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Understanding the stress-dependent elastic moduli of fractured rocks is essential for monitoring geopressure and tectonic stress. The elastic nonlinearity with finite strains can be described by the theory of acoustoelasticity through the third-order elastic constants (3oECs) that are strictly valid for an isotropic homogeneous medium. The extension to fractured rocks becomes particularly interesting because of the sensitivity of fractures to prestress, but remains largely unaddressed. We address this issue through theoretical modeling with confirmed validity by considering a group of homogeneously distributed fractures (ellipses) embedded into a homogeneous background medium subject to a uniform confining pressure. We incorporate both the David-Zimmerman (DZ) and Mori-Tanaka (MT) models into the theory of acoustoelasticity. The DZ model accounts for the closure influence of cracks with different aspect ratios, whereas the MT model is used to estimate the combining effect of the background acoustoelasticity and the elastic nonlinearity due to the closure of cracks. We validate the acoustoelastic DZ-MT model of fractured rocks by experiment data with Fontainebleau and Vosges sandstones. We show that the effective elastic moduli of fractured rocks mainly depend on the background acoustoelasticity and nonlinear elastic deformations induced by closing cracks. The inclusions inside fractures have too low 3oECs that the associated acoustoelastic effect could be neglected for both interconnected and isolated cracks. The effective elastic moduli of rocks change significantly during the closing period of cracks with increasing pressure under low pressure. The influence of cracks can be reduced only when cracks are closed completely, where, unlike the theoretical prediction by the DZ model, the effective elastic moduli of rocks still increase along with increasing pressure because of the acoustoelastic effect of the background. [ABSTRACT FROM AUTHOR]

Experiments with ten groups of limestone specimens (four samples per group) under ten specific temperatures, 25 °C, 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, 800 °C, and 900 °C, show that the high-temperature effect on the elastic modulus of rocks conforms to thermoelastic responses with a quadratic temperature function. The thermal damage factor can be reduced, by ignoring the effect of Poisson's ratios and densities, to simply a ratio of the P -wave velocities before and after high-temperature treatments. Based on the collected experimental data, we correlate the P -wave velocities change rate with both the peak compressive strength and effective solid matrix. It demonstrates that the high-temperature effect on the thermal damage factor can be directly expressed as the rate of change in the peak compressive strength and effective solid matrix. All these properties (thermal damage factor calculated by the P -wave velocity, peak compressive strength, and effective solid matrix) share a similar exponential trend with increasing temperature. The rates of change in the elastic modulus, P -wave velocity, peak compressive strength, and effective solid matrix also exhibit a similar powerful trend with increasing temperature. This study provides insight into the detailed characteristics of thermal damage related to the mechanical property of limestones exposed to high temperature. [ABSTRACT FROM AUTHOR]

Seismic acquisition geometries have a significant influence on the quality of seismic data in the oil and gas exploration process. Therefore, prior analyses are beneficial to the design of acquisition geometries before implementation of seismic acquisition. The focal beam analysis method can provide quantitative insights into the combined influence of acquisition geometries and subsurface structures. This approach involves a large calculation burden concerning 3D wavefield extrapolation in the case of complex media, thus inhibiting the practical application of focal beam analysis in complex media when using regular CPUs. Therefore, using a graphics processing unit (GPU) to accelerate focal beam analysis becomes imperative. We have developed a fast parallel algorithm to speed up the focal beam analysis for 3D acquisition geometries in complex media on GPUs. Three-dimensional numerical examples show that the GPU-based focal beam analysis runs about 17 times faster than a serial CPU-based one. We also demonstrate the validity and scalability of the proposed approach with numerical examples. The boost in performance afforded by the GPU architecture allows us to analyse 3D acquisition geometries in complex media with less time and at lower cost of hardware. [ABSTRACT FROM AUTHOR]

The wave-induced interlayer flow between mesoscopic-scale heterogeneities (i.e., larger than pore scale but smaller than the predominant wavelengths) is the most important cause of attenuation at frequencies below 1 kHz. According to the White's layered model ( White et al., 1975 ), the wave-induced flow at an interface is symmetrical in periodically layered porous media due to its symmetrical structure. However, in one-dimensional (1-D) randomly layered porous rocks, layers of various thicknesses lead to different types of the interlayer flow. The coexistence of various wave-induced interlayer flow patterns at different interfaces results in interactions. The numerical creep test and a volume average of White's analytical solution were used to analyse the interactions in the two kinds of models (i.e., representative elementary volumes and randomly layered models). One of the parameters used to build a randomly layered model is the standard deviation of the thickness of the water-saturated layer, which could control the interaction strength of the interlayer flow. The detailed characteristics of the interlayer flow interaction were demonstrated by analysing the relative fluid velocity, while the statistical characteristics of the interlayer flow interaction were demonstrated by analysing the average solid velocity. We investigated the effect of the interaction on the amplitude versus the deviation at the interface between a non-dispersive medium and a patchy-saturated dispersive medium in three types of reservoirs. These results are beneficial for describing the distribution of oil/gas patches based on the statistical seismic properties in a layered formation with random disorder. [ABSTRACT FROM AUTHOR]

Correlations between the calculated Coulomb stress changes and observed seismicity rate changes after the Wenchuan earthquake are investigated in this article. Three improvements are made in the calculation of static stress change, including employing a dislocation method with triangular elements rather than traditional rectangular elements, setting up a more realistic source-slip model and a more complete receiver fault model, and resolving stress changes on assumed receiver faults with spatially variable focal mechanisms based on well-determined focal mechanisms at different calculation points. The recorded aftershocks are mapped for comparison with the spatial distribution of stress changes. The results indicate that the Wenchuan earthquake encourages not only three major fault systems (the East Kunlun, south of Xianshuihe and west of Qinling Southern Frontal) but also several other regions including Tazang, north of Min Jiang, north of Pingwu-Qingchuan and west of Chongqing. In particular, the eastern segment of Longriba is shown to be quite dangerous with dramatic stress increase. The influence of depth and frictional coefficient is analyzed. The depth of calculation beyond the depth range of the source model will make a significant difference to the stress-change map and thus cannot be neglected. Many aftershocks occurring in the stress shadow zone near the main rupture can be attributed to dynamic stress triggering and the fractal structure of the main fault. The observed seismicity rate changes are compared with the static stress changes. The results show that high background seismicity rates will amplify the effect of stress change. The observed seismicity rate changes support the forecast rate of 10-year seismicity after the Wenchuan earthquake based on the rate- and state-dependent friction model. Coulomb stresses increase on the focal mechanisms away from the main rupture, which demonstrates the influence of the Wenchuan earthquake over a wide range. Especially, the focal mechanism for Lushan earthquake undergoes a stress increase by more than 2.0 bars, which suggests that the Lushan earthquake has been effectively promoted by the Wenchuan earthquake. [ABSTRACT FROM AUTHOR]

Pressure prediction has long been one of subject of research focuses in petroleum geology and exploration, but is traditionally limited to moderately overpressured formations due to disequilibrium compaction based on the empirical velocity-pressure model. Overpressures in the Xihu depression are caused by fluid expansion due to the generation of natural gas in source rocks. The resulting abnormally pressured gas reservoirs manifest as a high-pressure structure with the thick mud-coated thin sand (MCS) that remains largely unaddressed in prediction. Such gas-producing overpressures make traditional prediction methods unapplicable because of the significant influence of high gas contents on seismic velocities. We employ a frequency-dependent quality factor Q –pressure petrophysical model because of the sensitivity of acoustic attenuation to overpressures. However, acoustic attenuations from rock physics and sonic logging present an uncertain dependence on pore pressures. This implies that overpressure prediction is a typical physical system that is characterized by both deterministic mechanism and statistical behavior, which resorts to physics-informed deep learning methods. We take the Q –pressure petrophysical model as the activation function of Caianiello convolutional neurons with an attempt to combine deterministic and statistical mechanisms for overpressure prediction. Such convolutional neurons render strong feature extraction and powerful learning ability and are used to construct physics-informed Caianiello convolutional neural networks (CCNNs) for overpressure prediction in the Xihu depression. The comprehensive CCNNs-based seismic inversion scheme for overpressures consists of reservoir petrophysical modeling, deep learning for neural wavelets, well-seismic correlation analysis, deconvolution-based inversion for an initial pressure model, and input-signal reconstruction to improve the initial pressure model. With drill stem tests (DSTs), well logs, and 3D seismic data, we conduct the overpressure prediction associated with cross validation in the Xihu depression, which demonstrates the applicability of the physics-informed CCNNs inversion scheme. Predicting reliability away from the training wells usually depends on the geological complexity of areas under study. Nevertheless, the information representation in the trained CCNNs can be improved gradually by feeding new well data during the development of an oil field. • We conduct a seismic inversion for overpressure prediction using physics-informed Caianiello convolutional neural networks. • Instead of velocity, we employ quality factor Q to correlate seismic attenuation coefficients, impedances, and frequencies. • The natural gas in Pinghu Formation is migrated locally to adjacent thin sand bodies, resulting in strong overpressure. • The overpressure prediction demonstrates the applicability of joint seismic inversions by the physics-informed CCNNs. [ABSTRACT FROM AUTHOR]

Three large earthquakes (the 2007 M w 8.4 Sumatra, the 2008 M w 7.9 Wenchuan, and the 2011 M w 9.0 Tohoku) induce coseismic water-level increment at far fields (epicentral distances > 1000 km) in the Fuxin well located in the Fuxin City, northeastern China (the well with the observation of both water levels and volume strains). A comprehensive analysis for the mechanism of far-field coseismic water-level changes is performed by analyzing the in-situ permeability, Skempton's coefficient B , and with the broadband seismograms from a nearby station. We observe an undrained compaction with a decreasing permeability induced by the shaking of teleseismic waves in the far field. Shaking by teleseismic waves can induce compaction or dilatation in the aquifer of Fuxin well; is able to enhance permeability and thus build a new pore-pressure equilibrium system between the Fuxin well and the nearby Sihe reservoir (150 m away from the Fuxin well). The resulting interstitial fluid flow across the region increases coseismic water levels in the aquifer of Fuxin well. [ABSTRACT FROM AUTHOR]

Spatial sampling has a crucial influence on the horizontal resolution of seismic imaging, but how to quantify the influence is still controversial especially in complex media. Most of the studies on horizontal resolution focus on the measurement of wavelet widths for seismic migration, but neglect to evaluate the effect of side-lobe perturbations on spatial resolution. The side-lobe effect, as a migration noise, is important for seismic imaging in complex media. In this article, with focal beam analysis, we define two parameters to represent the horizontal resolution of an acquisition geometry: the width of the main lobe (WML) along the inline and crossline directions and the ratio of the main-lobe amplitude to the total amplitude (RMT) in a focal beam. We provide examples of typical acquisition geometries to show how spatial sampling affects the horizontal resolution, measured in terms of WML and RMT values. WML defines the horizontal resolution to image the target, whereas RMT describes the clarity of the imaging. Migration noise reduces with increasing RMT, indirectly improving both the vertical and horizontal resolutions of seismic imaging. Case studies of seismic migration with 3D seismic data from an oil field of China, demonstrate how the acquisition geometries with different WML and RMT values influence the performance of seismic imaging. Prior WML and RMT analyses to predict the quality of acquired datasets can optimize acquisition geometries before the implementation of seismic acquisition. [ABSTRACT FROM AUTHOR]

Abstract: For wave propagation simulation in piecewise heterogeneous media, Gaussian-elimination-based full-waveform solutions to the generalized Lippmann–Schwinger integral equation (GLSIE) are highly accurate, but involved with extremely time-consuming computations because of the very large size of the resulting boundary–volume integral equation matrix to be inverted. Several flexible approximations to the GLSIE are scaled in an iterative way to adapt numerical solutions to the smoothness of heterogeneous media in terms of incident wavelengths, with a great saving of computing time and memory. Among various typical iterative schemes to the GLSIE matrix, the generalized minimal residual method (GMRES) is an efficient approach to reduce the computational intensity to some degree. The most efficient approximation can be obtained using a Born series, as an alternative iterative solution, to both the boundary-scattering and volume-scattering waves, leading to the Born-series approximation (BSA) scheme and the improved Born-series approximation (IBSA) scheme. These iteration schemes are validated by dimensionless frequency responses to a heterogeneous semicircular alluvial valley, and then applied to a heterogeneous multilayered model by calculating synthetic seismograms to evaluate approximation accuracies. Numerical experiments, compared with the full-waveform numerical solution, indicate that the convergence rates of these methods decrease gradually with increasing velocity perturbations. The comparison also shows that the BSA scheme has a faster convergence than the GMRES method for velocity perturbations less than 10 percent, but converges slowly and even hardly achieves convergence for velocity perturbations greater than 15 percent. The IBSA scheme gives a superior performance over the other methods, with the least iterations to achieve the necessary convergence. [Copyright &y& Elsevier]

Ordovician fractured carbonates under study are over 7000 m deep in northwest China. Multistage tectonic activities result in numerous fractures along the strike-slip faults, accompanied with karst collapses due to atmospheric freshwater seepage. The resultant cave-fracture system provides numerous channels favorable for the migration and storage of hydrocarbons. Azimuthal anisotropy analyses with wide-azimuth and high-density 3D seismic data facilitate fracture estimation from migrated CRP gathers in this area. Compared with azimuthal velocity variations, azimuthal amplitude variations are quite sensitive to fractures, but suffer many negative factors. Major difficulties with azimuthal amplitudes to map superdeep fractured reservoirs include non-uniform distribution of azimuths and offsets, extremely low S/N ratio (SNR), anisotropic effect of strike-slip faults, and shielding effect of overlying irregular igneous strata. We propose an integrated scheme with azimuthal P–P amplitude/frequency attributes for prestack prediction of fractures based on the migrated CRP gathers. First, we analyze the distribution of azimuths, offsets, and bins to identify appropriate bins with the best range of offsets and the uniform distribution of azimuths. The selected wide-azimuthal CMP gathers are regrouped in terms of five azimuths, followed by azimuthal prestack migration. The resulting subazimuthal CRP gathers are optimized by denoising, flattening by residual static correction, and wavelet shaping to improve both SNR and resolution. We then conduct a local stacking in 100 m × 100 m bin for the best range of offsets from 1000 to 5600 m, followed by matched filtering to remove the footprint effect of overlying igneous strata. Frequency-related amplitude attributes are extracted for sensitive analyses in azimuths by ellipse fitting, yielding several optimal attributes for fracture prediction. We demonstrate that the coupled amplitude and frequency attributes in terms of energy percentages are the best in this area. Case studies show the applicability of the presented scheme for detecting superdeep fracture sets from extremely low SNR seismic data. • A complete processing workflow is proposed, which provides reliable basic data for prestack fracture prediction. • We analyze the effects of azimuths, offsets, bins, and folds for wide-azimuth and high-density 3D seismic acquisition, which ensure that the offsets and azimuths. • Frequency-related amplitude attributes are extracted in the azimuthal P–P migrated CRP gathers for sensitive analyses in azimuths by ellipse fitting. • Our method has a good applicability to the detection of superdeep fracture sets from extremely low SNR seismic data. [ABSTRACT FROM AUTHOR]

Abstract: Ultrasonic wave propagation in heterogeneous porous cores under laboratory studies is an extremely complex process involved with strong scattering by microscale heterogeneous structures. The resulting coda waves, as an index to measure scattering attenuation, are recorded as continuous waveforms in the tail portion of wavetrains. Because of the contamination of reflections from the side ends and reverberations between the sample surfaces, it is difficult to extract pure coda waves from ultrasonic measurements for the estimation of the P- and S-coda attenuation quality factors. Comparisons of numerical and experimental ultrasonic wave propagation in heterogeneous porous cores can give important insight into understanding the effect of boundary reflections on the P- and S-codas in the laboratory experiment. It challenges numerical modeling techniques by three major issues: the creation of a digital core model to map heterogeneous rock properties in detail, the perfect simulation with a controllable and accurate absorbing boundary, and overcoming the numerical dispersions resulting from high-frequency propagation and strong heterogeneity in material. A rotated staggered-grid finite-difference method of Biot's poroelastic equations is presented with an unsplit convolutional perfectly matched layer (CPML) absorbing boundary to simulate poroelastic wave propagation in isotropic and fluid-saturated porous media. The contamination of boundary reflections on coda waves is controlled by the CPML absorbing coefficients for the comparison between numerical and experimental ultrasonic waveforms. Numerical examples with a digital porous core demonstrate that the boundary reflections contaminate coda waves seriously, causing much larger coda quality factors and thus underestimating scattering attenuation. [Copyright &y& Elsevier]

Abstract: Prestack reverse time migration (RTM) requires extensive data storage since it computes wavefields in forward time and accesses wavefields in reverse order. We first review several successful schemes that have been proposed to reduce data storage, but require more computational redundancies. We propose two effective strategies to reduce data storage during RTM. The first strategy is based on the Nyquist sampling theorem, which involves no extra computational cost. The fact is that the time sampling intervals required by numerical algorithms or given by field records is generally several times smaller than that satisfied by the Nyquist sampling theorem. Therefore, we can correlate the source wavefields with the receiver wavefields at the Nyquist time step, which helps decrease storage of time history. The second strategy is based on a lossless compression algorithm, which is widely used in computer science and information theory. The compression approach reduces storage significantly at a little computational cost. Numerical examples show that the two proposed strategies are effective and efficient. [Copyright &y& Elsevier]

Circular RNAs (circRNAs) are formed from the genome through diverse back splicing and feature the closed loop. circRNAs are widely available in a variety of cells and characterized by conservation, structural stability, high abundance and tissue-specific or developmental-specific expression. Recent studies have shown that circRNAs are closely related to liver diseases, such as metabolic-associated fatty liver disease, hepatitis, liver cirrhosis and hepatocellular carcinoma. circRNAs play an important role in the progression of liver diseases, are potential diagnostic and prognostic markers, and have translational value in therapy. This article reviews the research on circRNAs in liver diseases, with a view to providing a theoretical basis and new ideas for future research and treatment of liver diseases. Unlabelled Image [ABSTRACT FROM AUTHOR]

The aim of the work described here was to evaluate strain and morphological change of the left ventricle in Sprague Dawley (SD) rats at different exercise intensities by 2-D speckle tracking imaging (STI). Seventy-two 8-wk-old SD rats were divided into four groups on the basis of exercise intensity: sedentary (SED), low-intensity running, medium-intensity running (MIR) and high-intensity running (HIR). Each group was further sub-divided into three groups of different exercise lengths: 1, 4 and 8 wk. The structural measurements of the left ventricle and left ventricular ejection fraction (LVEF) were obtained by echocardiography. Systolic peak values of global longitudinal, circumferential and radial strains (GLS, GCS and GRS) were obtained. Histopathological results of the cross-sectional area (CSA) of myocardial cells, collagen volume fraction (CVF) of the myocardium and perivascular collagen area (PVCA) were also observed. Structural measurements of the left ventricle and LVEF did not change with different exercise intensities or lengths. GLS of the HIR 8 wk sub-group was significantly lower than those of the SED 8 wk and MIR 8 wk sub-groups. Conversely, the GLS and GCS of the HIR 8 wk sub-group were lower than those of the HIR 1 wk and HIR 4 wk sub-groups. Histopathologically, the CSA of myocardial cells significantly increased across all HIR sub-groups and the MIR 4 wk and MIR 8 wk sub-groups. CVF endo and PVCA were also significantly increased in the HIR 4 wk and HIR 8 wk sub-groups. The HIR 8 wk group also had regional swelling and ill-defined boundaries of myocardial cells. Prolonged, high-intensity exercise may lead to exercise-induced injury of the myocardium. Two-dimensional STI can be used as a non-invasive early detection method for exercise-induced injury of myocardial function, compared with LVEF. [ABSTRACT FROM AUTHOR]

Montmorillonites are commonly existing in shales and understanding the anisotropic elastic properties of montmorillonite is very crucial because they provide important geomechanical information for the discovery and development of shale gas. Layer charges with varying densities and locations are naturally associated with montmorillonites and it has been demonstrated that these layer charge characteristics can dramatically influence the anisotropic elastic properties of dry montmorillonites. However, montmorillonites are generally hydrated by water under reservoir conditions and whether the existence of water will impact the effect of the layer charge characteristics on the anisotropic elastic properties is still poorly understood. To gain such knowledge, this paper investigated the anisotropic elastic parameters of hydrated montmorillonites with various layer charge characteristics via molecular dynamic (MD) simulations. The results demonstrated that the existence of water reduces all the elastic factors of montmorillonites, and weakens the variation of the elastic factors with different layer charge locations (LCLs), in comparison with dry montmorillonites. It was also found that when hydrated, the influence of layer charge density (LCD) on the in-plane compressional factors tends to be diminished, and the out-of-plane compressional and shear factors tend to increase consistently with increasing LCD, whereas their dependence on the LCD can be disordered in different dry montmorillonite models. The variations in the basal spacing and the interactions between the atoms caused by different layer charge characteristics when water is present were found to plausibly explain and interpret the simulation results. The results not only illustrate the link between the anisotropic elastic properties and layer charge characteristics in hydrated montmorillonites but also provide crucial geomechanical information to help the successful discovery and development of shale gas reservoirs containing hydrated montmorillonite. [ABSTRACT FROM AUTHOR]

Permeability, an important crustal property that controls transport processes in Earth's shallow crust, is known to change during large earthquakes, with significant implications on the groundwater resources and contaminant transport. Analysis of the response of groundwater in wells to Earth tides has been increasingly used to detect such changes, but often multiple interpretations of the response changes are possible, making it difficult to ascertain its hydrological implications. Here we use data from a groundwater well in North China to illustrate the use of barometric response as a method to resolve this uncertainty. The tidal response of water level in this well shows abrupt coseismic increases of both phase shift and amplitude ratio after the far-field great 2011 M w 9.1 Tohoku earthquake, which may be interpreted either as a large increase in the horizontal permeability of a confined aquifer or as an occurrence in the vertical permeability of an unconfined aquifer. Using data for the water-level response to barometric pressure we show that the aquifer was confined both before and after the Tohoku earthquake; thus the coseismic changes of the tidal response in this well are more likely to be due to an increase in the horizontal permeability. Interpretation of the tidal response shows a hereto unidentified change of poroelastic property in the far field of an earthquake, which stayed constant for ∼4 years after the earthquake until silt-cleaning in the well interrupted data collection. Thus the dynamic shaking during the Tohoku earthquake may have caused permanent deformation in the shallow crust at epicentral distances >1500 km. • The 2011 M w 9.1 Tohoku earthquake caused lasting hydrologic response in the far field. • Barometric response is used as an extra check of the post-seismic aquifer confinement. • Post-seismic hydraulic & poroelastic property changed for >4 yr in a far-field aquifer. • The earthquake may have caused permanent crustal deformation at distances >1500 km. [ABSTRACT FROM AUTHOR]

Porosity, fluid type and rock texture significantly affect acoustic wave propagation, since velocity dispersion and attenuation in fluid saturated rocks are mainly caused by wave-induced local fluid flow between microcracks and intergranular pores. We analyze P-wave velocity dispersion as a function of porosity to obtain information about the rock microstructure. The P-wave velocities in water-saturated rocks are predicted from measurements in gas-saturated rocks, using the Gassmann fluid substitution equation (the relaxed state). The dispersion is estimated from the difference between this predicted velocity and the measured one, where the latter corresponds to the unrelaxed state. We evaluate the wave dispersion as a function of porosity for 112 carbonates, 128 sandstones and 56 volcanic rocks, including our measurements for 86 tight rocks, showing that dispersion increases with porosity in the low porosity range, but decreases in the high porosity range. The dispersion peak occurs at a porosity of approximately 15%. Double-porosity poroelasticity modeling based on the local fluid-flow mechanism confirms this behavior. The microcrack radius has a peak in the porosity range 15–19% for all the lithologies from our collection, while the behavior of microcrack porosity is less evident. The dispersion peak may reveal the characteristics of lithological units, in particular porosity, fluid type and rock microstructure. • Acoustic wave dispersion peaks at a characteristic porosity around 15% for the three lithologies. • Poroelasticity modeling shows microcrack radius and porosity peak in the porosity range of 15-19%. • Different lithologies can be discriminated in tight rocks by the relations between dispersion and porosity. [ABSTRACT FROM AUTHOR]

It is important to understand how magnetotelluric (MT) modeling can most effectively be performed in general anisotropic media. However, previous studies in this area have mainly focused on the use of one-dimensional (1D) and two-dimensional (2D) algorithms. Thus, building on earlier work, it is important to study the performance of three-dimensional (3D) modeling in arbitrary conductivity media; therefore, an edge-based finite element (FE) method has been developed for 3D MT modeling in arbitrary conductivity media. This approach is based on the initial derivation of a series of equivalent variational equations that are based on Maxwell equations, generated using the weighted residual method. Specific values were then obtained for coefficient matrixes of this edge-based FE method using hexahedral meshes, and the algorithm was verified by comparing its results with finite difference (FD) solutions generated using a 2D anisotropic model. Finally, the results of a 3D anisotropic model were analyzed detailed for three conditions; another 3D anisotropic model was designed and its results were compared with two isotropic models'. [ABSTRACT FROM AUTHOR]

Ozone (O 3) is characteristic of high oxidative activity. It displays a high potential value in sterilization and decontamination. Although O 3 has been widely investigated for its efficiency and environmentally friendly effectiveness, the fundamental issue regarding the complicated microscopic interaction mechanism between O 3 and contaminant molecules remains largely unaddressed. We addressed this knowledge gap through molecular dynamics (MD) simulation at the molecular scale. Results indicated that five representative hydrocarbon molecules (n -hexadecane, phytane, terpane, naphthalin and acenaphthylene) on a rough silica (SiO 2) surface were almost removed after about 300 ps simulation. And the aromatic molecules were easier to be removed than aliphatic ones. The hydroxyl oxidation reaction was demonstrated as a predominant mechanism. As the large dose of O 3 was supplied by atmospheric air dielectric barrier discharge (DBD) plasma, this work provided an important theoretical reference for better using plasma technology for oily contaminant removal. [Display omitted] • MD simulation addressed the complicated microscopic interaction processes. • Almost all of five hydrocarbon molecules were removed by O3 in 300 ps simulation time. • The hydroxyl oxidation reaction was demonstrated as a predominant removal mechanism. • This work helps plasma communities better use air plasma on oily contaminant removal. [ABSTRACT FROM AUTHOR]

• This work proposed a deep encoder-decoder neural network (DEDNN) for predicting TOC contents. • The DEDNN model shows more accurate and sensitive than ΔLogR method and CNN method. • The DEDNN model can highlight the contribution of individual logging curve to the TOC prediction. Total organic carbon (TOC) content is an important geochemical parameter for evaluating the hydrocarbon generation potential of unconventional oil and gas resources. The TOC content of source rocks significantly affects the responses of well logs so, in principle, well logs can be used for source rock appraisal. However, the complex relationships between TOC content and well logs involve nonlinear mapping with many parameters. It is sometimes difficult to obtain continuous and accurate TOC content values using conventional methods such as the ΔLogR method. In this study, we propose a TOC prediction model using a deep encoder-decoder neural network (DEDNN) based on mining and mapping of multiscale features of logging curves. The prediction performance of the model is validated by a series of tests using data from four exploration wells in the Longmaxi black shale in the Dingshan area of the Sichuan Basin. The TOC content prediction results confirm that the proposed DEDNN is more accurate than either the ΔLogR method or CNN, which is a state-of-the-art convolutional neural network. Furthermore, a saliency map derived from the DEDNN results shows the relative importance of different well logs to TOC contents. [ABSTRACT FROM AUTHOR]

The composition of formation waters in the Dongying Depression provide important clues about regional water-rock interactions. Chemical analysis (181 samples) of formation waters form the Shahejie Fm (58 wells) in the Niuzhuang oilfield suggest two main geochemical facies, the chloride-magnesium (Cl–Mg) and bicarbonate-sodium (HCO 3 –Na) facies (pH = 7.8 ± 0.9) that have low salinity (TDS = 7.3 ± 7.8 g/L) and occurs within source rocks, and the Cl–Ca facies (pH = 6.5 ± 0.7) that has high salinity (TDS = 79.1 ± 79.0 g/L) and occurs within clastic reservoirs. For the water within the clastic reservoirs, salinities and dissolved chloride concentrations (47.8 ± 48.8 g/L) are attributed to halite dissolution. The broad systematic increase in dissolved Mg2+ and Ca2+, and decrease in pH with increasing salinity (Na+ concentration) strongly suggest that the formation water has been thermodynamically buffered by silicate-carbonate mineral assemblages. The Ca excess increase with Na deficit suggests that the albitization of detrital plagioclase (anorthite) might have provided a internal source for Ca2+. The pH was mainly buffered by silicate minerals, which is indicated by the increase of acidity with Na+. This is also consistent with the externally buffered carbonate system indicated by the negative correlation of log(HCO 3 −) with log(Ca2+). The increasing acidity associated with the addition of Na+ might have been responsible for the abundant kaolinite and secondary porosity developed by K-feldspar dissolution. The contribution from halite dissolution to formation waters within the source rocks was relatively restricted. The positive correlation of log(HCO 3 −) with log(Ca2+) suggests an internally buffered carbonate system. The formation water might have been partly buffered by illitization, which is consistent with the negative correlation of Na deficit with Ca excess. • Two hydrogeochemical facies are recognized in the source rock and clastic reservoirs. • Waters are well buffered by silicate-carbonate mineral assemblages. • Halite dissolution and water-rock interaction control water composition. • Saline water injection might be responsible for secondary porosity. [ABSTRACT FROM AUTHOR]

Tight sandstones usually present great variations in Archie's exponents due to their high clay contents and multi-scale pores. Conventional multi-scale digital rocks consider the effect of micro and macro pores but ignore the contribution of clay minerals to electrical conductivity, whereas traditional multi-mineral digital rocks cannot consider the contribution of micro pores. We propose an upscaling method to construct complex digital rocks for accurate estimation of electrical conductivities. Based on a 3-D grayscale image of a tight sandstone acquired by X-ray CT and a 2-D mineralogy slice imaged by energy-dispersive SEM (EDS-SEM), we reconstruct a 3-D multi-mineral digital rock that is composed of intergranular pores and mineral phases by image registration and multi-threshold segmentation. Fine mineral structures and micro pores are revealed by the multi-scale imaging technique. The effective conductivity of each mineral phase associated with a specific micro porosity is calculated by the Archie's equation or Waxman-Smits model. By assigning each voxel with the optimal conductivity according to its mineral phase, we estimate the bulk electrical conductivity of the entire digital rock by the finite element method. The contributions of fluids and clay minerals to the bulk electrical properties are implicitly incorporated into the numerical simulation without increasing computational cost. The upscaling method is validated by experimental measurements of formation factors. We investigate the effect of clay minerals and scanning resolutions on the calculated electrical conductivities with attempt to interpret variations in the cementation exponent. • Fine structures of main minerals are revealed by multi-scale imaging techniques. • Digital rocks have similar porosities and proportions of minerals to tight rocks. • Formation factors are accurately calculated by the proposed upscaling method. [ABSTRACT FROM AUTHOR]

Cracks that are widely existing in geological formations play an important role in affecting the elastic and electrical rock properties, which are remotely measured for detecting and characterizing cracked rocks. Joint interpretation of the complementary elastic and electrical data is expected to give a better assessment of the cracks. However, the correlations between the elastic and electrical rock properties, which are the key to the successful joint interpretation, remain poorly understood in layered porous rocks with cracks of varying orientations. We reviewed and summarized the most recent advances in the theoretical models for the elastic and electrical properties of layered porous rocks with inclined and rotated cracks as well as with randomly orienting cracks. The limitations of the models were identified by comparing the modeling results with available experimental data, and we applied the models within their validity range to obtaining theoretically the correlations between the elastic and electrical properties in layered porous rocks with cracks of the above-mentioned orientations, in the horizontal and vertical directions, respectively. We showed that the elastic and electrical properties are systematically correlated with cracks of varying crack densities and aspect ratios, different cracks orientations affect the correlations in varying ways. The results not only illustrate the link between the elastic and electrical properties in cracked rocks but also have important practical applications when the seismic and electromagnetic exploration data are jointly interpreted to gain better knowledge about the subsurface Earth, although future work is required to extend the models to more realistic cracked formations and to experimentally test the validity of the models and the theoretically obtained joint correlations. [ABSTRACT FROM AUTHOR]

The double-porosity theory of wave propagation in rocks considers a single scale based on soft and stiff pores, and wave attenuation occurs by local fluid flow between these pores. However, rocks exhibit more complicated fabric structures, with heterogeneities presented at multiple scales, having a self-similar fractal nature as reported. We develop a poroelasticity model to describe wave anelasticity in a fluid-saturated medium consisting of infinite components, i.e., an infinituple-porosity medium. Numerical modeling is achieved with infinite iterations, where at each iteration one component is added (a porous inclusion embedded in a porous host), analogous to the differential effective medium (DEM) theory of solid composites. By considering the self-similar structure, the properties of each component (inclusions) are scale-dependent. The example shows that the P-wave velocity dependence on frequency depends on the fractal dimension. Application of the model to sandy sea-bottom sediments shows a good agreement, with fractal dimension of 2.88. [ABSTRACT FROM AUTHOR]

Wave propagation in rocks induces fluid pressure gradients and flow between stiff intergranular pores and compliant microfractures. This, in turn, leads to wave anelasticity, i.e., attenuation and velocity dispersion. Three known squirt-flow models attempt to explain this phenomenon. Based on these theories, we reformulate a new one, where we derive the dry-rock moduli on the assumption that the boundary fluid pressure is constant. The new model improves the predictions of the other models, e.g., a better description at high frequencies and the inclusion of permeability effects. The numerical example shows the response due to the characteristic squirt-flow length and fluid viscosity on wave propagation. The reformulated model is applied to experiments made on water-saturated tight sandstones, where the squirt-flow length is determined, showing that it increases with increasing permeability and porosity at full saturation. • A new squirt-flow model by deriving the dry-rock moduli on the assumption of the constant boundary fluid pressure. [ABSTRACT FROM AUTHOR]