Upscaling of two-phase discrete fracture simulations using a convolutional neural network

Upscaling methods such as the dual porosity/dual permeability (DPDP) model provide a robust means for numerical simulation of fractured reservoirs. In order to close the DPDP model, one needs to provide the upscaled fracture permeabilities and the parameters of the matrix-fracture mass transfer for every fractured coarse block in the domain. Obtaining these model closures from fine-scale discrete fracture-matrix (DFM) simulations is a lengthy and computationally expensive process. We alleviate these difficulties by pixelating the fracture geometries and predicting the upscaled parameters using a convolutional neural network (CNN), trained on precomputed fine-scale results. We demonstrate that once a trained CNN is available, it can provide the DPDP model closures for a wide range of modeling parameters, not only those for which the training dataset has been obtained. The performance of the DPDP model with both reference and predicted closures is compared to the reference DFM simulations of two-phase flows using a synthetic and a realistic fracture geometries. While the both DPDP solutions underestimate the matrix-fracture transfer rate, they agree well with each other and demonstrate a significant speedup as compared to the reference fine-scale solution.

     

Annama H chondrite—Mineralogy,physical properties,cosmic ray exposure,and parent body history

The fall of the Annama meteorite occurred early morning (local time) on April 19, 2014 on the Kola Peninsula (Russia). Based on mineralogy and physical properties, Annama is a typical H chondrite. It has a high Ar‐Ar age of 4.4 Ga. Its cosmic ray exposure history is atypical as it is not part of the large group of H chondrites with a prominent 7–8 Ma peak in the exposure age histograms. Instead, its exposure age is within uncertainty of a smaller peak at 30 ± 4 Ma. The results from short‐lived radionuclides are compatible with an atmospheric pre‐entry radius of 30–40 cm. However, based on noble gas and cosmogenic radionuclide data, Annama must have been part of a larger body (radius >65 cm) for a large part of its cosmic ray exposure history. The ¹⁰Be concentration indicates a recent (3–5 Ma) breakup which may be responsible for the Annama parent body size reduction to 30–35 cm pre‐entry radius.     

Stability issues of the continuous welded rail track on the concrete sleepers on the curves with radius R ≤ 300 m

This paper describes the economic and technological benefits of installing continuous welded rail(CWR) track on sharp(radius ≤ 300 m) railway curves. A new form of prestressed concrete sleepers developed by the V. Lazaryan Dnipropetrovsk National University of Railway Transport is shown to improve the lateral shift resistance of CWR track in sharp curves and the use of anchor sleepers on tangents is shown to make it possible to lower the fastening temperature of the CWR track in order to increase the rail lifespan.     

Kinetics of dissolution of mechanically comminuted rock-forming oxides and silicates—II. Deformation and dissolution of oxides and silicates in the laboratory and at the Earth's surface

Comparison of the patterns of fracture under tensile stress, indentation, and scratching of periclase. quartz, and corundum indicates that the properties relevant to dissolution of rock-forming oxides and of rock-forming non-layer silicates should be changed by mechanical comminution in essentially the same way as those of quartz. The changes are accomplished by brittle fracture under the tensile component of the stress field, which does not generate subsurface damage, and by microplastic behavior under local stresses with high net compressive and shear components, which does.Mechanical comminution should therefore affect the apparent rates of dissolution (rates calculated with respect to the initial interface area) of rock-forming oxides and of rock-forming non-layer silicates in essentially the same way in which it affects the apparent rate of dissolution of quartz. This is supported by the available evidence on the effect of dry grinding on the kinetics of dissolution of feldspars, pyroxenes, and olivines in aqueous solutions.Different effects of mechanical comminution on solubilities and dissolution rate constants can be related to certain measured or calculated properties of the considered minerals. Notably, the effect of grain size on the dissolution rate constant can be rigorously related to the Kelvin effect.The available evidence on the mechanical comminution at the bases of dry-based glaciers in highgradient segments of streams, in certain high-energy coastal and epeiric environments, and in sandy deserts indicates that such mechanical comminution should significantly affect the simultaneous or subsequent dissolution of the comminuted material.     

Phytoplankton in the south-western Kara Sea: composition and distribution

The taxonomic composition and spatial distribution of pelagic algae were studied in the south-western Kara Sea in August-September 1981. In the north-western and easternmost regions of the study area the phytoplankton community, dominated by neritic diatoms and autotrophic dinoflagellates, was at the late spring bloom stage of the seasonal succession. In the central deep-water zone of the sea, there was a predominance of heterotrophic dinoflagellates from the genera Protoperidinium and Dinophysis , and the autotrophic compartment of the algal community was clearly in a stage of decline. The distribution of the phytoplankton assemblages followed closely the major routes of receding marginal ice zones. Three stages of the seasonal succession were established for the area of interest: (1) early spring (ice edge) bloom of arcto-boreal neritic diatoms; (2) late spring bloom of neritic diatoms and autotrophic dinoflagellates, fuelled by continental run-off; and (3) summer minimum with a predominance of heterotrophic dinoflagellates, followed by autumnal decline of the phytoplankton community.     

Index and Composites of the Kuroshio Meander South of Japan

Using the merged NOAA National Oceanographic Data Center (NODC)/Japan Oceanographic Data Center (JODC)/Marine Information Research Center (MIRC) historical hydrographic dataset, a new Kuroshio large meander (LM) index is introduced. This index helps to distinguish between the LM events and other types of Kuroshio Current (KC) variability south of Japan. Observations, re-systematized according to the index, provide composite patterns of typical formation and decay of the LM. The patterns reveal a remarkable similarity between individual LMs and support the deterministic rather than the stochastic model of LM evolution on a time-scale of one year. A “trigger” meander (TM) occurs on composite maps six months prior to the LM formation as a 1° latitude southward shift of the KC axis south of Kyushu. When propagating eastward along the coast of Japan, TM gradually increases in area. In principal the emergence of LM takes only one month. East of TM and LM a remarkable onshore shift of the KC is noticed, supplying the coastal region with warm water. Other warm anomalies are found on the warm side of KC next to the propagating TM and in the larger warm eddy area southeast of Kyushu. Different LMs survive for different times and decay in some months after KC “jumps” across the Izu Ridge. Changes of water properties on isopycnals in the interior of LM can be roughly described by two-layer kinematics with an interface at σ_θ = 27 which suggests a strong inflow of deep Kuroshio waters into the LM core during the formation of the latter. This revised version was published online in August 2006 with corrections to the Cover Date.     

Western Palaearctic palaeoenvironmental conditions during the Early and early Middle Pleistocene inferred from large mammal communities,and implications for hominin dispersal in Europe

Large-scale fluctuations in global climate and resulting changes in ecology had a profound effect on human evolution and dispersal. Though hominin remains are scarce, studies focussing on the more abundant records of fossil land mammal communities can contribute greatly to our knowledge of the palaeoenvironmental circumstances that influenced and directed the global spread of hominins. To produce a comprehensive and accurate account of the evolution of western Palaearctic habitat diversity between 2.6 and 0.4 Ma BP, information generated from large mammal communities from 221 key sites has been included in this study.The palaeoecological conditions of the western Palaearctic during the Early and early Middle Pleistocene were principally controlled by the following key factors: (1) a widespread trend of temperature decrease, (2) the periodicity of the global temperature record, (3) the intensity of single climatic stages, (4) the temporal pattern of climatic variation, (5) geographical position, and (6) the distribution of continental water resources. A general picture of the evolution of western Palaearctic habitat diversity saw the replacement of extensive forested terrain by an alternating sequence of varied savannah-like and forested habitats during the 2.6–1.8 Ma span, as well as an alternation between different types of predominantly open habitats between 1.8 and 1.2 Ma. Both of these processes were governed by 41 ka temperature periodicity. During the 1.2–0.9 Ma time span, irregular climatic fluctuations were more common and habitat variability increased. The subsequent 0.9–0.4 Ma interval, a period controlled by 100 ka periodicity, was by comparison more stable, with longer climatic cycles alternating between open and forested landscapes. During the entire Early and early Middle Pleistocene, assemblages of large mammal communities reveal a distinct trend of decreasing continentality between Eastern and South-Eastern Europe on the one hand, and South-Western and North-Western Europe on the other. This trend was due to the effect of the Atlantic Ocean, while in Southern Europe the relatively low continentality was balanced by influences from the Mediterranean Sea.When plotted against evidence of hominin occurrence, the data on western Palaearctic habitat diversity inferred from large mammal communities indicate clear environmental stimuli for the earliest human dispersal in Europe. These are: (1) a wide range of habitats, implying a high diversity of resources; (2) mild climates with low seasonality, implying a lack of strong environmental fluctuations. Around 1.8 Ma at the latest, hominins of African origin entered the western Palaearctic for the first time, taking advantage of the diversity of habitats and resources, particularly along large river systems. Their subsequent westward spread between 1.7 and 1.3 Ma was restricted to Mediterranean-influenced areas, which offered a high variability of habitats and relatively low seasonality. The increase in environmental diversity, which occurred from 1.2 Ma onwards, opened up South-Eastern and Eastern Europe for hominin occupation. According to the available records, North-Western and Central Europe were initially colonized during late Early to early Middle Pleistocene interglacials, when these regions experienced periods of low seasonality and considerable habitat diversity.