Abstract
To investigate two-phase fluid flow processes influenced by phase interference, pressure drop, fracture roughness and environmental stress, a nitrogen-water two-phase flow experiment was carried out on highly rough granite fractures in an experimental triaxial cell. Pressure was used to control the two-phase fluid in the fracture. The results show that each fluid phase has a separate flow channel, even through rock fractures of large roughness. Correlation of the superficial velocities of the two-phase fluids identifies the annular flow at a high pressure drop due to the high kinetic energy of the gas phase; however, annular flow transitioned to complex flow with increasing fracture roughness and confining pressure. The relative permeability of water is greater than that of gas. The sum of the relative permeabilities of the two phases is less than unity due to phase interference. With increasing pressure head, confining pressure, and fracture roughness, the relative permeability of water shows a general decreasing trend and the sum of relative permeability continuously reduced, demonstrating that the localized flow paths of the different phases changed and the phase interference increased. The experimental relative permeability of gas is greater here than that determined by the nonlinear viscous coupling model and Corey model, but less than the straight-line relative permeability model (X-model). Among them, the viscous coupling model provides the closest approximation, indicating that the physical process of two-phase flow through highly rough and tight rock fractures is more like that through a pipe, rather than through porous media and parallel-plate channels.
Résumé
Afin d’étudier les processus d’écoulement de fluides diphasiques influencés par l’interférence des phases, la chute de pression, la rugosité des fractures et les contraintes environnementales, une expérience d’écoulement diphasique azote-eau a été réalisée sur des fractures de granite très rugueuses dans une cellule triaxiale expérimentale. La pression a été utilisée pour contrôler le fluide diphasique dans la fracture. Les résultats montrent que chaque phase fluide possède un canal d’écoulement distinct, même à travers des fractures rocheuses de grande rugosité. La corrélation des vitesses superficielles des fluides diphasiques permet d’identifier l’écoulement annulaire en condition de forte chute de pression due à l’énergie cinétique élevée de la phase gazeuse. Cependant, l’écoulement annulaire évolue vers un écoulement complexe avec l’augmentation de la rugosité de la fracture et de la pression de confinement. La perméabilité relative de l’eau est plus grande que celle du gaz. La somme des perméabilités relatives des deux phases est inférieure à l’unité, à cause de l’interférence de phase. Avec l’augmentation de la pression, de la pression de confinement et de la rugosité des fractures, la perméabilité relative de l’eau présente une tendance générale à la baisse et la somme des perméabilités relatives diminue de manière continue, ce qui montre que les voies d’écoulement localisées des différentes phases ont changé et que l’interférence des phases a augmenté. La perméabilité relative expérimentale du gaz est ici supérieure à celle déterminée par le modèle de couplage visqueux non linéaire et le modèle de Corey, mais inférieure au modèle de perméabilité relative linéaire (modèle-X). Parmi les modèles, le modèle de couplage visqueux fournit l’approximation la plus proche, ce qui indique que le processus physique de l’écoulement diphasique à travers des fractures très rugueuses et étroites au sein d’une roche est davantage similaire à celui à travers un tuyau, plutôt qu’à travers des milieux poreux et des canaux à plaques parallèles.
Resumen
Para investigar los procesos de flujo de fluido bifásico influenciados por la interferencia de fases, la caída de presión, la rugosidad de la fractura y la tensión ambiental, se llevó a cabo un experimento de flujo bifásico de nitrógeno-agua en fracturas de granito altamente rugosas en una celda triaxial experimental. Se utilizó la presión para controlar el fluido bifásico en la fractura. Los resultados muestran que cada fase de fluido tiene un canal de flujo separado, incluso a través de fracturas de roca de alta rugosidad. La correlación de las velocidades superficiales de los fluidos bifásicos identifica el flujo anular con una alta caída de presión debido a la elevada energía cinética de la fase gaseosa. Sin embargo, el flujo anular pasó a ser un flujo complejo al aumentar la rugosidad de la fractura y la presión de confinamiento. La permeabilidad relativa del agua es mayor que la del gas. La suma de las permeabilidades relativas de las dos fases es inferior a la unidad debido a la interferencia de fases. Con el aumento de la carga hidráulica, la presión de confinamiento y la rugosidad de la fractura, la permeabilidad relativa del agua muestra una tendencia general a la baja y la suma de las permeabilidades relativas se reduce continuamente, lo que demuestra que las trayectorias de flujo localizadas de las diferentes fases cambian y la interferencia de fases aumenta. La permeabilidad relativa experimental del gas es mayor aquí que la determinada por el modelo de acoplamiento viscoso no lineal y el modelo Corey, pero menor que el modelo de permeabilidad relativa en línea recta (modelo X). Entre ellos, el modelo de acoplamiento viscoso es el que proporciona la mayor aproximación, lo que indica que el proceso físico del flujo bifásico a través de fracturas de roca altamente rugosas y compactas se asemeja más al que se produce a través de una tubería, en lugar de a través de medios porosos y canales de láminas paralelas.
摘要
为了研究相间干扰、压力降、裂隙粗糙度以及环境应力对岩体裂隙两相流体流动的影响, 利用三轴压力室开展了高粗糙度的花岗岩裂隙进行了氮气和水两相流体流动实验。两相流体的流动采用压力控制模式。研究发现, 在高粗糙度的花岗岩裂隙中, 每一相流体均具有独立的流动通道。两相流体表观流速分析显示:当压力降较大时, 两相流体具有环状流结构, 气体较高的动能是促使该流动模式的形成; 随着裂隙粗糙度以及围压的升高, 流动结构从环状流向混合流转变。整个实验过程中水的相对渗透率大于气体的相对渗透率, 并且由于相干涉, 两相的相对渗透率之和小于1。随着入口压力、围压以及裂隙粗糙度的增大, 水的相对渗透率总体呈下降趋势, 并且相对渗透率之和逐渐降低。这表明此时不同相流体的局部流动路径发生了变化, 相干扰增大。实验得到的气体相对渗透率高于粘滞耦合模型和Corey模型的预测值, 并且低于X模型, 但粘滞耦合模型得到的结果相对较为接近, 这说明两相流体通过高粗糙度致密岩石裂隙的物理过程更趋近于管道两相流, 而不是孔隙介质和平行板理想通道两相流。
Resumo
Para investigar processos de escoamento bifásico de fluido influenciados por interferência de fase, queda de pressão, rugosidade da fratura e estresse ambiental, um experimento de escoamento bifásico nitrogênio-água foi realizado em fraturas de granito altamente rugoso em uma célula triaxial experimental. A pressão foi usada para controlar o fluido bifásico na fratura. Os resultados mostram que cada fase do fluido possui um canal de escoamento separado, mesmo através de fraturas de rochas de grande rugosidade. A correlação das velocidades superficiais dos fluidos bifásicos identifica o escoamento anular com alta queda de pressão devido à alta energia cinética da fase gasosa. No entanto, o fluxo anular fez a transição para o fluxo complexo com o aumento da rugosidade da fratura e da pressão confinante. A permeabilidade relativa da água é maior que a do gás. A soma das permeabilidades relativas das duas fases é menor que a unidade devido à interferência de fase. Com o aumento da altura de pressão, pressão confinante e rugosidade da fratura, a permeabilidade relativa da água mostra uma tendência geral de diminuição e a soma da permeabilidade relativa continuamente reduzida, demonstrando que os caminhos de fluxo localizados das diferentes fases mudaram e a interferência de fase aumentou. A permeabilidade relativa experimental do gás é maior aqui do que aquela determinada pelo modelo de acoplamento viscoso não linear e modelo de Corey, mas menor do que o modelo de permeabilidade relativa em linha reta (modelo X). Entre eles, o modelo de acoplamento viscoso fornece a aproximação mais próxima, indicando que o processo físico do escoamento bifásico através de fraturas de rocha altamente rugosas e apertadas é mais parecido com um tubo, em vez de meios porosos e canais de placas paralelas.
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We are grateful for the constructive comments and suggestions of two anonymous reviewers and the associate editor, which helped to improve the manuscript.
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This study was financially supported by the National Natural Science Foundation of China (Grant Nos. 51674047 and 51911530152).
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Wang, Y., Zhang, Z., Ranjith, P.G. et al. Water-gas flow in rough rock fractures: insights from coupled triaxial compression experiments. Hydrogeol J 30, 1569–1581 (2022). https://doi.org/10.1007/s10040-022-02500-w
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DOI: https://doi.org/10.1007/s10040-022-02500-w