Core Hole Research Articles

Study on SiO2 Nanofluid Alternating CO2 Enhanced Oil Recovery in Low-Permeability Sandstone Reservoirs

Study on SiO2 Nanofluid Alternating CO2 Enhanced Oil Recovery in Low-Permeability Sandstone Reservoirs

Multiple-core-hole resonance spectroscopy with ultraintense X-ray pulses

Understanding the interaction of intense, femtosecond X-ray pulses with heavy atoms is crucial for gaining insights into the structure and dynamics of matter. One key aspect of nonlinear light–matter interaction was, so far, not studied systematically at free-electron lasers—its dependence on the photon energy. Here, we use resonant ion spectroscopy to map out the transient electronic structures occurring during the complex charge-up pathways of xenon. Massively hollow atoms featuring up to six simultaneous core holes determine the spectra at specific photon energies and charge states. We also illustrate how different X-ray pulse parameters, which are usually intertwined, can be partially disentangled. The extraction of resonance spectra is facilitated by the possibility of working with a constant number of photons per X-ray pulse at all photon energies and the fact that the ion yields become independent of the peak fluence beyond a saturation point. Our study lays the groundwork for spectroscopic investigations of transient atomic species in exotic, multiple-core-hole states that have not been explored previously.

Resonant Auger spectromicroscopy in ultrathin Fe films on W(110)

L3MM Auger transition is measured near the L3 resonance of ferromagnetic Fe films on W(110). The kinetic energies of the Auger peaks display the typical Raman behaviour for photon energies well below the absorption threshold, where the Auger energy follows the changes in the photon energy. Classical Auger behaviour with constant kinetic energy sets in at about 1.5 eV below the L3 resonance independently from the number of Fe layers down to the monolayer thickness. Strong x-ray circular magnetic dichroism is observed at the L3 edge in the entire L3MM Auger spectrum. Different Auger features originating from the final state with two 3p core holes show slight variations in the dichroic signal, which is attributed to the exchange interaction between the core holes and the valence band. Finally, XMCD-PEEM magnetic domain imaging using Auger electrons is demonstrated with a high level of contrast and lateral resolution approaching that of imaging with secondary photoelectrons.

The development of cataclastic bands in high-porosity sandstones: Insights from ring shear experiments

Investigating the deformation mechanism of cataclastic bands in high-porosity sandstone is crucial for understanding the juxtaposition sealing ability of sandstones in a bed sequence. However, deformation bands that are developed in the field and rock cores do not reflect the evolutionary history of the host rock; therefore, the continuous deformation of high-porosity sandstone cataclastic bands cannot be observed. This paper analyzes the deformation mechanism that affects a cataclastic band when high-porosity sandstone faults form. Based on the latest independently developed high-pressure/low-speed ring shear experimental apparatus, the formation and evolutionary process of cataclastic bands in high-porosity sandstone were studied through the similarities among artificial cores. During the experiments, the effective normal stresses and fault displacement were used as single variables. After the experiments, plunger samples were drilled in the lateral direction, and thin sections were prepared to observe and analyze the thickness and particle characteristics of the deformation bands, thereby characterizing the deformation process of the damage zone. The experimental results reveal that high-porosity sandstone undergoes different intensities of cataclasis during the shearing process, and the evolutionary characteristics can be divided into four primary stages. The particles in the sandstone are successively subjected to rotation, rolling, cracking, cataclasis, and other changes after forced deformation. In terms of the macrostructure, a deformation band can be divided into two layers: an inner zone and an outer zone. From the host rock and the outer zone to the inner zone, the orientational arrangement of the particles along the shear direction becomes increasingly clear, and a greater displacement indicates a stronger orientational arrangement effect of the particles. In terms of the microstructures, the particle sizes in the deformation band are 2–3 orders of magnitude smaller than those in the host rock and exhibit greater roundness. With increasing shear displacement, the thickness of the cataclastic band first increases and then remains constant. With increasing effective normal stress, the thickness first decreases slightly, then increases and finally decreases slightly. Therefore, stress and displacement are important factors controlling cataclasis. The influence of displacement on cataclasis is clear at the initial stage, and stress determines the maximum intensity of cataclasis. Additionally, the increase in displacement will be favorable for roundness when the host rock is poorly sorted. These experimental results provide a theoretical basis for future studies on the effects of cataclastic bands and fluid flow.

Determination of the in situ hydraulic parameters of the Callovo–Oxfordian clay rock in a long-term hydraulic interference testing at Andra's Underground Research Laboratory (CMHM)

Abstract. Between 2009 and 2015, Andra has conducted a unique long-term hydraulic interference test in two parallel boreholes 1 m apart from each other and air core drilled in the undisturbed Oxfordian Clay rock at Andra's Underground Research Laboratory (CMHM) in Bure, France. The experimental set-up consisted of six test intervals positioned along the parallel boreholes drilled from a drift located within the Callovo–Oxfordian clay at around 500 m b.g.l. (below ground level). The 20 m boreholes were oriented around 30∘ downwards. The pressure sensors linked to six intervals of 1 m length each allowed for continuous pressure measurement over 6 years and a slanted borehole for the observation of rock displacements (see Fig. 1). Additionally, flow rates were measured during water injection tests that lasted weeks or months. This extensive set of hydraulic data allowed, for the first time, a precise determination of the in situ Callovo–Oxfordian clay rock permeability and anisotropy and its specific storage at the metre to decametre scale. It was achieved based on an automated calibration, using a 3D flow model and explicitly considering all the relevant hydraulic elements acting on the flow system (such as rock mass, borehole disturbed zone and sealing elements) and the drift acting as a steady sink due to the underground ventilation (see Fig. 2). The history matching was performed on the transient pressure measurements. The obtained numerical calibration results were in close agreement with the hydraulic parameter values of the Callovo–Oxfordian clay determined at a smaller scale (single borehole tests and rock core samples in the laboratory), therefore demonstrating the reliability of the very low permeability of the Callovo–Oxfordian clay at the metre to decametre scale. Furthermore, the modelling illustrated the impact of the measurement set-up and its details on the observed hydraulic behaviour. The analysis methodology and the main findings will be presented.

DFT + U Simulation of the X-ray Absorption Near-Edge Structure of Bulk UO2 and PuO2.

Hubbard U-corrected density functional theory within the periodic boundary condition model in the WIEN2k code is used to simulate the actinide LIII and O K edge X-ray absorption near-edge structure (XANES) for UO2 and PuO2. Spin-orbit coupling effects are included, as are possible excitonic effects using supercells with a core hole on one of the atoms. Our calculations yield spectra in excellent agreement with previous experiments and superior to previous simulations. Density of states analysis reveals the mechanism behind the XANES peaks: the main contribution to the U/Pu LIII edges comes from the U/Pu d states hybridized with O p states, while as expected, the O p states primarily determine the O K edges of both UO2 and PuO2. The O K edges also feature O p hybridizing with U/Pu d and f states in the low-energy region and with U/Pu s and p states for the higher-energy peaks.

Evaluation of rock mass units using a non-invasive geophysical approach

Thorough and accurate assessment of rock mass units is important for development of engineering infrastructures and groundwater resources assessments. Rock mass units are widely evaluated by reliable geomechanical parameters namely rock quality designation (RQD) and rock core index (RCI). Conventionally, these parameters are acquired via an extensive number of geotechnical tests. Such tests, however, suffer efficiency for data coverage, cost, equipment and topographic constrictions, and hence cause ambiguity in geological models for a detailed evaluation of rock mass integrity. Conversely, geophysical surveys offer fast, more user-friendly, less invasive, more cost-effective and less time-consuming approach for geological investigations. The past research confirms a useful link between geophysical and geotechnical parameters. But, none of the past studies provides a suitable and generalized relation between these parameters which can reduce geotechnical model uncertainty mostly caused by inadequate data and subsurface heterogeneity. This paper proposes a meaningful and feasible method to obtain geomechanical parameters using a certain number of drillings and geophysical data of four different sites. Based on electrical resistivity obtained from electrical resistivity tomography (ERT) and controlled-source audio-frequency magneto telluric (CSAMT), this research provides the general and adaptable formulas for geotechnical parameter estimation and reduces geological model uncertainty for more detailed 2D/3D imaging of RQD and RCI covering the whole sites where even no drilling data exists. Thus, the investigated sites are assessed laterally and vertically along each geophysical profile via distinct value ranges of geological parameters for a thorough and reliable evaluation of rock mass units in highly heterogeneous setting. Our research reduces the ambiguity caused by structural heterogeneities and scarce data, fills the gap between inadequate well tests and the true geological models, and gives new insights into the rock mass units for proper engineering design and groundwater exploitation.

A DEM parameters calibration method for three-dimensional model of the lunar rock based on the approximate model

The development of an accurate rock discrete element model is essential for modeling core drilling in the lunar environment. However, most of the microscopic parameters of the discrete element model cannot be determined directly by tests. Consequently, a rapid calibration method for microscopic parameters was developed, combining an approximation model, multiple objectives with particle swarm optimization algorithm (MOPSO), and orthogonal experimental design (OED). Range analysis and variance analysis were conducted to investigate the sensitivity of these parameters. Through this approach, the optimal solution for microscopic parameters was obtained to align with the mechanical characteristics of lunar rock simulant, providing a foundation for rock core drilling. The results demonstrate a high level of agreement between the simulated stress-strain curves and the test results. The deviation between the mechanical strength parameters and actual test values was found to be less than 5%, confirming the effectiveness and rationality of the proposed parameter calibration method. This method holds significant potential for widespread application in calibrating the parameters of discrete element models for rock materials.

Hybrid self-centering dual rocking core system for seismic resilience by controlling both structural and nonstructural damage

This study proposes a novel hybrid self-centering dual rocking core (HSDRC) system with structural and nonstructural damage control functions for the building structure’s seismic resilience. The rigid rocking cores (RCs), viscous dampers (VDs), and shear friction spring dampers (SFDs) are introduced in HSDRC systems. The rocking cores with pinned bases are adopted for promoting uniform inter-story drifts over the building height. The SFDs are introduced to dissipate hysteretic energy and bring self-centering capacity by eliminating residual deformation. The VD’s velocity-proportional damping can help HSDRC systems control the nonstructural damage and building content’s damage sensitive to absolute floor accelerations. The expected behavior of HSDRC systems is first described. A direct displacement-based design (DDBD) method is following proposed to achieve the desired nonlinear behavior of HSDRC. Following the developed DDBD procedure, six HSDRC systems are designed. For highlighting the advantages of HSDRC systems compared to the existing self-centering energy-absorbing rocking core (SEDRC) system, two SEDRC systems are also designed. Nonlinear dynamics were included for investigating the performance of the designed systems subjected to seismic events. The numerical results demonstrate that the designed HSDRC systems show the expected nonlinear behavior and achieve the design target, confirming the developed DDBD method’s effectiveness. Compared to SEDRC systems, the newly proposed HSDRC systems show smaller absolute floor acceleration responses while obtaining the comparative capacity in controlling both peak and residual inters-tory drifts, indicating the proposed HSDRC systems can be a promising seismic resilient structural system for both structural and nonstructural damage control.

Persistent Homology as a Heterogeneity Metric for Predicting Pore Size Change in Dissolving Carbonates

AbstractAccurate prediction of physical alterations in carbonate reservoirs under dissolution is critical for development of subsurface energy technologies. The impact of mineral dissolution on flow characteristics depends on the connectivity and tortuosity of the pore network. Persistent homology is a tool from algebraic topology that describes the size and connectivity of topological features. When applied to 3D X‐ray computed tomography (XCT) imagery of rock cores, it provides a novel metric of pore network heterogeneity. Prior works have demonstrated the efficacy of persistent homology in predicting flow properties in numerical simulations of flow through porous media. Its ability to combine size, spatial distribution, and connectivity information make it a promising tool for understanding reactive transport in complex pore networks, yet limited work has been done to apply persistence analysis to experimental studies on natural rocks. In this study, three limestone cores were imaged by XCT before and after acid‐driven dissolution flow‐through experiments. Each XCT scan was analyzed using persistent homology. In all three rocks, permeability increase was driven by the growth of large, connected pore bodies. The two most homogenous samples saw an increased effect nearer to the flow inlet, suggesting emerging preferential flow paths as the reaction front progresses. The most heterogeneous sample showed an increase in along‐core homogeneity during reaction. Variability of persistence showed moderate positive correlation with pore body size increase. Persistence heterogeneity analysis could be used to anticipate where greatest pore size evolution may occur in a reservoir targeted for subsurface development, improving confidence in project viability.

Experimental Investigation of Stress Sensitivity of Elastic Wave Velocities for Anisotropic Shale in Wufeng–Longmaxi Formation

The shale of the Wufeng–Longmaxi formation in the Sichuan Basin is the preferred layer for shale gas exploration in China, and its petrophysical characteristics are the key to geological and engineering sweet spot prediction. However, the characteristics and impact mechanisms of its acoustic wave velocity and elastic anisotropy are currently unclear. In this paper, the Wufeng–Longmaxi shale is taken as the research object, and the P-wave and S-wave velocities of the samples are tested under the loading and unloading processes of confining pressure. The stress sensitivity variations in parameters such as wave velocity, wave velocity ratio, and anisotropy are discussed. P-wave and S-wave anisotropy parameters are correlated under different pressure conditions. X-ray diffraction, casting thin sections, scanning electron microscopy, micron CT scanning, and other analytical techniques are used to explore the mechanisms of stress sensitivity of elastic parameters. The research results indicate that: (1) the acoustic velocities of samples from different angles are V90° > V45° > V0°, and there is a positive correlation between the wave velocity and the confining pressure. After unloading the confining pressure, irreversible plastic deformation occurs due to the closure of some microfractures in the rock core, causing the wave velocity to be higher than the initial value. (2) The stress sensitivity coefficient of the P-wave (The mean is 3.00 m·s−1·MPa−1) is higher than that of the S-wave (the mean is 1.23 m·s−1·MPa−1), and the stress sensitivity coefficient of the compacted stage (the mean is 3.02 m·s−1·MPa−1) is higher than that of the elastic stage (the mean is 1.21 m·s−1·MPa−1). (3) The anisotropy of the P-wave and S-wave is negatively correlated with the confining pressure. When the confining pressure is loaded to 65 MPa, the change rate of the P-wave anisotropy coefficient is 23%, and its stress sensitivity is higher than that of S-wave anisotropy coefficient (the change rate is 13.7%). After unloading the confining pressure, the degree of anisotropy is reduced due to the closure of some microfractures. The empirical formula of P-wave and S-wave anisotropy parameters under different pressures is established through linear regression, which can provide a reference for mutual predictions. (4) The variation in wave velocity anisotropy with stress can be divided into stress and material anisotropy, which are related to the directional arrangement of microfractures and clay minerals, respectively. The quantitative characterization of shale anisotropy can be realized by evaluating the development degree of reservoir fractures and mineral components, providing a reference for logging interpretations, sweet spot prediction, and fracturing construction of shale gas reservoirs.

Weathered bedrock converts hydrological processes in loess hilly-gully critical zone

Weathered bedrock ecohydrology is indispensable for terrestrial ecosystem stability; however, the influence on the hydrological processes is poorly understood in loess hilly-gully critical zone. Using simulation experiments and in-suit observations, this study evaluated the intervention of weathered bedrock particles on profile infiltration and evaporation, investigated rock core sample characteristics and detected the spatiotemporal water variation in hillslopes of woodland and shrubland. Results showed that adding weathered bedrock particles interfered with infiltration and evaporation processes. Infiltration simulation discovered that stable infiltration rates increased linearly with weathered bedrock thicknesses, which accelerated by 0.5–5.7 times more than bulk soil layers. Interestingly, due to water separation at soil-rock interface, there existed nonlinear initial and average infiltration intensity fluctuations. Evaporation simulation demonstrated that cumulative evaporation presented a linear decrease with weathered bedrock, while the initial daily evaporation intensity increased, reaching a maximum of 15.4 ± 2.2 mm d−1. Moreover, borehole investigations manifested that weathered bedrock layers presented a thickness of more than 5.0 m, and the weathering intensity gradually decreased with depth, which was related to terrains and locations in hillslopes. Furthermore, profile water movement monitoring between woodland and shrubland slopes demonstrated that weathered bedrock optimized profile hydrological allocation. The average rock moisture reached about twofold than soil moisture, with average soil and rock moisture of 0.07 ± 0.04 cm3 cm−3 and 0.15 ± 0.05 cm3 cm−3 in woodland, 0.08 ± 0.03 cm3 cm−3 and 0.15 ± 0.03 cm3 cm−3 in shrubland, respectively. Besides, the profile water storage changed dynamically in equilibrium and escalated linearly with weathering layer thickness. Fundamentally, a conceptual structure model covering soil and rock water balance, vegetation dynamics, and climate change was constructed and discussed throughout the Earth’s critical zone, which was then applied in describing water circulation participating by rock moisture under relative water shortage and abundance scenarios in loess hilly-gully regions. This study would furnish insights for improving and deepening the water cycle in shallow soils, and provide new horizons for enriching water resources utilization under climate change.

The Failure Law and Combined Support Technology of Roadways with Weak Surrounding Rock in Deep Wells

In order to effectively address stability control technology issues of soft surrounding rock roadways in deep mines. This study analyses the deformation and failure characteristics of the surrounding rock of a −962 m horizontal track roadway with original support conditions based on a severe deformation case that occurred in a mine. Upon establishing a mechanical model of surrounding rock failure zoning for circular roadways, which is based on the relationship between the stress–strain curve of soft rocks and the secondary stress distribution and strength of surrounding rock, this study explores the influence of rock strength indicators, disturbance degree, and support resistance on the stress distribution of the surrounding rock. The failure or instability mechanism of high-stress soft and weak surrounding rock is revealed on this basis. A multi-stage strengthening combined support technology is proposed, which consists of “high-strength prestressed anchor bolt (cable) supports as the core, deep and shallow hole groutings as the foundation, bottom angle, and floor anchorage grouting reinforcements as the key.” Moreover, numerical simulation and engineering practice optimize and verify the support scheme. The results show that after adopting the multi-stage strengthening combined support technology, the deformation of the surrounding rock of the roadways was only 12.6~14.3% of that under the original supporting parameters, and the deformation rate was still less than 0.2 mm/d even after 40 days. The proposed surrounding rock support method realizes the stability control of the roadway, which also has specific reference significance for similar projects.

(Digital Presentation) Operando x-Ray Emission/Absorption Spectroscopy to Characterize Electronic Structure Changes of Transition Metals in Lithium-Ion Batteries

Demand for high-performance rechargeable batteries has driven the development of novel electrodes with high reversibility and energy density. Tracking the change in electronic and local structure is crucial to investigate and improve the stability and performance of these batteries. Advanced characterization techniques allow the user to monitor electronic and local atomic structure changes to better understand the role and behavior of different elements during cycling of electrode material for rechargeable batteries.X-ray Absorption and Emission Spectroscopy allow us to explore such changes in 3d transition metal elements through the process of generation and quenching of core holes in the sample. Operando measurements enable real-time monitoring of electronic structure changes in electrode materials which enable us to capture phenomena which are only kinetically accessible.In this study, the change in electronic structure of transition metals present in electrode materials is explored as a function of lithium removal through XES Kβ1,3feature along with K-edge XAFS using a lab-scale instrument. The choice of electrodes explored in this study considers the degree of oxidation, structure, and mechanism for ion storage. Change in peak and edge positions of Kβ1,3and K-edge feature is utilized to monitor oxidation/spin changes in electrode materials during charge/discharge. Further the magnetic behavior for ex-situ samples prepared by electrochemical delithiation of LCO in the range of 2-10% delithiation is investigated using Kα and Kβ fluorescence (spin sensitive) followed by K-edge XAFS for Cobalt and Oxygen. Figure 1

Profile control and plugging ability of extracellular polymeric substances (EPS) produced by E. cloacae strain ZL-02 under Ba2+ in reservoir

Microbial Enhanced Oil Recovery (MEOR) is a pivotal technology for enhancing tertiary oil recovery. The production of partly extracellular polymeric substances (EPS) by Enterobacter cloacae exhibits excellent control over mobility and holds promise for applications in heterogeneous reservoir exploration. To investigate the impact of Ba2+ on microbial EPS production, a series of tests were conducted, including EPS production tests, polysaccharide and protein content analyses, Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) measurements, X-ray diffraction (XRD), laser particle size measurements, and transcriptome analysis.The results demonstrated the stimulating effect of Ba2+ on EPS membrane production. Ba2+ stimulation led to increased secretion of proteins (5.82 g/L) and polysaccharides (9.0 g/L). Moreover, the binding of proteins with Ba2+ resulted in an enlargement of the particle size of the EPS membrane and an increase in grain size, reaching a maximum crystallinity of 77.77 %. Transcriptome analysis revealed the up-regulation of 790 genes and down-regulation of 728 genes in response to Ba2+ addition. Enrichment analysis of the up-regulated genes highlighted the significant enrichment of gene ontology number GO: 00160120, which directly influenced microbial EPS membrane production. Furthermore, microscopic displacement and core flooding experiments were conducted to evaluate the plugging ability of microbial-produced EPS membranes. Remarkably, under the influence of Ba2+, microorganisms exhibited significantly enhanced sealing capacity on glass slides etched with rock cores. The results from simulated flow experiments demonstrated a maximum sealing rate of 81.5 % on rock cores, with an RF (Resistance Factor) value of 2.5 and an RRF (Residual Resistance Factor) value of 5.45.This study innovatively explores oil-producing microbial genes, combining simulation experiments and rock core slicing to reveal the microscale mechanism of Ba2+ stimulating microbial EPS secretion for reservoir plugging. It provides theoretical support for the application of MEOR technology in improving oil recovery rates.

Infrared spectroscopy and chemometric modelling of organic carbon measured by Rock-Eval pyrolysis of UK shale rock

Abstract Shale rock core from the Bowland Shale Formation, UK, was analysed in the laboratory using Rock-Eval pyrolysis and Fourier transform infrared spectroscopy (FTIR). These methods are used to characterize the organic constituents of soil and rock. This research is a proof-of-concept study to investigate whether regression models developed using FTIR and Rock-Eval data for the same length of core can be used to estimate selected Rock-Eval parameters. The accuracy of the regression models was assessed using statistical methods, the results of which were used to choose preferred models for each Rock-Eval parameter. The models produced were shown to have an acceptable level of uncertainty for total organic carbon and S1, S2 and S3 outputs, which led us to conclude that these are potentially suitable for estimating unknown down-core Rock-Eval parameter values. Conversely, the model for the temperature of the maximum rate of hydrocarbon generation ( T max ) had higher variability in the cross-validation data above the acceptable level of uncertainty, which could lead to erroneous estimates. Down-core interpolations of selected Rock-Eval parameters could be practically achieved by modelling FTIR data by maintaining standard sample frequencies for Rock-Eval while supplementing with higher frequencies for FTIR and chemometric analysis.

3D-porous-GAN: a high-performance 3D GAN for digital core reconstruction from a single 3D image

The 3D digital rock technology is extensively utilized in analyzing rock physical properties, reservoir modeling, and other related fields. This technology enables the visualization, quantification, and analysis of microstructures in rock cores, leading to precise predictions and optimized designs of reservoir properties. Although the accuracy of 3D digital rock reconstruction algorithms based on physical experiments is high, the associated acquisition costs and reconstruction processes are expensive and complex, respectively. On the other hand, the 3D digital rock random reconstruction method based on 2D slices is advantageous in terms of its low cost and easy implementation, but its reconstruction effect still requires significant improvement. This article draws inspiration from the Concurrent single-image generative adversarial network and proposes an innovative algorithm to reconstruct 3D digital rock by improving the generator, discriminator, and noise vector in the network structure. Compared to traditional numerical reconstruction methods and generative adversarial network algorithms, the method proposed in this paper is shown to achieve good agreement with real samples in terms of Dykstra-Parson coefficient, porosity, two-point correlation function, Minkowski functionals, and visual display.

TECTONOTHERMAL EVOLUTION OF THE ZAGAN METAMORPHIC CORE COMPLEX IN TRANSBAIKALIA AS A RESULT OF THE CRETACEOUS – PALEOCENE MONGOL-OKHOTSK POST-COLLISIONAL OROGEN DESTRUCTION

Thermochronological reconstructions of the Zagan metamorphic core complex were carried out using samples from the central part of the core, mylonite zone detachment and lower nappe with U/Pb zircon dating, 40Ar/39Ar amphibole and mica dating, and apatite fission-track dating. In the tectonothermal evolution of the metamorphic core, there was distinguished an active phase (tectonic denudation) of the dome structure formation during the Early Cretaceous (131–114 Ma), which continued in the Late Cretaceous – Paleocene (111–54 Ma) in passive phase (erosive denudation). During an active phase, there was initiated a large-amplitude gently dipping normal fault (detachment), which was accompanied by tilting (sliding of rocks along subparallel listric faults). As a result, about 7 km thick rock strata underwent denudation over 17 Ma at a rate of about 0.4 mm/year. In passive phase, about 6 km thick rock strata were eroded over 57 Ma, with a denudation rate of about 0.1 mm/year. Thus, the Zagan metamorphic core complex was tectonically exposed from the mid-crust to depths of about 9 km in the Early Cretaceous as a result of post-collisional collapse of the Mongol-Okhotsk orogen. Further cooling of the rocks in the metamorphic core to depths of about 3 km occurred in the Late Cretaceous – Pliocene as a result of destruction of more than 6 km high mountains.

Risk prioritization in a core preparation experiment using fuzzy VIKOR integrated with Shannon entropy method

Accident rates in academic laboratories are increasing rapidly day to day. The incorporation of complex activities with the inclusion of modern technologies and human behavior during experiments often makes it difficult to manage health and safety risks. Failure modes and effect analysis (FMEA) is widely used risk assessment technique that consider (03) risk parameters which include severity (S), occurrence (O), and detection (D), and calculate a risk priority number (R.P.N), which facilitates in failure modes ranking. However, there are some shortcomings associated with this method. This study aims to propose a framework for prioritizing the health and safety risks (failure modes) in an experiment using a widely used Multi-criteria decision-making method, i.e., Fuzzy VIKOR supported by criteria objective weights determined using the Shannon entropy concept. The fuzzy VIKOR method is employed to rank the failure modes based on the maxi group utility and the minimum individual regret. In this study, an experiment related to preparing rock core samples is taken as an example for implementing the proposed technique. Core sample preparation is one of the most common and dangerous experiments in the petroleum industry. The performance of the experiment allows rock sample preparation of desired shape and size to be tested for its hydrocarbon producing potential. The final results indicate that applying the proposed method in a fuzzy environment can efficiently prioritize the experiment’s health and safety risks, which is further considered for the implementation of control measure prioritization. The proposed approach can be applied to other experiments with the same or different domains.

Geochemical Characteristics of Elements and Main Controlling Factors of Organic Matter Enrichment in Shale from Wufeng Formation to Submember Long-11 in Southern Sichuan

A total of 70 shale samples from seven core holes, namely, N203, N208, N209, N210, N211, N215 and N217, in Changning area, south Sichuan, were analyzed for major and trace elements. Based on an analysis of longitudinal variation characteristics of major and trace elements, the REDOX conditions, paleoproductivity, relative sea level height and terrigenous detrital injection amount of gas-bearing shale in Wufeng Formation–Submember Long-11 in the Changning area were studied. And, the main controlling factors of organic matter enrichment in Wufeng Formation–Submember Long-11 were discussed. The results show the following: (1) Trace elements Mo, U, Ba and Ni are relatively enriched in the shale of Wufeng Formation–Submember Long-11 in the Changning area, while the Co element is deficient. The flat distribution pattern of rare earth in Wufeng Formation–Submember Long-11 shows that the shale deposits are weakly influenced by terrigenous materials. The amount of terrigenous injection in Wufeng Formation is higher than that in Submember Long-11, and the amount of terrigenous injection increased gradually from the lower part of Bed Long-111 to the lower part of Bed Long-114. (2) The REDOX environment discrimination indexes such as U/Th, Ni/Co, V/Sc and δU show that the water REDOX conditions of Wufeng Formation–Submember Long-11 in the Changning area have changed many times during the shale sedimentary period, and the overall REDOX conditions are dominated by an anaerobic environment. The REDOX indexes at the boundary between Long-111 and Wufeng Formation are relatively small and in the oxidizing environment range. The REDOX index from Bed Long-111 to Bed Long-114 decreases gradually, and the anaerobic environment of Bed Long-111 and Bed Long-112 gradually changes to the oxygen-poor environment of Bed Long-113; and, the REDOX index of Bed Long-114 is the lowest, which is generally oxygen rich. (3) Organic matter enrichment in Wufeng Formation Submember Long11 in the Changning area is mainly controlled by REDOX conditions. Low terrigenous injection and a relatively high sea level have positive effects on organic matter enrichment, but there is no obvious relationship between the paleoproductivity and organic matter enrichment.