Characterization Method and Application of Heterogeneous Reservoir Based on Different Data Quantity

Deep saline aquifers have strong heterogeneity under natural conditions, which affects the migration of carbon dioxide (CO2) injection into the reservoir. How to characterize the heterogeneity of rock mass is of great significance to research the CO2 migration law during CO2 storage. A method is proposed to construct different heterogeneous models from the point of view of whether the amount of data is sufficient or not, the wholly heterogeneous model with sufficient data, the deterministic multifacies heterogeneous model which is simplified by lithofacies classification, and the random multifacies heterogeneous model which is derived from known formation based on transfer probability theory are established, respectively. Numerical simulation is carried out to study the migration law of CO2 injected into the above three heterogeneous models. The results show that the migration of CO2 in heterogeneous deep saline aquifers shows a significant fingering flow phenomenon and reflect the physical process in CO2 storage; the migration law of CO2 in the deterministic multifacies heterogeneous model is similar to that in the wholly heterogeneous model and indicates that the numerical simulation of simplifying the wholly heterogeneous structure to the lithofacies classification structure is suitable for simulating the CO2 storage process. The random multifacies heterogeneous model based on the transfer probability theory accords with the development law of sedimentary formation and can be used to evaluate the CO2 migration law in unknown heterogeneous formations. On the other hand, by comparing the dry-out effect of CO2 in different heterogeneous models, it is pointed out that the multifacies characterization method will weaken the influence due to the local homogenization of the model in small-scale research; it is necessary to refine the grid and subdivide the lithofacies of the local key area elements to eliminate the research error. The research results provide feasible references and suggestions for the heterogeneous modeling of the missing data area and the simplification of large-scale heterogeneous models.

A gas migration law study of a large-scale 3D physical similarity simulation with an adaptive Kalman filter algorithm

Purpose In this study, a physical similarity simulation plays a significant role in the study of crack evolution and the gas migration mechanism. A sensor is deployed inside a comparable artificial rock formation to assure the accuracy of the experiment results. During the building of the simulated rock formation, a huge volume of acidic gas is released, causing numerous sensor measurement mistakes. Additionally, the gas concentration estimation approach is subject to uncertainty because of the complex rock formation environment. As a result, the purpose of this study is to introduce an adaptive Kalman filter approach to reduce observation noise, increase the accuracy of the gas concentration estimation model and, finally, determine the gas migration law. Design/methodology/approach First, based on the process of gas floatation-diffusion and seepage, the gas migration model is established according to Fick’s second law, and a simplified modeling method using diffusion flux instead of gas concentration is presented. Second, an adaptive Kalman filter algorithm is introduced to establish a gas concentration estimation model, taking into account the model uncertainty and the unknown measurement noise. Finally, according to a large-scale physical similarity simulation platform, a thorough experiment about gas migration is carried out to extract gas concentration variation data with certain ventilation techniques and to create a gas chart of the time-changing trend. Findings This approach is used to determine the changing process of gas distribution for a certain ventilation mode. The results match the rock fissure distribution condition derived from the microseismic monitoring data, proving the effectiveness of the approach. Originality/value For the first time in large-scale three-dimensional physical similarity simulations, the adaptive Kalman filter data processing method based on the inverse Wishart probability density function is used to solve the problem of an inaccurate process and measurement noise, laying the groundwork for studying the gas migration law and determining the gas migration mechanism.

The paradigm of the migration crisis and its influence on national legislation on irregular migration

The aim of this article is to provide a detailed study of the ways in which the paradigm of crisis has influenced the law and practice of European countries in the field of irregular migration. Bearing in mind that the perception of “crisis” is ambiguous and does not have legal definition, the first part of this paper will provide a clarification of its scope and some contexts in which it is used. Secondly, labelling some situations as “crises” requires some urgent and unusual actions. Hence, it is important to indicate what types of legal measures and normative solutions, therefore, prevail nowadays in the practice of states. The countries that are particularly interesting in this context include Germany, Sweden, and Denmark, whose migration policies have, over the course of the past few years, decisively shifted from a relatively open approach towards more restrictive solutions. Although the crisis in the migration context is defined bipolarly, a characteristic feature of the paradigm shift is focusing on the elimination or at least limitation of the presence of foreigners on the territory of the statethrough border controls, obstruction of access to international protection and family reunification, as well as increasing the effectiveness of forced returns. The result of these consideration has led to the conclusion that on the one hand the authorities’ rhetoric of crisis not automatically mean the use of special and emergency measures foreseen by law. On the other hand, the narrative referring to defeat and catastrophe justified the introduction of controversial solutions in a hurry, often with disregard for the detailed analyses and regulatory impactassessment, which are common in such cases. At the same time, the determinant of the shape of the migration law is the “temporariness” inherent in the crisis paradigm. One of its most important elements is the departure from long-term residence permits, guaranteeing a certain stability in connection with international protection, in favour of short-term permits.

The migration law of magnesium ions during freezing and melting processes

To explore the migration law of magnesium ions (Mg2+) during freezing and melting processes, laboratory simulation experiments involving freezing and melting were carried out to investigate the influence of ice thickness, freezing temperature, initial concentration, and initial pH on the distribution of Mg2+ in the ice-water system. The distribution coefficient “K” (the ratio of the Mg2+ concentration in the ice layer to the Mg2+ concentration in the water layer under ice) was used to characterize the migration ability of Mg2+. The results showed that during the freezing process, the concentration distribution of Mg2+ in the ice and water two-phase system was as follows: ice layer < water before freezing < water layer under ice; in other words, it migrated from ice layer to the water layer under ice. “K” decreased with increasing ice thickness, freezing temperature, initial concentration, and initial pH; the higher the ice thickness, freezing temperature, initial concentration, and initial pH were, the higher the migration efficiency of Mg2+ into the water layer under ice was. During the melting process, Mg2+ was released in large amounts (50–60%) at the initial stage (0–25%) and in small amounts (25–100%) uniformly in the middle and later periods. According to the change of Mg2+ concentration in ice melt water, an exponential model was established to predict Mg2+ concentration in ice melt period. The migration law of Mg2+during the freezing and melting process was explained by using first principles.

Migration and Distribution Characteristics of Proppant at the Corner of Horizontal Fracture Network in Coal Seam

A complex fracture network is composed of many similar structures. The migration law of proppant at each structure is the core and basic content of the migration law of proppant in complex fracture network, and there is little research. In this study, the EulerianEulerian method (TEM) is used to analyze the migration and distribution characteristics of solid–liquid two phases at the fracture corner according to different corner types of the fracture network. The results show that the migration characteristics of proppant in the corner area can be divided into the corner anomaly area, buffer area, and stability area; the influence of the turning angle on proppant migration is mainly concentrated at the corner and in the range of 4 times the fracture width after turning. The probability of sand plugging at the corner of the “Y → T” fracture is lower than that of “L → l”, higher than that of the “X → +” wing branch fracture, and lower than that of the main fracture. At the corner of the fracture network, after the solid flow turns, the proppant will form a high sand area on the side of the impact fracture surface, then rebound back to the fracture, form a sand-free area on the other side, and form a high-velocity core in the refraction interval. At the corner of the “L → l” fracture, there are one high sand area, one non-sand area, two low-velocity areas, and one high-velocity area; there are three low-velocity areas, two sand-free areas, and one high sand area at the corner of the “Y → T” fracture; at the corner of the “X → +” fracture, there is a high sand area and no sand-free area, and the flow velocity of the main fracture is much greater than that of the wing branch fracture.

Race and the regulation of international migration. The ongoing impact of colonialism in the case law of The European Court of Human Rights

In the case law of the European Court of Human Rights (ECtHR) the right of States to control migration is firmly established despite strong indications that the effects of migration control are not racially neutral. In this article we attempt to understand how it is possible that the doctrine of sovereign migration control is not considered to breach the prohibition of racial discrimination. We argue that the ECtHR’s approach to migration and racial discrimination fits a pattern in the historical development of migration law whereby the right to travel, and the power of States to restrict this right, have been consistently defined in such a way as to protect the interests of the predominantly white population of today's global North. Hence, the ease with which the racialised impact of migration control is accepted as normal and compatible with the prohibition of racial discrimination is consistent with migration law's long history as part of colonial and postcolonial relations.

Exploring the trajectories of highly skilled migration law and policy in Japan and the UK

Japan and the UK appear to have few commonalities in terms of their history of and approach to migration law and policy. However, strong similarities in their contemporary approaches can be detected. Migration sits at the very top of the national political agendas and both have undertaken successive, major policy reforms over the past decade. Both have governments publicly committed to policies to attract ‘highly skilled’ migrants, with a restrictive approach towards ‘unskilled’ migrants. This article draws out the similarities and differences of migration law and policy in Japan and the UK via their respective legislative structures and policy trajectories on highly skilled migration. The article argues that Japan and the UK promote a market-driven model which enables highly skilled migration to be ‘sold’ to publics believed to be hostile to increased migration. Yet, the rapid changes in policy and revising of applicable rules often prevents the successful recruitment of highly skilled migrants to both countries.