Abstract
An experimental system based on the fluid–structure coupling method is established to link the fracture surface with the change of seepage field, and the seepage mechanism of bifurcation fractures under confining pressure is expounded. It is found that the relationship between hydraulic slope (J) and flow volume (Q) appears as an upward convex function as the effective permeability (ke) increases gradually with J. As inlet flow gradually increases, the rising rate of hydraulic slope gradually weakens. Under the action of confining pressure at all levels, there will be a greater closing effect on the side of the bifurcation fracture with a larger bifurcation angle, thereby promoting seepage of the deflection fluid in the other side of the fracture. The load and contact area of the bifurcation fracture surfaces under confining pressure, measured by pressure film, hinder the fluid flow, which is the main reason for the deflection flow behavior of the fluid. The mechanical behavior of the fracture surfaces under confining pressure is such that the microconvex contacts occur first and then the contact process radiates to the surrounding media, forming contact areas with different loads. Deflection flow behavior caused by the fracture contact under confining pressure has positive significance for research on seepage characteristics.
Résumé
Un système expérimental basé sur la méthode de couplage fluide-structure est établi pour relier la surface de la fracture au changement du champ d’infiltration, et le mécanisme d’infiltration des fractures de bifurcation sous pression de confinement est expliqué. On constate que la relation entre la pente hydraulique (J) et le volume d’écoulement (Q) prend la forme d’une fonction convexe ascendante, la perméabilité effective (ke) augmentant progressivement avec J. Lorsque le débit d’entrée augmente progressivement, le taux d’augmentation de la pente hydraulique s’affaiblit peu à peu. Sous l’action de la pression de confinement à tous les niveaux, l’effet de fermeture sera plus important du côté de la fracture de bifurcation présentant un angle de bifurcation plus grand, ce qui favorisera l’infiltration du fluide de déviation de l’autre côté de la fracture. La charge et la zone de contact des surfaces de fracture de bifurcation sous la pression de confinement, mesurée par le film de pression, entravent l’écoulement du fluide, ce qui est la principale raison de promouvoir le comportement d’écoulement de déviation du fluide. Le comportement mécanique des surfaces de fracture sous pression de confinement est tel que les contacts microconvexes se produisent d’abord, puis le processus de contact rayonne vers les milieux environnants, formant des zones de contact avec des charges différentes. Le comportement d’écoulement par déviation causé par le contact de fracture sous la pression de confinement est d’une importance positive pour la recherche sur les caractéristiques d’infiltration.
Resumen
Para relacionar la superficie de fractura con el cambio del campo de infiltración se establece un sistema experimental basado en el método de acoplamiento fluido-estructura, y se expone el mecanismo de infiltración de las fracturas por bifurcación bajo presión de confinamiento. Se encuentra que la relación entre la pendiente hidráulica (J) y el volumen de flujo (Q) aparece como una función convexa ascendente a medida que la permeabilidad efectiva (ke) aumenta gradualmente con J. A medida que el flujo de entrada aumenta gradualmente, la tasa de aumento de la pendiente hidráulica se atenúa gradualmente. Bajo la acción de la presión de confinamiento en todos los niveles, habrá un mayor efecto de cierre en el flanco de la fractura de bifurcación con un mayor ángulo y, por lo tanto, se promoverá la filtración del fluido de desviación en el otro flanco de la fractura. La carga y el área de contacto de las superficies de la fractura de bifurcación bajo presión de confinamiento, medida por la película de presión, dificultan el flujo de fluido, que es la razón principal para promover el comportamiento de flujo de desviación del fluido. El comportamiento mecánico de las superficies de fractura bajo presión de confinamiento es tal que primero se producen los contactos microconvexos y luego el proceso de contacto se irradia a los medios circundantes, formando zonas de contacto con diferentes cargas. El comportamiento del flujo de desviación causado por el contacto de la fractura bajo presión de confinamiento tiene una importancia positiva para la investigación de las características de la infiltración.
摘要
基于流固耦合方法的实验系统建立,将裂隙面与渗流场的变化联系起来,并阐述了在围压作用下分岔裂缝的渗流机理。研究发现,随着有效渗透率(ke)逐渐增大,水力坡度(J)与流量(Q)之间的关系呈现出上凸函数的形式。随着入口流量逐渐增加,水力坡度的增长速率逐渐减弱。在不同围压水平下,对于具有较大分岔角的分岔裂缝一侧,围压会产生更大的闭合效应,从而促进裂缝的偏转流体渗流。通过压力膜测量,围压下的分岔裂缝面负载和接触区域会阻碍流体流动,这是促进流体偏转流动行为的主要原因。围压下的断裂面的力学行为表现为先发生微凸接触,然后该接触过程向周围介质辐射,形成具有不同载荷的接触区域。在围压下,由裂缝接触引起的偏转流动行为对渗流特性的研究具有积极意义。
Um sistema experimental baseado no método de acoplamento fluido-estrutura é estabelecido para relacionar a superfície de fratura com a mudança do campo de infiltração, além de expor o mecanismo de infiltração de fraturas de bifurcação sob pressão confinante. Verifica-se que a relação entre o gradiente hidráulico (J) e o volume de fluxo (Q) aparece como uma função convexa ascendente à medida que a permeabilidade efetiva (ke) aumenta gradualmente com J. À medida que o fluxo de recarga aumenta gradualmente, a taxa de aumento do gradiente hidráulico diminui gradualmente. Sob a ação da pressão de confinamento em todos os níveis, haverá um maior efeito de fechamento no lado da fratura de bifurcação com um ângulo de bifurcação maior, promovendo assim a infiltração do fluido de deflexão no outro lado da fratura. A carga e a área de contato das superfícies de fratura de bifurcação sob pressão confinante, medidos por filme de pressão, impedem o fluxo de fluido, que é a principal razão para promover o comportamento de fluxo de deflexão do fluido. O comportamento mecânico das superfícies de fratura sob pressão confinante é tal que os contatos microconvexos ocorrem primeiro e, em seguida, o processo de contato se irradia para os meios circundantes, formando áreas de contato com diferentes cargas. O comportamento de fluxo de deflexão causado pelo contato da fratura sob pressão confinante tem significado positivo para pesquisas sobre características de infiltração.
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The data that support the findings of this study are available from the corresponding author upon reasonable request.
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This work was supported by the National Natural Science Foundation of China (Grant Nos. 41831289, 41772250, and 42072276). The authors thank the anonymous reviewers for their helpful comments and suggestions.
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Ma, H., Feng, P., Qian, J. et al. Study on the seepage mechanisms of rock with bifurcation fractures under confining pressure. Hydrogeol J 31, 1701–1713 (2023). https://doi.org/10.1007/s10040-023-02669-8
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DOI: https://doi.org/10.1007/s10040-023-02669-8