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Quaternary mudstone biogas reservoirs in the Qaidam Basin have shown great potential. However, complex pore structures with high clay contents and high heterogeneity limit the understanding of the storage and migration principles of these reservoirs. In this paper, HPMI and nitrogen adsorption experiments, in combination with NMR experiments under water saturation, centrifugation, various drying temperatures and other conditions, were adopted to determine the pore structure characteristics. Specifically, the reservoir space types and pore radius distribution characteristics were clarified. The cutoff values for different types of pores were identified based on the water-saturated mudstone NMR T2 spectra for full aperture distribution scales jointly characterized by mercury injection and nitrogen adsorption experiments. Furthermore, the three pore components and the saturation of different fluids were obtained. The research results indicate that the mudstone biogas reservoir has developed various reservoir spaces, and the pore size is primarily in the micronanometer range. The average total porosity reaches 27.28%, but the proportion of movable water pores is only 9.23% with poor fluid mobility, and the fluids in the pores are mostly capillary-bound water and clay-bound water. Among the different lithologies, argillaceous sand is more likely to become a good production layer. [ABSTRACT FROM AUTHOR]

This study marks the first detailed depositional, diagenetic and organic geochemical investigation of Jurassic Isha Formation in North Waziristan, Khyber Pukhtunkhuwa, Pakistan. Detailed systematic sampling was carried out from exposed outcrop along the Mirali road in North Waziristan for microfacies analysis and diagenetic studies to unravel the depositional environment and diagenetic alterations. The oraganic maturity and hydrocarbon generation potential were assessed by total organic content and Rock-Eval pyrolysis. Outcrop analogue revealed that the formation predominantly comprises of thick to thin bedded oolitic fractured limestone, bioclastic and dolomitic limestone. In the petrography, a total of eight microfacies (MF1–MF8) were constructed and were directed different depositional enviroments. Based on the integrated field data and microfacies analyses, the Isha Formation is interpreted to be deposited on a homoclinal ramp particularly in peritidal, lagoon, and carbonate shoals. Sequences stratigraphic setup shows intervallic Transgressive and Regressive Systems Tracts. The TSTs are mostly grainstone and packstone facies whereas the RSTs are wackestone and mudstone microfacies which demonstrates a single 2nd order cycle and then multiple 3rd order transgressive and regressive cycles for the deposition of Isha Formation. The total organic content and Rock-Eval pyrolysis results were ploted on VanKerevlen diagram which indicate that the source rock potential fall within the type III kerogen. The HI versus Tmax and PI versus Tmax cross plots indicate that the formation lies within the zone of maturation, generation potentiality indicate that the formation has fair to poor potential and hydrocarbons are indigenous. [ABSTRACT FROM AUTHOR]

Red mudstone is a problematic soil that is easily subjected to weathering, disintegrating, and swelling. In this study, a series of large-scale cyclic triaxial tests were performed to investigate the cumulative deformation behavior of red mudstone clay mixed with weathered red mudstone gravel as an improved coarse-grained red mudstone soil (IRMS). The influences of compaction moisture content and confining pressure were investigated. The cyclic loading was applied from 25 to 225 kPa with an increment of 25 kPa and 1,000 or 2,000 cycles for each stage at a frequency of 2 Hz. The experimental results indicate that the strains at the onset of failure are approximately 1% for the optimal moisture content (OMC) with the number of cycles N = 14,000–16,000, and the strains are approximately 1% for the moisture content 2% dry of OMC with N = 12,000–14,000, while the strains exceed 10% for the moisture content 2% wet of OMC with N = 3,000–4,000. The cumulative strain decreases with increasing confining pressure from 20 to 50 kPa, but the influence becomes more significant under higher dynamic stress. A prediction model is proposed for the evolution of cumulative strain under cyclic loading. The IRMS could be used as a construction material for railway subgrade with proper control of field compaction moisture content. [ABSTRACT FROM AUTHOR]

Monitoring the changes in porewater pressure associated with the construction of earthworks can yield information on the stiffness and permeability of the ground, as well as how the natural groundwater regime might be impacted. This paper presents 3 years of porewater pressure measurements in weathered Lias Group mudstone, obtained from a trial cutting and a trial embankment constructed for the UK's High Speed Two (HS2) railway. The immediate changes in porewater pressure were small in relation to the changes in total stress imposed. This can be explained by the consolidation or swelling during the period of construction, combined with the sensitivity of very stiff clays and mudstones to a very small (0.5%) reduction in the degree of saturation. In the longer term, porewater pressures reduced across the site owing to the reduction in ground level at the trial cutting. Rates of porewater pressure change were accelerated by more permeable limestone within the ground profile reducing drainage path lengths. It was concluded that construction-induced porewater pressure changes may be smaller, and their rate of dissipation more rapid, in weathered clays and mudstones such as those of the Lias Group than in younger, more compressible clay deposits. [ABSTRACT FROM AUTHOR]

ABSTRACT The sedimentary fill of Gale crater on Mars is dominated by lacustrine strata that are the focus of investigations into surface processes, climate change and habitability early in the planet's history. This study focuses on the lower part of the explored portion of the Murray formation on Aeolis Mons (Mount Sharp) in the Pahrump Hills and Hartmann's Valley field areas. At Pahrump Hills, sedimentary features and geochemical attributes of exposed mudstones suggest accumulation in an underfilled lake basin in which lake levels, shorelines and salinities fluctuated greatly at various temporal scales. The immediately superjacent stratigraphic interval, designated by the rover team as the Hartmann's Valley member, has previously been interpreted as an aeolian‐deposited sandstone interval. This fresh examination of all available data, however, suggests that the Hartmann's Valley member is strongly dominated by the same mudstone facies that compose most of the underlying Pahrump Hills member. The one novel facies element encountered in the Hartmann's Valley member are undulose bedded to convex bodies of mudstone that are oriented roughly north–south, suggestive of sediment supply from a northern fluvial source. Mudstones analogous in scale and character to these undulose mudstones occur on Earth in multiple modern and ancient lacustrine successions, and are related to deposition of prodelta mud lobes. The mudstones of the Hartmann's Valley member record a continuation of the underfilled evaporitive lake system proposed previously for the underlying Pahrump Hills member but with somewhat more variable environmental conditions. Hartmann's Valley mudstones contain more abundant matrix CaSO4, suggesting more severe evaporitic conditions, whereas the interbedded undulose bedded mudstones signify intermittent freshening and buildout of mud‐dominated deltas into the lake. The textural similarities between Pahrump Hills and Hartmann's Valley strata suggest that the Gale lacustrine system operated at a stable depositional mode with similar environmental parameters during both stratigraphic intervals. [ABSTRACT FROM AUTHOR]

Spatial distribution orientations of blocks can cause significant errors in the discrete element model (DEM) calculation of soil-rock mixture (SRM). To avoid this error, spherical harmonic (SH) series whose harmonization degrees fixed at 15 were proposed for block reconstruction. This research refers to the case-history of a deep excavation rift valley spanning from the Mabian to Zhaojue section of the Leshan-Xichang Expressway, mainly containing moderately-weathered silty mudstone, in the Leshan City, Sichuan Province, China. The appropriate degree of finite-term SH series is selected by the volume, surface area. 100 blocks were scanned on site, and sphericity and angularity of the blocks were calculated. The sphericity and angularity of 50 reconstructed blocks were considered for the error analysis of SH method. Moreover, stochastic polyhedron method was considered for comparing different block reconstructions. The maximum block placement angle was defined to control the spatial distribution orientations of the blocks. Large scale direct tests were carried. Numerical simulations of large-scale direct shear tests were conducted to study the influence of the spatial distribution orientations of the blocks on the mechanical properties of the SRMs. The results revealed that the finite-term SH series fixed at 15 accurately reflected the shape characteristics and mechanical behaviors of actual blocks. The spatial distribution orientations of the blocks had a minimal impact on the friction angle and cohesion of SRM constructed through the SH method. The SRMs developed via the SH method exhibited marginal variations in contact force and anisotropy index of contact across diverse block placement strategies. The evolution of coordination number was closer when employing the SH method under varied block placement methods. Blocks reconstructed by the SH method, could mitigate errors in DEM calculation caused by the spatial distribution orientations of the blocks. [ABSTRACT FROM AUTHOR]

This document introduces a novel equivalent algorithm for forecasting gas content within deep coal seams, which is subject to constraints stemming from the advancements and precision achieved in well and roadway engineering endeavors. This algorithm meticulously acknowledges that coal seam gas content comprises three fundamental components: the inherent gas emission rate of the equivalent stratum, the residual gas content retained within the coal seam itself, and the influence imparted by the gas content within the coal seam. Furthermore, the approach thoroughly considers variations in the level of porosity development within the coal seam and its surrounding rock formations, as well as the occurrence of gas within these structures. The equivalent layer is classified into two distinct groups: the sandstone zone and the clay zone. The sandstone zone utilizes pertinent parameters pertaining to fine sandstone, whereas the clay zone distinguishes between clay rock and thick mudstone. The influencing factor considerations solely encompass natural elements, such as the coal seam's occurrence and geological structure. The residual gas content employs either existing measured parameters or acknowledged experimental parameters specific to the coal seam. Based on this predictive approach, an intelligent auxiliary software (V1.0) for mine gas forecasting was devised. The software calculates the gas content of deep coal seams within the mine at intervals of 100 m × 100 m, subsequently fitting the contour lines of gas content across the entire area. The gas content predictions derived from this equivalent algorithm demonstrate robust adaptability to variations in gas content caused by construction activities, and the prediction results exhibit an acceptable level of error on-site. Notably, the prediction process is not constrained by the progress of tunnel engineering, ensuring that the prediction outcomes can accurately represent the distribution characteristics of deep coal seam gas content. After a year of application, the prediction results have consistently met on-site requirements, providing a scientific foundation for the implementation of effective gas prevention and control measures in the mining area. Furthermore, this approach can effectively guide the formulation of medium- and long-term gas prevention and control plans for mines. [ABSTRACT FROM AUTHOR]

The Jurassic coal-measure source rocks in the Junggar Basin have drawn considerable attention in recent years. In our hydrocarbon thermal simulation experiments of these rocks, we found that the dark mudstone evaluated as good source rock, had a much lower hydrocarbon generation capacity than the coal and carbonaceous mudstone, evaluated as poor source rock. Based on this background, we performed Fourier transform infrared spectroscopy (FTIR) and combined the results of semi-open thermal simulation experiments to explore the association between the molecular structure and hydrocarbon production capacity, with the aim of obtaining a new understanding of hydrocarbon potential of Jurassic coal-measure source rocks from the perspective of molecular structure. The results indicate that coals exhibit lower condensation of aromatic structures and higher relative abundance of aliphatic structures with a higher degree of branched chaining than mudstones and carbonaceous mudstones. Apparent aromaticity (fa), aromatic abundance parameter I, and degree of condensation (DOC) are negatively correlated with organic matter abundance. The aliphatic structural parameter H demonstrates a substantial positive correlation with organic matter abundance. Furthermore, aliphatic relative abundance factor A is associated with the type of organic matter; the better is the type of the organic matter, the larger is the A value. The combination of the molecular structures with the thermal simulation results shows that the aliphatic hydrogen enrichment of selected carbonaceous mudstone is similar to that of coal. However, the relative abundance of the aliphatic group of it is high, and the DOC of the aromatic structure is low, making the hydrocarbon generation base stronger and easier to crack. Thus, the hydrocarbon generation capacity of carbonaceous mudstone is slightly higher than that of coal. Mudstone has low H and I values, and the DOC is high, indicating that its hydrocarbon base is low, so it has low hydrocarbon generation capacity. Therefore, the molecular structure is closely associated with the hydrocarbon potential of coal-measure source rocks. When evaluating the qualities of coal-measure source rocks, the influence of molecular structure on these rocks should be considered. [ABSTRACT FROM AUTHOR]

The exceptionally preserved soft-bodied fossils from the Chengjiang Biota of southwest China have proved to be critical for our understanding of the biodiversity and ecology of the Cambrian explosion of animals. Almost all previously reported soft-bodied Chengjiang fossils are from the event mudstone beds (EB) of the Yu'anshan Formation. Here, we present the first comprehensive investigation of the soft-bodied fossils from the interbedded background mudstone beds (BGB), based on collections made across the past decade, and characterize their preservation. Soft internal cellular organs/tissues, such as digestive tracts and glands, cardiovascular systems, nervous systems, and musculature, are predominantly preserved as carbonaceous compressions, in contrast to their iron oxide-rich preservation in the EB. Our work highlights two distinct preservation modes within a single Burgess Shale-type Lagerstätte, possibly due to the complex interplay of decay, kerogenization, and pyritization. [ABSTRACT FROM AUTHOR]

Low-permeability rock is suitable as the host rock of an underground repository for radioactive waste disposal; however, minor faults might develop there. Investigating the shear capability (= shear compliance) of those faults is crucial because they could be elastically sheared by the thermal effect of the waste to damage the waste's engineered barriers. This study performed constant-head step-injection tests along with a recently developed packer-pressure-based extensometer method for assessing the applicability of this method to investigate the shear capability of minor faults. Herein, two neighboring minor faults (A and B) in siliceous mudstone were evaluated. The results showed that fault A, with centimeter-thick fault breccia, exhibited high shear capability, whereas fault B, with millimeters or less-thick fault breccia, displayed low shear capability despite containing an incohesive fault rock. An elastic shear displacement occurred for fault A during injection and reached 15–66 mm when the test-section pressure increased from 4.1 to 4.3 MPa. Here, the shear capability was 101 mm/MPa or more. Conversely, fault B had cohesion, and no shear displacement was detected even when the test-section pressure increased from 4.0 to 6.0 MPa. In this case, the shear capability was 10−1 mm/MPa or less. The estimated shear capabilities were consistent with the results from previous shear experiments, and therefore, the applied method helps investigate the shear capabilities of minor faults. Highlights: The packer-pressure-based extensometer method was applied to two neighboring minor faults to investigate their shear capability. The estimated shear capability was corroborated with the results from previous shear experiments. The applied method helps investigate the shear capability of minor faults. [ABSTRACT FROM AUTHOR]

Rocks have a softening effect under the long-term physical and chemical action of water, resulting in a reduction in the strength of rock and a weakening of the safety performance of project, which may have destructive effects for the wellbore instability, borehole contraction, leakage, and reservoir protection at a certain time. To investigate the effect of water-induced rock softening on its anisotropy for reservoir protection, the digital experiment was conducted on three types of rocks with four different saturation levels in five different directions. A digital drilling response model was employed to determine the drilling strength and specific energy at the critical point. The drilling parameters of the three types of rocks were recorded to calculate the softening coefficient and the anisotropy of the softening coefficient. The reliability of the proposed anisotropy of the softening coefficient was verified by introducing strength parameters based on the water-induced rock softening. The results show that the softening coefficient decreased with increasing saturation levels. The highest decrease with 43% was observed in mudstone. The anisotropy of the softening coefficient increased with an increasing saturation levels. The highest increase with 12% was observed in mudstone. Both fine-grained sandstone and mudstone exhibited the phenomenon of strength rebound with increasing saturation levels. A comparison with the previous studies reveals that this method can provide a reliable basis for determining the degree of rock softening using drilling strength. Highlights: The effect of water-induced rock softening on rock anisotropy is investigated during drilling process. The digital experiment was conducted on rocks with four different saturation levels. The reliability of the anisotropy of the softening coefficient was verified by introducing strength parameter. [ABSTRACT FROM AUTHOR]

We report the results of organic geochemical analyses of 19 crude oil samples from reservoir sandstones in the 4th Member of the Eocene Shahejie Formation from wells in the Minfeng Sag, Dongying Depression, Bohai Bay Basin (NE China). In addition, 42 Shahejie Formation core samples of dark‐coloured mudstones, including 28 extracts, were analysed. Geochemical data included Rock‐Eval measurements, gas chromatography, GC‐MS and diamondoid analyses. Maceral analyses showed that mudstones in the 4th Member of the Shahejie Formation ("Es4") contain Types I and II1 kerogen. The member can be divided into upper (Es4s) and lower (Es4x) intervals. Oil‐prone Es4s rock samples have good to excellent hydrocarbon‐generating potential based on calculated initial TOC values; Rock‐Eval Tmax values indicate that they are sufficiently mature for hydrocarbon generation. Analytical results suggest that both Es4s and Es4x mudrocks are potential source rocks for oils produced at fields in the Minfeng Sag. Analysed crude oils from the Minfeng Sag were classified into three genetic groups. Group I oils are mature to highly mature and have undergone a moderate degree of thermal cracking. They are characterized by a low β‐carotane/nC25 ratio and C30 4‐methylsterane index (4MI); high values of oleanane index (oleanane /C30‐hopane), C27 diasterane/C27 regular sterane (C27Dia/C27), regular sterane/17α hopane and gammacerane/C30 hopane (G/H); and medium pristane/phytane ratios (Pr/Ph). This suggests that Group I oils are mostly derived from source rocks in the upper part of the Es4x unit which are interbedded with evaporites. Group II oils are mature and have high 4MI and Pr/Ph ratios, low oleanane index, regular sterane/17α hopane and C27Dia/C27 ratios, and mediumβ‐carotane/nC25 and G/H. These features are similar to those of Es4s source rocks, indicating their genetic correlation. Group III oils show the lowest maturity and highβ‐carotane/nC25 and regular sterane/17α hopane, and low oleanane index, Pr/Ph and 4MI. Previously‐published data indicates that oils similar to those in Group III were mainly sourced by Es4s mudstones. [ABSTRACT FROM AUTHOR]

The Mamonia Mélange in the Ayia Varvara area (southwestern Cyprus) is characterized by a matrix supported mélange which is composed of tectonized siltstones and mudstones with numerous blocks that were derived from the Mamonia Allochthonous Complex (Petra tou Romiou Formation reefal limestones, Phasoula Formation volcanics, Kholetria Member pelagic limestones, Akamas Member sandstone, Parekklisha Member sandstone, Ayia Varvara Formation metamorphics and Episkopi Formation radiolarian cherts). Subordinate blocks were derived from the Troodos Ophiolite Complex: serpentinites, gabbro, pillow lavas and cherty umbers (Perapedhi Formation). Radiolarian assemblages from chert blocks display a broad spectrum in age, ranging from the Late Triassic (latest Carnian–early Norian) to the youngest Cenomanian. The composition of the mélange in the Ayia Varvara area differs from the one described in the Petra tou Romiou area (SW Cyprus), as various lithologies were recorded (like Akamas Member sandstone and Parekklisha Member sandstone) which were not detected previously. The Mamonia Mélange was formed during the Late Cretaceous, most probably after the end of deposition of the Perapedhi Formation (late Santonian–early Campanian). [ABSTRACT FROM AUTHOR]

The hydro-mechanical behaviour and the constitutive model of sandy mudstone were investigated in this article. Two groups of hydro-mechanical triaxial compression tests were conducted. The results indicated that the inelastic deformation, damage, permeability and failure of the sandy mudstone were affected by the pore pressure and confining pressure. The hydro-mechanical behaviour was characterised by the coupled elastoplastic damage model. This model was based on the effective stress principle and numerical return mapping algorithms. Sensitivity analysis was also performed to examine the effects of four key parameters on the modelling of elastoplastic and damage behaviour. This study can provide a foundation for physical understanding and mathematical modelling of sandy mudstone under coupled loads. [ABSTRACT FROM AUTHOR]

The remains of a unique fossil bony fish were discovered in late Eocene (39.1–36.7 Ma: NZ Kaiatan stage) mudstone at Burnside near Dunedin, New Zealand in the 1930s and subsequently named and described by Frederick Chapman. He interpreted the type specimen as being a large-scaled relative of the modern Thyrsites of the Gempylidae (Scombroidei: Trichiuroidea), known to be swift, large oceanic predators. However, Chapman is unlikely to have seen all of the fossil, and did not discuss the skull and caudal skeleton. Additional material now allows these to be included in the expanded description herein, including key morphologic features of the fish such as the presence of premaxillary fangs. This study describes the rather complex history of the specimen and re-examines this significant fossil fish in the University of Otago collections, giving a more complete understanding of Eothyrsites morphology, paleoecology and relationships. In summary, we suspect Eothyrsites represents an ancestral form of gempylid, closely related to the gemfish group, an important Southern Hemisphere macrofossil record from the Eocene seas around Zealandia. [ABSTRACT FROM AUTHOR]

Based on sedimentary characteristics of the fine-grained rocks of the lower submember of second member of the Lower Cretaceous Shahezi Formation (K1sh2L) in the Lishu rift depression, combined with methods of organic petrology, analysis of major and trace elements as well as biological marker compound, the enrichment conditions and enrichment model of organic matter in the fine-grained sedimentary rocks in volcanic rift lacustrine basin are investigated. The change of sedimentary paleoenvironment controls the vertical distribution of different lithofacies types in the K1sh2L and divides it into the upper and lower parts. The lower part contains massive siliceous mudstone with bioclast-bearing siliceous mudstone, whereas the upper part is mostly composed of laminated siliceous shale and laminated fine-grained mixed shale. The kerogen types of organic matter in the lower and upper parts are types II2-III and types I-II1, respectively. The organic carbon content in the upper part is higher than that in the lower part generally. The enrichment of organic matter in volcanic rift lacustrine basin is subjected to three favorable conditions. First, continuous enhancement of rifting is the direct factor increasing the paleo-water depth, and the rise of base level leads to the expansion of deep-water mudstone/shale deposition range. Second, relatively strong underwater volcanic eruption and rifting are simultaneous, and such event can provide a lot of nutrients for the lake basin, which is conducive to the bloom of algae, resulting in higher productivity of types I-II1 kerogen. Third, the relatively dry paleoclimate leads to a decrease in input of fresh water and terrestrial materials, including Type III kerogen from terrestrial higher plants, resulting in a water body with higher salinity and anoxic stratification, which is more favorable for preservation of organic matter. The organic matter enrichment model of fine-grained sedimentary rocks of volcanic rift lacustrine basin is established, which is of reference significance to the understanding of the organic matter enrichment mechanism of fine-grained sedimentary rocks of Shahezi Formation in Songliao Basin and even in the northeast China. [ABSTRACT FROM AUTHOR]

The practice of oil and gas exploration has confirmed the existence of recoverable shale oil resources in the Permian Lucaogou Formation on the northern edge of the Bogda Mountains. However, previous research on the development characteristics and main controlling factors of shale oil resources in this area is relatively limited. In order to elucidate the development characteristics and principal controlling factors of the shale deposit in the Lucaogou Formation, the characteristics, physical properties, diagenesis, and influencing factors of the shale ore were investigated utilising data derived from outcrop, drilling, seismic, and geochemical analysis. The findings indicate that the shale of the Lucaogou Formation is prevalent and extensive. The deposit's lithology is predominantly composed of dark grey and grey-black mud shale, interspersed with thin layers of dark grey and grey-black sandy mud shale and dolomite mud shale. The most prevalent minerals are carbonate minerals, followed by feldspar and quartz, with a notable proportion of brittle minerals. The deposit is primarily composed of dissolution pores, bedding fractures, and structural fractures, with a porosity of 1.23–3.26% and permeability of 0.012–0.076 mD, which are characteristic of ultra-low porosity and ultra-low permeability deposits. Among the three deposit types, the sandstone type exhibits the most favourable physical properties, followed by the dolomite type and the shale type, which displays the least favourable properties. The shale of the Lucaogou Formation is currently in the middle diagenetic phase, which is characterised by compaction, cementation (carbonate cementation, mudstone cementation, pebble cementation), and dissolution. The destructive effect of compaction and cementation on the physical properties is counterbalanced by the constructive effect of dissolution. The diagenetic environment has gradually changed from an alkaline environment to a slightly alkaline, slightly acidic stage. [ABSTRACT FROM AUTHOR]

Colored asphalt pavements have been implemented in South Korea to enhance visibility and lane distinction; however, color fading, accelerated deterioration, and increased pothole occurrence have been noticed. As a solution, alternative materials that can be used for the construction of colored asphalt pavements are being explored. This study evaluates the feasibility of using mudstone aggregate in constructing colored asphalt pavement in South Korea. Initially, aggregate quality tests were conducted on mudstone samples to assess their suitability compared to standard criteria. To enhance the visibility and color retention of colored asphalt, addition of pigment in the colored asphalt pavement mixture was considered and evaluated. The asphalt mixtures were evaluated for deformation, crack and viscoelastic properties using the Kim test, indirect tensile (IDT) strength test, and dynamic modulus test, respectively. Results showed that mudstone aggregate exceeded quality standards and the colored asphalt mixtures demonstrated superior deformation strength and crack resistance compared to typical SMA. However, the addition of pigment slightly reduced these properties. Overall, the findings suggest mudstone aggregate as a viable alternative for constructing colored asphalt pavements, offering potential improvements in durability and color retention. [ABSTRACT FROM AUTHOR]

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Terrestrial sedimentary basins are influenced by rapid changes in the clay content, resulting in significant differences in the lateral sealing capacity (shale gouge ratio, SGR) of different parts of the fault. In the present study, we used a method of setting virtual wells and using seismic inversion data to accurately calculate the SGR of faults in strata composed of interbedded sandstone and mudstone calculate the clay content of the strata and to compensate for the low level of the actual well control. Optimal well spacing was determined based on the variable clay content of the formation. The planar variation of the fault throw was characterized via seismic interpretation. We also examined the lateral sealing of faults. The Putaohua oil layer in the S14 area of the Sanzhao Sag in the Songliao Basin was chosen as an case study. Based on the calculation of fault SGR values and the oil distribution, the evaluation criteria for the fault sealing capacity were determined, and the changes in the lateral sealing capacity of the faults were analyzed. This approach accurately estimates fault SGR values and predicts the effective oil-bearing area within the fault zone. It is also suitable for evaluating the lateral sealing of faults in strata composed of interbedded sandstone and mudstone. Our findings provide an in-depth understanding of the lateral sealing of faults and can aid in further research on petroleum distribution patterns. [ABSTRACT FROM AUTHOR]

At geologic timescales, a significant proportion of the sediment eroded from continents is transferred from rivers to littoral cells, then through submarine canyons to deep ocean basins. Accumulation and occasional discharge of sediment from canyon headwall regions is a likely driver for the sediment gravity flows believed to be responsible for much of this mass transport, but the responsible mechanisms and event timescales in canyon heads are imprecisely defined, largely due to the drowning of canyon heads since the last glaciation and the resulting dearth of modern depositional environments to observe. We investigated a littoral cell adjacent to Mattole submarine canyon in Northern California to better understand the influence of bathymetry and coast shape on sediment trajectories and hypothesize that canyon heads promote littoral sediment accumulation due to bathymetric sheltering of the adjacent coast from waves and convergence of littoral cells exposed to varying wave direction. The uppermost gullies of Mattole Canyon extend to the littoral cell, and a train of sediment waves within the uppermost thalweg of Mattole Canyon suggests that gravity-driven flows of shore-derived sediment may have recently occurred. Mattole Canyon and nearby Mendocino Canyon flow into the deep Mendocino Channel, which has the highest observed Late Holocene sediment accumulation rates in Northern California. We documented the beach slope, grain size, and sediment provenance along 15 km of coast adjacent to Mattole Canyon and conducted numerical wave modeling to infer the dominant direction and magnitude of sediment transport, relative wave sheltering by bathymetry, and estimated sediment mobility in the vicinity of the canyon head over a multi-year period. South of the canyon headwall, in the vicinity of the Mattole River outlet, coarser sediment rich in metasandstone clasts and steeper beach slopes coincide with decadal-scale beach accretion. North of the canyon head, sediments are generally finer, beaches are flatter, clast lithologies include more quartz and mudstone grains, and there is decadal-scale net erosion. Wave modeling suggests the Mattole headwall region is subject to sustained sheltering from waves due to canyon bathymetry, littoral sediment convergence above the canyon head for much of a typical year, and occasional bed entrainment of sediment in the canyon's uppermost gullies by large waves. Larger winter waves from the northwest likely result in net southerly drift north of the canyon head, with a high likelihood of preferentially transporting fine-grained, more quartz-rich sediment towards the Mattole headwall. Smaller summer swells from the west and south likely results in net northerly transport of metasandstone clast-rich Mattole River-derived sediment towards the canyon head. The imbalance in seasonality in wave conditions, coast shape, and sediment delivery by the Mattole River and other coastal creeks is broadly consistent with the spatial patterns in grain size, mineralogy, slope, and beach width that we observe in the vicinity of the canyon, and the net delivery of sediment to the Mattole Canyon head. An approximate mass balance of sediment flux from coastal streams feeding Mattole River littoral cell suggests that sediment volumes likely accumulate in the canyon headwall region that could supply several density flow events in a typical decade. These findings highlight the importance of the connectivity of the canyon to the nearshore region for the processes and products in canyons and fans. We hypothesize that feedbacks between canyon bathymetry, sediment accumulation, and mass evacuating flows promotes the long-term persistence of canyon systems. [ABSTRACT FROM AUTHOR]

Design for inefficient well sidetracking of Bohai oilfield increased greatly recent years. Optimize sidetracking programs and reduce costs is important. Trajectory and window sidetracking tools were optimizing chosen for middle depth sidetracking to reduce costs. Horizontal casing well could solve mudstone and water contain problems for same layer sidetracking. For open hole completion well, window sidetracking costs lower for drilling platform working, and open hole sidetracking is suitable for workover rig. One to one design method for inefficient well sidetracking could reduce costs efficiently, good application results have been obtained. [ABSTRACT FROM AUTHOR]

The high exploration and development production capacity of the Jiyang Depression, Bohai Bay Basin, China in the early stage confirms the huge exploration and development potential of shale oil in the study area. Due to the complexity of the depositional mechanism in the study area, the distribution law of fine-grained sedimentary rocks is not well understood, which restricts further exploration breakthroughs. This paper comprehensively observes rock cores and thin sections, combines mineral components, Rock-Eval pyrolysis, rock-cutting logging and logging data to classify lithofacies, and clarifies the distribution law of various lithofacies. The research results show that, according to lithological characteristics, various lithofacies origins are classified into three categories: terrigenous, mixed, and endogenous sources, and six lithofacies types are distinguished: terrigenous low-organic-matter massive siltstone (LF1), terrigenous low-organic-matter massive mudstone (LF2), mixed-source medium-organic-matter massive mudstone (LF3), mixed-source medium-to-high-organic matter laminated-massive mudstone (LF4), mixed-source medium-to-high-organic-matter laminated mudstone (LF5), and endogenous-sourced medium-to-high-organic matter laminated limestone (LF6). The distribution of lithofacies in plane is symmetrical in the east–west direction and is characterized by a banded distribution; the distribution in profile shows a stable depositional process and a continuous depositional sequence. The various lithofacies depositional models have been summarized; the terrigenous input from the northern steep-slope zone has influenced the hydrodynamic conditions of the lake basin, significantly affecting the lithofacies depositional variations from the steep-slope zone to the deep-sag area. The geological evaluation of each lithofacies has been conducted; LF1 + LF4 + LF5 are classified as Class I—target reservoirs for shale oil development, while LF3 + LF6 are considered Class II—favorable reservoirs. The result of the study provide a reference for the classification of fine-grained sedimentary-rock facies and distribution characteristics, and the evaluation of shale-oil-reservoir sweet spots in graben lake basins. [ABSTRACT FROM AUTHOR]

The Qaidam Basin is the largest sedimentary basin within the Tibetan Plateau, with up to ∼15-km-thick deposits accumulated in the Cenozoic. Understanding how it deformed in response to the far-field effects of India-Eurasia collision is critical to improving our knowledge of the mechanism underlying northward plateau growth. Unlike typical compressional basins, where upper-crustal deformation concentrates at their margins, the Qaidam Basin features the development of many NW- to WNW-striking folds across the entire basin. Why crustal shortening occurred in the interior of Qaidam Basin, ∼100 km away from the margins, together with the underground geometries beneath these folds, remains unknown. Herein, based on newly acquired three- and two-dimensional (3-D and 2-D) seismic reflection data, borehole logging, and scaled physical analog modeling, we investigated the geometries, kinematics, and formation mechanisms of the folds within the interior of Qaidam Basin. For the first time, we reveal three local weak layers in the Lulehe, Upper Xiaganchaigou, and Shangyoushashan Formations, respectively. They consist mainly of mudstone intercalated with evaporites and limestones, and they have different spatial distributions that are likely confined by major faults and folds. These mechanically weak layers became locally thickened or thinned in response to tectonic loading and/ or facilitated detachment slip to form many décollement folds that were observed at the surface. The shallow deformation above the weak layers is largely decoupled from underlying basement-involved faulting and folding, which mostly terminate upward in these weak layers. Analog modeling results suggest that the lowermost and widely distributed décollement layer in the Lulehe Formation likely facilitated long-distance rapid propagation of deformation into the basin interior. In sum, our study highlights the significance of multiple weak layers during Cenozoic deformation in the Qaidam Basin interior. [ABSTRACT FROM AUTHOR]

Based on the orthogonal test design method, the expansive mudstone in the cutting of Jingxin expressway in Zhangjiakou city was tested, and the relationship between the expansion rate of mudstone samples under different overlying loads and the soaking time, initial water content and compaction degree was studied, and the sensitivity of various factors was analyzed by the range analysis method. The results showed that the curve of expansion rate with the soaking time presented an S-shaped trend, which can be roughly divided into initial expansion stage, accelerated expansion stage and slow expansion stage. Under the same initial water content, the expansion rate increased with the increase of the compaction degree. Under the same compaction degree, the expansion rate decreased with the increase of initial water content. The range analysis method showed that the soaking time of the sample was the main factor affecting the expansion rate. Water content and compaction degree were the secondary influencing factors, and the influence of water content on the sample expansion rate was obvious under small load, and the load continued to increase, the compaction degree exceeded the influence of water content on the sample expansion rate. [ABSTRACT FROM AUTHOR]

A deep-marine sedimentary succession of Whaingaroan to Altonian age (Early Oligocene–Early Miocene), cropping out near Weber, southern Hawke's Bay, records abrupt changes in depositional paleoenvironments and sedimentary lithofacies. Highly calcareous early Waitakian (latest Oligocene) Weber Formation (Mangatu Group/Waka Supergroup) is unconformably overlain by terrigenous-dominated late Waitakian–Otaian (Early Miocene) Coast Road or Whakataki formations (Tolaga Group/Māui Supergroup). Most notably, in some localities, lowermost parts of the Coast Road Formation (Mangapuku Mudstone Member) contain prominent matrix-supported extra-formational olistoliths of centimetre to decametre scale derived from the underlying Weber Formation. Deposition of these blocks is attributed to deep-water collapse of parts of rapidly growing, over-steepened, reverse-fault-controlled thrust ridge(s). The onset of Coast Road and Whakataki formation deposition and associated abrupt changes in sedimentary lithofacies correlate to prominent Early Miocene lithological, mineralogical, and paleoenvironmental changes elsewhere along the Hikurangi Margin. We attribute these bio- and lithostratigraphic changes as evidence for significant shortening and upper-plate reverse faulting marking the onset of subduction beneath eastern North Island during the mid-Waitakian (c. 23 Ma). Proposed lithostratigraphic revisions presented herein help clarify depositional events and correlative sedimentary packages within the Miocene Hikurangi margin. [ABSTRACT FROM AUTHOR]

Studying the mechanical properties and failure mechanisms of damaged rocks holds practical significance in guiding tunnel or roadway support and assessing the stability of engineering rock masses. To uncover the failure mechanisms of sandy mudstone with varying degrees of damage, we conducted cyclic loading‐unloading tests to create specimens at different damage levels. Subsequently, uniaxial loading tests were performed to investigate the fundamental mechanical properties, wave velocity, and acoustic emission (AE) parameter evolution characteristics of the damaged specimens. The classification of damaged rocks was based on the energy evolution characteristics of damaged sandy mudstone. Finally, we discuss the damage and deterioration mechanisms of different types of sandy mudstone. The findings contribute to establishing a theoretical foundation for evaluating the degree of rock damage. Highlights: The damage degree of rocks was calculated according to the dissipated energy.The response characteristics of AE parameters of damage samples were revealed.The classification of damaged samples is based on the mechanical parameters. [ABSTRACT FROM AUTHOR]

The current extension limit prediction model for offshore extended-reach well (ERW) in mudstone does not consider the formation collapse, which poses a huge risk to offshore drilling construction. To address this problem, this paper presents new open-hole extension limit prediction model for ERW. By considering formation collapse, rate of penetration (ROP), and annular pressure loss, the extension limit models during normal drilling and tripping were derived. The sensitivity of geological and engineering factors was evaluated by analyzing limits for wells 1H and 2H. The research results showed that: (1) The extension limit increases with the ROP and formation collapse duration, but decreases with the increase in mud weight, plastic viscosity, and flow rate. (2) In ERWs, the mud flow rate has a significant impact on the extension limit than the plastic viscosity of mud fluid. However, mud weight has the least impact compared to the two. (3) Considering various parameters, the predicted extension limit of well 1H, when the mud weight is 1.16 g/cm3 [9.67 ppg], is 1593.28 m [5225.96 ft] less than the limit when the collapse period is not considered. [ABSTRACT FROM AUTHOR]

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In this study, FDEM (ECZM), which is the combined finite-discrete element method (FDEM) based on an extrinsic cohesive zone model (ECZM), was improved by incorporating a novel algorithm that makes it easier to insert the cohesive elements than the conventional adaptive remeshing and a scheme to avoid the generation of dormant cohesive element, which is generated as a result of inserting a single cohesive element within the FDEM mesh. The improved FDEM (ECZM) was implemented in a self-developed 2-dimensional code, and it was first validated against a numerical experiment assuming a virtual rock. Subsequently, the proposed FDEM was applied to model the uniaxial compression and the Brazilian tests of siliceous mudstones under quasi-static loading. The results of the proposed FDEM simulations reasonably captured the trends of fracturing and stress-strain curves observed in the experiments well. The proposed scheme can also be extended to parallel computation based on general-purpose-graphic-processing-unit (GPGPU) and 3-dimensional FDEM (ECZM) with minimal efforts. [ABSTRACT FROM AUTHOR]

An increasing number of geological hazards along high-speed railways on the Qinghai–Tibetan Plateau have occurred and have resulted in a profound influence on old infrastructure, which has attracted increasing attention. The landslide event that occurred on September 15, 2022, in Jiujiawan village, Xining city, Qinghai Province, is a typical case. Based on field investigations and remote sensing interpretations, a comprehensive analysis was conducted on the landslide. Additionally, the potential secondary failure of the current Jiujiawan landslide was assessed using Fast Lagrangian Analysis of Continua in Three Dimensions (FLAC3D). Based on the application of the small baseline subset-interferometric synthetic aperture radar (SBAS-InSAR) technique to SAR images from February 24, 2017 to September 14, 2022, a significant westward horizontal deformation was found to have been formed prior to the occurrence of the landslide. The maximum annual average deformation rate in the line of sight (LOS) direction reached −45 mm/yr, with a maximum cumulative deformation of −178 mm. This value was consistent with the continual increase in annual precipitation (2.51 mm/yr) prior to the occurrence of the landslide. The accumulated precipitation before the landslide was 279.8 mm, accounting for 54.2% of the total annual precipitation, with a particularly notable surge in monthly precipitation observed during August (250.3 mm). Additionally, the occurrence of a seismic event with a magnitude of Ms 6.9 in Menyuan County, 80 km away from Xining, could be a potential triggering factor to the landslide, as evidenced by an abrupt subsidence alteration observed prior to and following the earthquake. The maximum subsidence in the line of sight (LOS) direction exceeded 11 mm, exhibiting a highly consistent spatial distribution with the occurrence range of landslides. These results suggest that the Jiujiawan landslide was likely induced by earthquake events in the early stage and heavy rainfall in the later stage. The FLAC3D numerical simulation show that after the landslide, the slope remained marginally stable under natural conditions; however, it is susceptible to reactivation with heavy rainfall. [ABSTRACT FROM AUTHOR]

Abstract Planar lamination is a ubiquitous component of modern and ancient fine‐grained sediments deposited by subaqueous sediment gravity flows. These sediments commonly exhibit alternating sub‐millimetre‐thick, sharply bounded silt‐rich and clay‐rich layers that change little in thickness or sediment texture over lateral distances that range up to at least several tens of metres. Silt‐rich layers are moderately to well‐sorted and a few tens to hundreds of microns to a single silt‐grain thick. In contrast, clay‐rich layers are more poorly sorted, and a few tens to hundreds of microns thick. The thickness and regular alternation of these texturally differentiated interlayers, in addition to the absence of features suggesting transport bypass or deposition by migrating rugged bed forms, suggest alternating physical processes and related modes of deposition in the near‐bed region immediately above the bed. Previous interpretations have focussed on clay flocculation, which is difficult to reconcile with the high fluid shear conditions in the near‐bed region. Here it is suggested that in the millimetre to sub‐millimetre‐thick viscous sublayer at the base of a hydraulically smooth turbulent flow, a combination of high fluid shear and sediment concentration initially leads to shear thinning and enhanced mobility in the lower part of the flow, and for silt to continue settling to the bed forming a well‐sorted silt lamina. As silt settles and clay‐size sediment increases in concentration, hydrodynamic lubrication forces strengthen and reduce mobility of the near‐bed part of the flow. This condition is then perturbed by a bedward‐directed outer flow disturbance that dramatically increases frictional stresses and effective fluid viscosity and ultimately shear jamming that causes gelling and deposition of a poorly sorted clay‐rich layer. This process is then repeated multiple times to build up a deposit composed of alternating silt‐rich and clay‐rich laminae overlain by structureless mud deposited directly from suspension.

Aiming at the design problem of inclined borehole wall in expansive mudstone formation in eastern Mongolia, a theoretical model of circular borehole wall under the combined action of uneven ground pressure and expansive contact pressure is established based on elastic mechanics theory. The analytical solution of borehole stress and displacement under the combined action of uneven ground pressure and expansive contact pressure is obtained. The influence of wall thickness on wall stress and displacement is studied. Based on the thermal coupling module of FLAC3D, the optimization scheme of different shaft thickness is simulated, and more reasonable supporting parameters are determined by optimizing shaft section and supporting form. The numerical results show that when the outer shaft wall reaches 600 mm and the inner shaft wall reaches 600 mm, the influence of increasing the shaft wall thickness on the displacement and deformation is not obvious. The optimized support scheme can effectively resist wellbore deformation in expansive mudstone formation.

The injectability of mudstone is a key parameter for grout modification and is affected by hydration. Inherent injectability is predominantly determined by pore size distribution nuances, encompassing both the critical pore size and the heterogeneity inherent within the pore structure. In this study, low-field nuclear magnetic resonance technology is employed to delineate the transverse relaxation time distribution curves amidst the hydration process of three distinct clay rocks, namely kaolinite, illite, and montmorillonite. The evolution characteristics of permeability are assessed, leveraging the Schlumberger-Doll research model. It is ascertained that a prolonged hydration reaction (98 days) engenders a self-healing effect pertinent to rock permeability. A comprehensive analysis unveils the impacts rendered by various types of clay minerals and distinct durations of hydration upon the characteristic distribution of rock pore sizes. The diffusion and seepage pores are distinguished based on a pore diameter boundary of 100 nm, and the time-varying characteristics of their heterogeneity are studied based on fractal theory. The research results show that for rocks without clay minerals, the injectability reaches and basically maintains 11% unchanged after being soaked for 9 days. For rocks containing kaolinite, the injectability reaches and basically maintains 3.4% unchanged after being soaked for 42 days. For rocks containing illite, the injectability reaches a maximum of 0.9% after being soaked for 56 days, then slowly decreases to 0.6%. For rocks containing montmorillonite, the injectability reaches and remains unchanged at 7.8% after being soaked for 28 days. Combined with the time-varying characteristics of the fractal dimension of seepage pores, the heterogeneity of seepage pores weakens, so the pore structure evolution caused by the hydration of clay minerals has a beneficial effect on the injectability of muddy rock masses.

In this study, an innovative breakthrough pressure detection system for shale oil is introduced. Experiments were conducted on source rocks from three main rock types in the upper member of the Lower Ganchaigou Formation in the Western Qaidam depression, in Qinghai, China. The results show that the differences between the breakthrough pressures of laminated calcareous mudstone (LCM), siltstone (SS), and massive mixed mudstone (MMM) in the formation are of several orders of magnitude. In particular, the shale oil breakthrough pressure of laminated calcareous mudstone is more than five times greater in the vertical bedding direction than in the horizontal bedding direction. As black medium shale oil turns into yellow light shale oil, the breakthrough pressures in the same lithology and direction are reduced by two-thirds. In laminated mudstone the horizontal breakthrough pressure is lower than the vertical, while in massive mixed mudstone the vertical breakthrough pressure is lower. A composite migration model for shale oil in hybrid strata—horizontal migration along bedding and vertical migration through micro-fractures—is proposed. The results are of great significance for understanding the accumulation of shale oil and for identifying exploration targets. [ABSTRACT FROM AUTHOR]

Abstract Mudstones and shales serve as natural barrier rocks in various geoenergy applications. Although many studies have investigated their mechanical properties, characterizing these parameters at the microscale remains challenging due to their fine-grained nature and susceptibility to microstructural damage introduced during sample preparation. This study aims to investigate the micromechanical properties of clay matrix composite in mudstones by combining high-speed nanoindentation mapping and machine learning data analysis. The nanoindentation approach effectively captured the heterogeneity in high-resolution mechanical property maps. Utilizing machine learning-based k-means clustering, the mechanical characteristics of matrix clay, brittle minerals, as well as measurements on grain boundaries and structural discontinuities (e.g., cracks) were successfully distinguished. The classification results were validated through correlation with broad ion beam-scanning electron microscopy images. The resulting average reduced elastic modulus (E r ) and hardness (H) values for the clay matrix were determined to be 16.2 ± 6.2 and 0.5 ± 0.5 GPa, respectively, showing consistency across different test settings and indenter tips. Furthermore, the sensitivity of indentation measurements to various factors was investigated, revealing limited sensitivity to indentation depth and tip geometry (when comparing Cube corner and Berkovich tip in a small range of indentation depth variations), but decreased stability at lower loading rates. Box counting and bootstrapping methods were applied to assess the representativeness of parameters determined for the clay matrix. A relatively small dataset (indentation number = 60) is needed to achieve representativeness, while the main challenges is to cover a representative mapping area for clay matrix characterization. Overall, this study demonstrates the feasibility of high-speed nanoindentation mapping combined with data analysis for micromechanical characterization of the clay matrix in mudstones, paving the way for efficient analysis of similar fine-grained sedimentary rocks.

Abstract In order to investigate the macroscopic and mesoscopic mechanism of hydration instability of rock-grout structure under the influence of moisture content, a direct shear test combined with particle flow code (PFC) simulation was conducted subject to various moisture content levels and normal stresses. The results show that a higher moisture content would compromise the load bearing capacity of soft rock anchorage structures by deteriorating the structural integrity of the surrounding rock and the bonding effect between the anchorage interfaces. The load bearing capacity of the surrounding rock is also rapidly reduced. The rock-grout structure has four main shear damage modes, which are influenced by both moisture content and normal stress. When the saturated moisture content is reached, the anchorage structure has lost its bearing capacity, and the rock is muddied and subsequently debonded from the bolt. The energy required to break the internal adhesion of the rock-grout structure under the effect of hydration is greatly reduced, resulting in easy decoupling and dispersion between the rock skeleton particles. In turn, the rock surface particles bonded by the anchor agent are separated from the deeper particles, resulting in the failure of the bonding surface and weakening the coupling effect between the anchor and the surrounding rock. According to the test results, the control measures for surrounding rock of muddy roadway are put forward.

The Chang 6 sandstone reservoir of the Upper Triassic Yanchang Formation in the Ordos Basin is one of the tight-oil-rich intervals in the basin. Owing to the strong heterogeneity and complex lithology of the Chang 6 reservoir, lithology and fluid identification have become more challenging, hindering exploration and development. This study focused on the Chang 6 member in the Qingcheng area of the Ordos Basin to systematically analyze the lithology, physical properties, and oil-bearing properties of the Chang 6 reservoir. We adopted the method of normalized superposition of neutron and acoustic time-difference curves, the method of induced conductivity–porosity–density intersection analysis, the method of superposition of difference curves (Δφ), and the induced conductivity curve. Our results indicated that the method of normalized superposition of neutron and acoustic wave time-difference curves could quickly and effectively identify the lithologies of tight fine sandstone, silty mudstone, mudstone, and carbonaceous mudstone. The induced conductivity–porosity–density cross-plot could be used to effectively identify oil and water layers, wherein the conductivity of tight oil layers ranged from 18 to 28.1 mS/m, the density ranged from 2.42 to 2.56 g/cm3, the porosity was more than 9.5%, and the oil saturation was more than 65%. Based on the identification of tight fine sandstone using the dual-curve normalized superposition method, the oil layer thickness within the tight fine sandstone could be effectively identified using the superposition of difference curves (Δφ) and induced conductivity curves. Verified by oil-bearing reservoir data from the field test, the overall recognition accuracy of the plots exceeded 90%, effectively enabling the identification of reservoir lithology and fluid types and the determination of the actual thickness of oil layers. Our results provide a reference for predicting favorable areas in the study area and other tight reservoirs. [ABSTRACT FROM AUTHOR]

Water inrush from separation layers is a special type of water inrush disaster that occurs during coal mining. It is characterized by the absence of precursors before the inrush, a sudden and massive influx of water, strong destructive power, and significant difficulty in prevention and control. This disaster causes substantial economic losses and casualties in mines. To study the dynamic evolution characteristics of the overlying rock strata in Guojiahe coal mine, field investigations, theoretical analysis, physical simulations, and numerical simulations were conducted. The development state of the overlying rock strata and the height of the water-conducting fractures in the 1304 working face during continuous mining were analyzed, and the spatial position of the strata where water hazards could form was determined. Through theoretical calculations, the height of the water-conducting fracture zone was found to be approximately 205 m, forming a water-storable separation space about 248 m above the coal seam roof. A physical similarity model was constructed to study the development state of overlying rock strata separation in the 1304 working face. Experimental results indicate that, as the working face advances, the rock strata gradually develop lateral separation spaces from bottom to top, and vertical fractures increase progressively in a similar manner. The spaces and fractures formed in the early stages of the working face advance gradually close and form a compaction zone. However, new fractures develop near the working face side. As mining continues, the asynchronous movement of the overlying rock promotes the development of vertical fractures, providing water-conducting channels for water inrush from the separation. Based on numerical simulation analysis of the development state of overlying rock strata separation and the height of the water-conducting fracture zone, it can be concluded that the water-storable separation space develops between the 8th layer of the formation of sandy mudstone and the 9th layer of the Yijun Formation conglomerate, which is 248 m from the coal seam roof. When excavated to 280 m, the separation space reaches its maximum, with a width of about 19 m and a height of about 1.2 m, and the water storage capacity increases to its maximum. The height of the water-conducting fracture zone eventually increases to 202 m. [ABSTRACT FROM AUTHOR]

Whether mudstone is rich in or free of organic matter has a great influence on the occurrence of water. Comparing different types of water in organic-rich and organic-free mudstones is helpful for further understanding the role of water in hydrocarbon generation. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) combined with mass spectrometry (MS) afford the opportunity to identify the mass change, reactions and products of the sample in a real-time monitored heating process. This study compared the pyrolysis characteristics of an organic-rich mudstone (CN1) and an organic-free mudstone (CW1) by using the TGA/DTA-MS method to estimate the content of different types of H2O and CO2 in organic-rich mudstones. The results show that the mass changes in CN1 and CW1 can be divided into the three thermogravimetric (TG) stages of 0°C-200°C, 200°C-650°C, and 650°C-900°C, while the peak temperatures of H2O and CO2 obtained through MS are different for CN1 and CW1. The differences in mineral components and organic matter between CN1 and CW1 suggest that the MS peaks of H2O and CO2 in CW1 are mainly influenced by clay and carbonate minerals, and that those of CN1 are also influenced by organic matter. In addition, quantification equations for CO2 and H2O contents from both the organic and inorganic origin of the organic-rich mudstone can be established by using the MS peak area of CO2 and H2O, mass loss in TGA and the mineral composition of the organic-free mudstone. This work provides useful insights for further understanding the hydrocarbon generation mechanism, as well as quantifying different types of water in organic-rich mudstones. [ABSTRACT FROM AUTHOR]

AbstractDuring seasonal rainfall periods, natural rocks typically undergo repeated wetting-drying cycles, which directly affects the micro-structure of the rock samples and consequently leads to the deterioration of their mechanical properties, especially in mudstone. Therefore, this paper investigated the degradation pattern of strength parameters and failure pattern of mudstone samples under wetting-drying cycles through a series of laboratory tests and quantitatively characterized the micro-structural changes in the samples. Additionally, numerical simulations were utilized to delve deeper into the degradation mechanism of the samples. The results indicate that with an increasing number of wetting-drying cycles, the degradation of peak strength and elastic modulus becomes more pronounced. Moreover, there is a continuous increase in micro-porosity within the samples, accompanied by changes in pore structure and morphology. According to the simulation results, the wetting-drying cycles change how the samples fail, transitioning from mixed tensile-shear failure to predominantly shear failure. This study not only deepens the theoretical understanding of the deterioration mechanisms in mudstone but also provides important guidance for practical applications. [ABSTRACT FROM AUTHOR]

Ground subsidence caused by extraction of longwall panels has always been a great concern all over the world. Conventional longwall mining system (CLMS) gives rise to wavy subsidence causing great damage to surface structures. A coal mine in Shanxi, China, utilizes a split-level longwall layout (SLL) for a sub-horizontal No. 8 coal seam to improve the cavability of mudstone interlayer and top coal. This layout, however, also produced unexpectedly favorable surface subsidence. Subsidence of No. 6 and No. 8 longwall panels was monitored while mining was conducted. Field instrumentation and numerical simulation were carried out. It is demonstrated that an asymmetric subsidence profile with stepped subsidence and cracks occurred on the tailgate side but relatively mild and smooth deformation on the other. Due to elimination of conventional parallelepiped gate pillar, No. 6 and No. 8 gobs were connected. Extraction of two SLL panels acted as one supercritical panel. The maximum possible subsidence was reached which lowers the likelihood of potential future secondary subsidence as underground gob fractures and voids have closed. Therefore, SLL is more favorable for post-mining land reuse as gobs are more consolidated underground. [ABSTRACT FROM AUTHOR]

It is the first time that the fossil footprints of a group of Middle Eocene elephant ancestors have been discovered in the Gonjo Basin, East Tibet Plateau. The Gonjo Formation is attributed to the Middle Eocene Epoch (U-Pb age = 44.7 ± 1.2 Ma) and consists mainly of purplish-red, medium- to coarse-grained sandstones, siltstones interbedded with mudstones, and conglomerates with sedimentary structures like ripple marks, rip-up clasts, and trough-cross bedding, suggesting fluvial-lacustrine systems. The group of fossil footprints has a characteristic oval-concave shape, and the toe impressions are absent. Some fossil footprints are overstepped with a pockmarked texture resembling Proboscipeda enigmatica. More than 165 fossil footprints of the group are relatively well-preserved with different diameters, which is evidence of highly social behavior and trackmakers of different ages, including calves, juveniles, adolescents, and adults. The size frequency of the fossil footprints enabled us to deduce the body mass, shoulder height, and hip-height distribution of the trackmakers that crossed the East Tibet Plateau 44.7 Ma ago. The trackmakers comprised an estimated average hip-height of 111.8 cm, an average shoulder height of 172.8 cm for males/155.9 cm for females, and an average body mass of approximately 1 218.1 kg for males/907.8 kg for females. The abundance of fossil footprints reveals that in the Middle Eocene Epoch, the environment was extraordinarily conducive for the elephant ancestors to live in the East Tibet region. [ABSTRACT FROM AUTHOR]

Understanding the deformation and damage behaviors of soft rocks under temperatures and water–rock interactions is crucial for designing rock engineering structures and for assessing geotechnical disasters. Hence, the physical–mechanical characteristics and damage mechanisms of silty mudstone under heating and water-cooling cycles were determined by a series of laboratory tests. The results indicate that heating and water-cooling treatments prompt crack development within silty mudstone, observable through volume augmentation along with reductions in mass, density, and P-wave velocity. The interconnections between the decrease of mechanical properties such as elastic modulus, cohesion, and internal friction angle of silty mudstone and the factors including temperatures and cycle number are explicitly established. The deterioration of the physical–mechanical properties of silty mudstone primarily arises from the thermal expansion, dehydration, and hydrolysis of mineral constituents. Furthermore, a new damage constitutive model for silty mudstone considering temperature and the number of heating and water-cooling cycles is established based on lognormal distribution and the Mohr–Coulomb criterion. Additionally, the model parameters S0 and F0 characterize the homogeneity and average strength, enabling a quantitative assessment of the damage degree of rocks. [ABSTRACT FROM AUTHOR]

The DP-coloring is a generalization of the list coloring, introduced by Dvořák and Postle. Let H = (L , H) be a cover of a graph G and P DP (G , H) be the number of H -colorings of G. The DP color function P DP (G , m) of G, introduced by Kaul and Mudrock, is the minimum value of P DP (G , H) where the minimum is taken over all possible m-fold covers H of G. For the family of n-vertex connected graphs, one can deduce that trees maximize the DP color function, from two results of Kaul and Mudrock. In this paper we obtain tight upper bounds for the DP color function of n-vertex 2-connected graphs. Another concern in this paper is the canonical labeling in a cover. It is well known that if an m-fold cover H of a graph G has a canonical labeling, then P DP (G , H) = P (G , m) in which P(G, m) is the chromatic polynomial of G. However the converse statement of this conclusion is not always true. We give examples that for some m and G, there exists an m-fold cover H of G such that P DP (G , H) = P (G , m) , but H has no canonical labelings. We also prove that when G is a unicyclic graph or a theta graph, for each m ≥ 3 , if P DP (G , H) = P (G , m) , then H has a canonical labeling. [ABSTRACT FROM AUTHOR]

Understanding the cracking behaviors and failure mechanisms of soft rocks with existing cracks is crucial in designing rock engineering structures. Hence, we studied the influence of crack parameters, including crack inclination angle, crack number, and crack form, on the strength characteristics and cracking behaviors of silty mudstone using uniaxial compression tests and numerical simulation. The mechanisms of crack initiation, propagation, and coalescence in silty mudstone with preexisting cracks are discussed in this paper. The results showed that the stress-strain curves of silty mudstone with preexisting cracks can be divided into three stages: the load compaction, crack extension, and postpeak damage stages. Preexisting cracks had a weakening effect on the mechanical properties of silty mudstone, and the main order of influence of the various factors was crack inclination angle, crack number, and crack form. The failure mode of silty mudstone with preexisting vertical cracks was mainly composite tensile-shear failure; the failure modes of rocks with single and double cracks were tensile failure, shear failure, and composite tensile-shear failure. The damage process of silty mudstone with preexisting cracks under stress was as follows. The propagation and coalescence of cracks caused cracking of weak surfaces within the rock mass. The cracks propagated along the axial stress direction or preexisting crack direction under different stress states to form macroscopic crack surfaces, which ultimately led to rock mass failure. In addition, the strength characteristics and cracking behaviors of silty mudstone simulated using FLAC3D version 6.0 were consistent with the experimental results. [ABSTRACT FROM AUTHOR]

Due to limited data on the geochemical properties of natural gas, estimations are needed for the effective gas source rock in evaluating gas potential. However, the pronounced heterogeneity of mudstones in lacustrine successions complicates the prediction of the presence and geochemical characteristics of gas source rocks. In this paper, the Liaohe Subbasin of Northeast China is used as an example to construct a practical methodology for locating effective gas source rocks in typical lacustrine basins. Three types of gas source rocks, microbial, oil-type, and coal-type, were distinguished according to the different genetic types of their natural gas. A practical three-dimensional geological model was developed, refined, and applied to determine the spatial distribution of the mudstones in the Western Depression of the Liaohe Subbasin and to describe the geochemical characteristics (the abundance, type, and maturation levels of the organic matter). Application of the model in the subbasin indicates that the sedimentary facies have led to heterogeneity in the mudstones, particularly with respect to organic matter types. The effective gas source rock model constructed for the Western Depression shows that the upper sequence (SQ2) of the Fourth member (Mbr 4) of the Eocene Shahejie Formation (Fm) and the lower and middle sequences (SQ3 and SQ4) of the Third member (Mbr 3) form the principal gas-generating interval. The total volume of effective gas source rocks is estimated to be 586 km³. The effective microbial, oil-type, and coal-type gas source rocks are primarily found in the shallow western slope, the central sags, and the eastern slope of the Western Depression, respectively. This study provides a practical approach for more accurately identifying the occurrence and geochemical characteristics of effective natural gas source rocks, enabling a precise quantitative estimation of natural gas reserves. [ABSTRACT FROM AUTHOR]

The first of two communications is devoted to the study of lithogeochemical features of the pilot collection of Upper Precambrian sandstone and siltstone samples taken from four boreholes: Bogushevskaya 1, Bykhovskaya, Lepel 1, and Kormyanskaya (Belarus). This article analyzes the general features of their bulk chemical composition and shows the possibilities and limitations for further reconstructions. It has been established that Riphean and Vendian rocks included in the pilot collection, visually identified as sandstones, are actually quartz, feldspar–quartz, and arkosic varieties with different cement types. In terms of geochemical characteristics, the Vendian "siltstones" correspond to the coarse- and fine-grained siltstones and, to a greater extent, mudstones with a predominance of illite, as well as various admixtures of berthierine, kaolinite, and smectite. Based on the comparison of enrichment factor (EF) of the trace element, these rocks are marked by several dissimilarities related to both variations in the source rock composition and sedimentary environment. Data points of the samples on the Zr/Sc–Th/Sc diagram indicate that all of the studied Riphean and Vendian rocks are dominated by the first sedimentation cycle material, suggesting that the lithogeochemical characteristics of the pilot collection rocks quite correctly reflect similar features of the source rock complexes. Therefore, they can be used to reconstruct the paleogeodynamic and paleoclimatic factors that controlled the accumulation of Riphean and Vendian sedimentary sequences in Belarus. [ABSTRACT FROM AUTHOR]

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