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In this research, a 3D multiscale model was applied for the analysis of long-term deformation of mudstone under high stress. Firstly, Voronoi tessellation generating and cohesive elements inserting programs were developed by Python-driven ABAQUS to establish a multiscale numerical analysis platform. In addition, creep damage effects for high stress were investigated through tests. Extended Drucker–Pranger model with strain hardening creep was developed for the calculation of mudstone viscoelastic plasticity. Finally, the creep damage model was integrated with multiscale analysis platform to evaluate the creep process of samples. The results verified that the developed model was effective in multiscale numerical analysis. [ABSTRACT FROM AUTHOR]

The purpose of the present study is to investigate the initial irreversible critical damage state of red mudstone during the elastic stage of the stress–stain curve. First, a series of uniaxial and triaxial compression tests were carried out using a digital image correlation (DIC) based high spatial and temporal resolution 3D visualization test system of multi-field coupling damage of rocks. The time-dependent strain on the surface of rock samples during the test process was captured by DIC technology. The initial irreversible critical damage state of red mudstone was then investigated by analyzing damage process in macroscopic and mesoscopic scales in an integrated manner through developing theoretical models based on critical deceleration theory. It demonstrates that the developed models can recognize the initial irreversible critical damage point of the rocks by analyzing the DIC-measured deformation behavior of the samples in both macroscopic and mesoscopic level. Highlights: Studied the variance increase characteristics of mesoscopic strain at the crack site of red mudstone during the elastic stage Proposed the initial irreversible critical damage state of red mudstone under the influence of strength and confining pressure Study results enrich the theory of rock mechanics and can be applied to tunnel design or slope stability investigation, etc. [ABSTRACT FROM AUTHOR]

This study investigated borehole breakout and spalling phenomena through true-triaxial experiments conducted on cubic Gosford sandstone and yellow mudstone specimens. The experiments were carried out based on the custom-developed borehole breakout testing system, which could enable the pre-stressed (PS) tests (applying stresses onto intact specimens and then drilling). In comparison to the pre-drilled (PD) tests (applying stresses onto specimens with pre-drilled boreholes), the PS tests consistently resulted in wider and deeper breakouts under the same far-field stresses in both rock types, which are attributed to the impacts of excavation-unloading and removal of rock debris. The results from 36 PS tests indicated that the breakout and spalling extent are affected by all three principal stresses, and the impact of each stress was also quantitively assessed and compared. Moreover, analysis of experimental data from this study and the literature revealed that a unique correlation between breakout angle and normalised breakout depth could not be obtained, suggesting deriving two principal stress components from two breakout geometries should be viable. Furthermore, empirical correlations based on the maximum tangential stress (σmax) and out-of-plane stress were developed to characterise the breakout geometries, which outperformed those previous relations based solely on σmax across all datasets. This suggests that while the breakout and spalling phenomena are primarily controlled by σmax, a more accurate representation of failure extent can be achieved by considering the out-of-plane stress. Highlights: Borehole breakout experiments were conducted on sandstone and mudstone through a custom-designed true-triaxial testing system. The impacts of testing methodologies and the magnitude of each principal stress on breakout geometries were analysed in both rock types. The correlation between breakout angle and normalised breakout depth was investigated based on six pre-stressed datasets. Empirical equations based on the maximum tangential stress and out-of-plane stress were developed to characterise the breakout geometries. [ABSTRACT FROM AUTHOR]

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]

The propagation characteristics of sea seismic wave (SSSW) in different underwater media are different. This study mainly focuses on the propagation characteristics of SSSW in different underwater media to improve the detection ability of SSSW mines. The propagation of SSSW in different underwater media, including clay, sandy clay, sandstone, mudstone, hard stone, and dolomite, is simulated using the staggered grid finite difference method. The dispersive energy maps of different underwater media are extracted using the f-k dispersive energy extraction method. Compared with the results of Scholte wave dispersion characteristic equations, the simulation results are consistent with the theoretical results. At the same time, the attenuation law of the SSSW train is obtained. The results provide a theoretical basis for developing SSSW mine fuses. [ABSTRACT FROM AUTHOR]

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]

In order to investigate the failure mechanism of the reinforced muddy soft rock under the influence of the hydration reaction when ground water is present, a series of confined compressive tests and Acoustic Emission (AE) recordings were conducted subject to various moisture content levels and lateral confining stresses. It was found that the failure modes of the reinforced rock specimen were affected by the moisture content level and the lateral stress σ2 in a way that the load bearing capacity of the reinforced rock would increase with the lateral stress σ2 but decrease as the moisture content increased. An increase in the moisture content would reduce the extent of the influence of the lateral stress on the load bearing capacity of the reinforced rock. In addition, much less AE counts were recorded when the moisture content increased indicating that the crack initiation and propagation in this case was easier due to the reduction of the required external input energy. With increasing moisture content, the failure mode of the specimen gradually changes from sudden and brittle to progressive and ductile. Moreover, the hydration reaction became more significant leading to a complete debonding between the grout and the rock. Consequently, the reinforcement provided by the rock bolt to the rock became negligible. [ABSTRACT FROM AUTHOR]

Helium reservoirs, as an indispensable and scarce strategic resource, can be categorized into two primary origins: crust- and mantle-sourced. Understanding the mechanisms of its formation and accumulation is a crucial challenge in helium exploration. Previous work on helium exploration has mainly focused on crustal helium, while mantle-sourced helium-rich reservoirs have been overlooked. Helium reservoirs with both a crustal and a mantle source exhibit higher helium abundance than that of crustal helium reservoirs and are sporadically distributed in Neogene basins worldwide, but their formation and evolution is poorly understood. In Eastern China, several Neogene basins preserve high quality crust/mantle helium-rich reservoirs, and in this study, we use the Subei Basin as a case study to investigate processes controlling He accumulation and storage. The helium reservoirs can be classified into two types based on the lithological nature of the structural traps: sand reservoir with mud cap and basalt reservoirs with mud cap. The main controlling factors for the formation of crust–mantle helium-rich reservoirs include deep-seated faults, magmatic activity, and mineralization of mantle-derived CO2. Deep-seated faults, along with their associated strike-slip faults, serve as favourable pathways for mantle-derived helium migration and magma upwelling. Magmatic activities serve as the material source for mantle-derived helium as well as the carrier medium in the migration of mantle-derived volatiles. The presence of well-developed sandstone and basalt reservoirs, along with mudstone cap rocks, and the dissolution and mineralization caused by mantle-derived CO2 are important factors in helium accumulation and preservation. [ABSTRACT FROM AUTHOR]

The timing, tempo, and causative mechanisms of Ocean Anoxic Event 1a (OAE1a), one of several such abrupt perturbations of the Mesozoic global carbon cycle, remain uncertain. Mudstones interbedded with tuffs in Hokkaido, Japan preserve carbon and osmium isotope shifts recording OAE1a. U-Pb zircon ages of tuffs constrain the OAE1a onset to 119.55 +0.072/-0.079 million years ago (Ma) and its duration to 1116 +87/-93 thousand years (kyr). Isotopic excursions of osmium followed by carbon that mark the rapid onset of OAE1a each lasted ~115 kyr. Critically, the occurrence of index fossil Leupoldina cabri in the Hokkaido OAE1a section, which also caps and thus postdate Ontong Java Plateau (OJP) basalts, has a U-Pb zircon age of ~118.7 to 118.4 Ma. Therefore, OJP volcanism remains a probable source of unradiogenic osmium and light carbon and a causative mechanism of OAE1a. [ABSTRACT FROM AUTHOR]

ABSTRACT The Anambra Basin of Nigeria, part of the larger West and Central African Rift System (WCARS) across Africa, contains primarily Cretaceous to Palaeocene shallow to marginal marine and freshwater sedimentary deposits. The organic‐rich deposits of the Cretaceous Nkporo and Mamu formations within the Anambra Basin and the Palaeocene Imo Formation of the Niger Delta Basin constitute important conventional source rocks. Despite its economic significance, research on organic matter characterisation, palynofacies, sea‐level fluctuations, palaeoclimate, hydrogeography, basin restriction, palaeobathymetry and the factors controlling organic matter preservation remains largely undocumented. The here presented new inorganic and organic geochemical and organic petrography data of the Cretaceous to Palaeocene deposits serve to refine the regional interpretation at a basinal scale and within the supra‐regional context of the WCARS. Geochemical palaeotemperature proxies suggest a warm and humid tropical palaeoclimate during the Late Cretaceous within the study area. Furthermore, the measured TOC values indicate poor to very good organic content. Palynofacies analysis revealed high abundances of opaque and translucent phytoclasts and low amounts of palynomorphs with negligible amorphous organic matter (AOM) in the studied mudrocks. Two palynofacies groups suggest shallow‐marine conditions in a proximal shelf setting and a heterolithic oxic basin. The palynofacies of the upper Imo Formation reveal higher percentages of dinoflagellate cysts during the early highstand phase, with equidimensional, opaque phytoclasts representing the maximum flooding phase, accompanied by warmer conditions. Additionally, abundant terrestrial phytoclasts, Deltoidospora spp., Classopollis spp. and geochemical indicators collectively indicate warm tropical climatic conditions consistent with geochemical interpretations. The palaeobathymetry reconstructions suggest a shallow seaway during the Upper Cretaceous in the Anambra Basin. [ABSTRACT FROM AUTHOR]

Background: At approximately 4:00 PM on 18 July 2023, a heavy rainstorm lasting one hour triggered a significant mudstone landslide in Dongping, Weiyuan County, Gansu Province, Northwest China. The landslide resulted in the burial of houses, the fracturing and destruction of roads, and posed a serious threat to 16 households. The estimated economical loss from this disaster reached 3.2 million yuan. This study presents a detailed field investigation of the Dongping landslide, focusing on the deformation and failure characteristics through a multi-layered analysis of sliding strata, rock mass structure, slope configuration, and failure mechanism. Moreover, the study explores the key triggering factors of the Dongping landslide, with particular attention to the roles of seismic activity, rainfall, and preferential flow in the development of large-scale mudstone landslides. Results: The stratigraphic profile of the Dongping landslide reveals a two-layer structure, consisting of overlying loess and underlying mudstone, with the sliding surface primarily located within the underlying Neogene red mudstone. The initiation location of the Dongping landslide is situated at the rear of the slope, while the main slip-resistant section is located in the middle section of the landslide, exhibiting a predominantly thrust-sliding. After encountering resistance in the middle section, the front part of the sliding mass continued to move, leading to the formation of secondary landslides. The overall movement of the Dongping landslide is characterized by rotational sliding, with the sliding mass remaining relatively intact. Conclusions: The initiation of the large-scale mudstone landslide in Dongping was driven by multiple factors. The heavy rainfall served as the direct triggering factor for the landslide occurrence. However, some historical factors, including seismic activity and previous sliding surface, had already weakened the slope structure by degrading the mechanical properties of the landslide mass and creating preferential flow channels, thereby setting the stage for the Dongping landslide. Structural fractures in the landslide area, along with sinkholes formed by a combination of tectonic joints, soil properties, and human activities, constituted preferential seepage pathways for water within the slope. These pathways provided the hydraulic conditions necessary for rainfall-induced landslides, making them the primary controlling factors in the occurrence of the Dongping landslide. [ABSTRACT FROM AUTHOR]

ABSTRACT As the exploration of deep‐seated oil and gas resources in the Turpan‐Hami Basin intensifies, there is an urgent need to thoroughly depict the geological characteristics of newly uncovered, underexplored strata in sub‐sag centers. This study undertakes the inaugural systematic geochemical analysis of mudstones atop the Sangonghe Formation, including palynological identification, maceral identification, biomarker analysis, total organic carbon (TOC) analysis, and pyrolysis. The findings reveal that the mudstone sequence, as the target layer, was deposited in a warm and moist paleoclimate and a weakly reducing to weakly oxidising saline water environment, fostering the growth of prolific algae and bacteria, thus ensuring substantial foundational materials for source rock formation. The organic matter in the mudstone sequence displays pronounced laminar accumulation. Despite the overall modest abundance, the organic matter features notable hydrocarbon‐generating potential per unit of organic carbon and favourable types. Humic‐sapropelic kerogens (type II1) are found in the mudstones, with organic matter generally reaching a mature to highly mature stage. These characteristics establish the mudstones as effective source rocks, furthermore, the hydrocarbon expulsion in the Xishanyao Formation precedes that of the Sangonghe Formation and that both formations constitute a sequential process in terms of hydrocarbon generation and expulsion timing and hydrocarbon contribution. Reanalyzing this mudstone sequence not only revises prior geological understanding of it as direct cap rocks, but also facilitates the reclassification of deep‐seated strata into three distinct petroleum systems. Centered around this source rock layer, dual modes, namely the “lower‐source rock and upper‐reservoir” and the “ lower‐reservoir and upper‐source rock” modes can be formed. These new insights will offer profound implications for hydrocarbon resource evaluation and future hydrocarbon exploration endeavours in the Shuixigou Group within the Taibei sag. [ABSTRACT FROM AUTHOR]

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]

The depositional environment and palaeoecological conditions of a Miocene delta in the Paratethys Basin have been reconstructed based on an integrated sedimentological, ichnological and taphonomic analysis of shell concentrations. Four facies associations, i.e. delta plain, distributary channel, delta front and prodelta, are recognised. The shell concentrations, which are a characteristic feature of the Miocene successions, display different taphonomic signatures in the various parts of the delta system. Delta plain shell concentrations are characterised by unabraded shells with abundant micro-borings and thick micrite envelops formed during colonisation windows and optimum ecological conditions such as good illumination, high nutrient availability and low sedimentation rate. Distributary channel shell concentrations consist mainly of highly abraded, highly fragmented, disarticulated shells that point to long-term high-energy hydrodynamic conditions during their formation. Sporadic shell concentrations in the delta front are composed of chaotic and highly fragmented skeletal elements and co-occur with predominantly suspension-feeding trace fossils such as Arenicolites, Diplocraterion and Skolithos. They reflect a high sedimentation rate and suspension organic particles in a high-energy depositional setting. Prodelta shell concentrations are characterised by moderately fragmented, parallel-oriented shells, preserved within thin-bedded sandstones, intercalated between thick mudstone packages. These concentrations were produced by storm-induced, offshore-directed high-density currents. [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]

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. [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]

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]

Stratigraphic positions and the nature of some breccias and mudstones observed in the Lower Cretaceous McMurray Formation type section (Alberta, Canada) challenge the existing fluvial point bar facies models. The currently applied large‐scale, tidally influenced, sandy bedload facies model suggests that point bars fine upward, where breccias and cross‐strata occur at the base of the succession and mud content increases upward. Instead, this study documents that: (i) mudstone clast breccias are not exclusively associated with basal channel‐lag deposits and can occur throughout the point bar; and (ii) stratified mudstones are not limited to the top of the fining‐upward succession and can occur at or near the channel base. This outcrop data, including lithology, sedimentary structures, trace fossils, bed thickness and boundaries, and the nature of stratal packages, further suggests dynamic interplay between fluvial and tidal processes. This article discusses the potential role of high‐magnitude river floods in temporarily elevated suspended sediment concentrations and highlights that fluid mud processes played a crucial role in mud deposition in both tide‐influenced and fluvial parts of the system. Fluid mud processes allowed mud deposition along the channel base and across the point bar accretion surfaces. The breccias predominantly consist of broken pieces of inclined heterolithic strata and mostly occur on accretion sets of point bars, suggesting erosion and collapse of the point bar rather than of the cutbank. This work introduces a novel perspective to the existing models of point bar sedimentation, offering a new end member and concepts for the interpretation of subsurface data. The authors hope that this research encourages further investigations into similar phenomena elsewhere in the world. [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]

Copyright of Transportation Science & Technolgy is the property of Transportation Science & Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Natural Gas Geoscience is the property of Natural Gas Geoscience and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Abstract In order to investigate the failure mechanism of the reinforced muddy soft rock under the influence of the hydration reaction when ground water is present, a series of confined compressive tests and Acoustic Emission (AE) recordings were conducted subject to various moisture content levels and lateral confining stresses. It was found that the failure modes of the reinforced rock specimen were affected by the moisture content level and the lateral stress σ 2 in a way that the load bearing capacity of the reinforced rock would increase with the lateral stress σ 2 but decrease as the moisture content increased. An increase in the moisture content would reduce the extent of the influence of the lateral stress on the load bearing capacity of the reinforced rock. In addition, much less AE counts were recorded when the moisture content increased indicating that the crack initiation and propagation in this case was easier due to the reduction of the required external input energy. With increasing moisture content, the failure mode of the specimen gradually changes from sudden and brittle to progressive and ductile. Moreover, the hydration reaction became more significant leading to a complete debonding between the grout and the rock. Consequently, the reinforcement provided by the rock bolt to the rock became negligible.

Abstract In order to prevent leakage of pyrolysed oil and gas and the release of contaminants from the top and bottom strata, it is essential to carry out a comprehensive study of the seepage behaviour of these strata under high temperature triaxial stress conditions. The findings of this study will contribute to the development of effective strategies for the containment and integrity monitoring of subsurface reservoirs and storage environments. Mudstone, serving as both the upper and lower strata, offers an effective barrier due to its inherently low permeability. In order to explore the change rule of mudstone sealing performance under high temperature triaxial stress, an air-heated low permeability rock mass air permeability measurement system is used to measure the ground stress buried 500 m deep and the temperature variation characteristics of mudstone permeability on the roof and floor of Jimsar oil shale in Xinjiang under 100 °C. It was found that the permeability of stressed mudstone decreased with the temperature rising up to 100 °C. The primary factor influencing the outcome was the thermal expansion of the mudstone. The magnitude of the drop value was contingent upon the triaxial stresses that could potentially be induced by the application of significant tensile forces, resulting in a relatively minor drop value. The average hydraulic radius of pore in the mudstone was also calculated, which also exhibited continuous reduction as heating up to 100 °C and the degree of reduction could reach 68%. The capacity, that prevent oil & gas and contaminant from moving cross strata as a barrier, would be strengthened when the mudstone strata from roof and floor experienced the temperature low than 100 °C. The barrier performance of mudstone as a pollutant migration barrier layer to gas pollutant migration during in-situ heat injection mining of oil shale was further evaluated.

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.

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.

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]

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]

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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]