation and draw some inspirations for the impacts of solid acidity on hydrocarbon generation approach and mechanism during illitization. In the early stage of illitization from T-25 to T-250, the morphology is irregular and clay minerals are composed of randomly interstratified mixed-layered mineral (MLM) with total illite layer less than 54%. Brønsted (B) acid sites increase slightly even if smectite layer reduces. The slight reduction of interlayer water and increase of interlayer charge are considered to improve the proton-donating ability of interlayer water. Meanwhile, H3O+ adsorbed by the net structural negative charge also contributes to the increase of B acid sites. For Lewis (L) acid sites, the reduction of octahedral Al, which is caused by incomplete crystallization of illite layers as proved by amorphous particles consisting of Si and Al, controls the decline of L acid sites in early stage. In the late stage from T-300 to T-350, R1 and R2 ordered MLMs are predominant with around 80% total illite layers and regular morphology. B acid sites decrease progressively while L acid sites increase at first and then decrease. The match of reductions of interlayer water and B acid sites indicates the significant reduction of smectite layer turns into the main factor controlling the reduction of B acid sites. Meanwhile, the improvement of the ordering, dramatic increase of total illite layer, and absence of amorphous particles render L acid sites increase. However, further increased crystallinity makes Al bond with hydroxyl groups and thus the decrease of L acid sites. T-450 represents another scenario in which decrease of clay minerals and formation of quartz dilute both B and L acid sites. In summary, the amount, strength, and type of solid acidity are varying constantly in the process of illitization. Random MLMs are favorable for B acid sites while ordered MLMs prefer L acid sites. The acid strength peaks when random MLMs are dominated. B and L acid sites could promote clay-organic matter (OM) interactions via different mechanisms, in this way, variation of solid acidity determines priority of two reaction mechanisms of clay-OM interactions and the composition of the hydrocarbons. In conclusion, the variation of solid acidity during illitization connects the mineral transformation and hydrocarbon generation, affecting the mechanisms of organic-inorganic interactions during hydrocarbon generation and providing implications for further investigation of the organic-inorganic interactions in nature

Influence of Organic Matter Content on Engineering Properties of Clays

Most natural sedimentary clay contains organic matter, and even a small amount of organic matter will have a great impact on the physical and mechanical properties of clay. In order to clarify the influence of organic matter content on clay soil, the illite‐quartz mixture was mixed with natural amorphous peat soil (organic matter content is 50%) in different proportions for studying the influence of different organic matter contents on the physical properties (specific gravity, Gs; moisture content, w; void ratio, e; liquid limit, wL; plastic limit, wp; plasticity index, Ip) and shear characteristics (cohesion, c; friction angle, φ) of clay soil. The experimental results found that, with the change of organic matter content, the specific gravity and void ratio of clay changed linearly, while the water content, Atterberg limit, shear strength, cohesion, and friction angle changed nonlinearly with the increase of organic matter content. Moisture content and Atterberg limit have a turning point when OC = 7.5%. Shear strength, cohesion, and friction angle all have obvious turning points when OC = 7.5% and OC = 37.5%. The variation of moisture content and Atterberg limit with organic matter content indicates that OC = 7.5% may be the limit value for the different forms of organic matter in the clay. When OC ≤ 7.5%, the organic matter in clay is in the bound state; when OC > 7.5%, the bound organic matter reaches saturation; and the free organic matter gradually increases. The change law of shear strength characteristics with organic matter content shows that the interaction between minerals and organic matter exhibits different shear characteristics under different organic matter content. When OC ≤ 7.5%, clay shows mineral properties, when 7.5% < OC ≤ 37.5%, clay shows mineral‐free organic matter properties, and when OC > 37.5%, clay shows free organic matter properties.

Physical and chemical properties, elemental and material snow composition in Rostov-on-Don

To study the current distribution of the heavy metals (HM) levels and iron in the atmospheric precipitation in Rostov-on-Don, an expedition was conducted aimed at simultaneous river water and snow sampling in the Don River, the roadside and park areas. The pH values of the melt-water were characterized by a slightly acidic reaction, and the stale snow in the park had lower values in comparison with the fresh snow. The river water was slightly alkaline, and the concentrations of dissolved migration forms of Pb, Cd, Zn, Ni, Cr, Mn, and Fe did not exceed the MPC. The exception was the Cu content, which exceeded the MPC by 2.4 times. The contents of the dissolved migration forms of Pb, Cd, Zn, Cu, Ni, and Fe in snow exceeded their contents in river waters. The HM and Fe percentage in suspended form in river water and different snow states is calculated and the sequence series are constructed. The analysis showed that in melt-water, in comparison with river water, there is a higher percentage of the HM and iron in the solution. That may be due to the slightly acidic reaction of the snow water medium, which, as is known, promotes the HM and Fe mobilization from the suspension and their transition to the dissolved state. Using electron microscopy and X-ray phase analysis, the suspension composition in the snow of the park zone was studied, which is mainly represented by aggregates of clay minerals, quartz grains, water silicates, feldspars, and organic matter clumps.

Clay Minerals and Organic Matter from Deeply Buried Ordovician-Silurian Shale in Western Iraq: Implications for Maturity and Hydrocarbon Generation

The present work is conducted on the Paleozoic (Ordovician) Khabour and the (Silurian) Akkas shales in the Akkas-1 well of western Iraq. The study is aiming to determine the implications of clay mineral transformation, organic mineral distribution and maturity of hydrocarbon generation, using X-ray diffraction (XRD), scanning electron microscopy (SEM) in addition to organic matter concentrations. In the shale of the Khabour Formation, amorphous organic matter is common and includes various Tasmanite-type organic matter, vitrinite, inertinite, and bituminite. The main clay minerals observed include illite, chlorite, kaolinite, in addition to mixed-layer illite-smectite and rare smectite. In Silurian shale, high content of organic matter is recorded in addition to abundant vitrinite and low content of grainy organic matter (Tasmanites) and pyrite. Illite and kaolinite are commonly found in addition to chlorite and illite-smectite clay minerals. Conversion of smectite to mixed-layer illite-smectite (I-S) and an increase in vitrinite reflectance are commonly observed below 2500 m depth in the studied formations, which coincides with oil and gas generation. These results could be used as an indication of higher maturity and hydrocarbon generation in the deeply buried shale of the Khabour and Akkas formations in western Iraq.

Morphodynamic conditions of heavy metal concentration in deposits of the Vistula River valley near Kępa Gostecka (central Poland)

Abstract The influence of morphodynamics of individual river valley zones on the anthropogenically induced distribution of heavy metals in the Małopolska Gorge of the Vistula River near Kępa Gostecka was studied. Based on the analysis of cartographic and geological mapping data, several floodplain features were distinguished. For each feature, lithological analysis of the deposits was carried out. It comprised determination of clay content, organic matter, carbonates and iron oxides and hydroxides, as well as analysis of heavy metal concentration. The investigations show that the concentration of heavy metals in floodplain surface deposits is strictly linked with the variability of depositional environments, which reflected in the intricate feature pattern. The highest contents of heavy metals have been found in the deposits of the contemporary floodplain, stagnation zones of floodwaters, oxbow lakes buried under floodplain or organic deposits and escarpment foot back swamps, while the lowest in deposits of the Pleistocene terrace and slope wash zones. Variability of floodwater dynamics modelling the floodplain surface is associated with the specific geological setting of the Vistula River valley stretch analysed.

An Advanced Well Log and an Effective Methodology to Evaluate Water Saturation of the Organic-Rich Cambay Shale

Water saturation (Sw) is a vital parameter in the evaluation of hydrocarbon reservoir. Realistic estimation of Sw in shale reservoir is a challenging problem because of the presence of significant clay minerals and organic matter. The present study aims to estimate Sw of organic-rich Cambay Shale, Jambusar–Broach block, Cambay Basin, India, using an effective methodology and improved equation (TOC–clay equation), considering the appropriate corrections to counter the effect of clay minerals and organic matter in modifying resistivity. Advanced log like Litho-scanner has been utilized for the continuous estimation of clay content and total organic carbon (TOC), required for the estimation of Sw. Elemental capture spectroscopy and support vector regression were also applied for evaluation of clay content and TOC in one well where Litho-scanner log is not available. To investigate the effectiveness and applicability of the TOC–clay equation, results of Sw estimated from this equation and various other models have been compared with core Sw for a well. The analysis indicates that Sw derived from TOC–clay equation is having the closest agreement to core Sw data with an average absolute percentage error of 7.9% and coefficient of correlation 0.95. For other models, average absolute errors are significantly higher (16.8–32.7%). The application of TOC–clay equation will be useful for evaluation of the Cambay Shale reservoir. In addition, the resistivity-based TOC–clay equation used in this study is simple with a practical approach; it can be applied easily and efficiently for any organic-rich shale reservoir elsewhere.

Mapping management zones in a sandy pasture soil using an objective model and multivariate techniques

Soils occupied by dryland pastures usually have low fertility but can exhibit a high spatial variability. Consequently, logical application of fertilisers should be based on an appropriate knowledge of spatial variability of the main soil properties that can affect pasture yield and quality. Delineation of zones with similar soil fertility is necessary to implement site-specific management, reinforcing the interest of methods to identify these homogeneous zones. Thus, the formulation of the objective Rasch model constitutes a new approach in pasture fields. A case study was performed in a pasture field located in a montado (agrosilvopastoral) ecosystem. Measurements of some soil properties (texture, organic matter, nitrogen, phosphorus, potassium, cation exchange capacity and soil apparent electrical conductivity) at 24 sampling locations were integrated in the Rasch model. A classification of all sampling locations according to pasture soil fertility was established. Moreover, the influence of each soil property on the soil fertility was highlighted, with the clay content the most influential property in this sandy soil. Then, a clustering process was undertaken to delimit the homogeneous zones, considering soil pasture fertility, elevation and slope as the input layers. Three zones were delineated and vegetation indices (normalized difference vegetation index, NDVI, and normalized difference water index, NDWI) and pasture yield data at sampling locations were employed to check their differences. Results showed that vegetation indices were not suitable to detect the spatial variability between zones. However, differences in pasture yield and quality were evident, besides some key soil properties, such as clay content and organic matter.