The development of hot dry rocks (HDRs) is of great significance to adjusting energy structure, alleviating energy shortage, reducing pollution, etc. Low-permeability granite is the predominant rock type in deep HDRs, making fractures the primary pathways for fluid circulation and heat extraction. The production of HDRs is significantly influenced by variable fracture conductivity, but current conductivity characterization primarily relies on the elastic deformation of the matrix, neglecting the impact of damage. Accordingly, we propose an experimental method and a supporting apparatus, which is used to unveil the conductivity evolution characteristics resulting from the comprehensive effects of damage and elastic deformation. The experimental results demonstrate that when subjected to confining force squeezing inward, the fracture conductivity experiences varying degrees of decrease compared to its initial state before the experiment. By utilizing the conductivity evolution rate as the evaluation criterion and conducting grey correlation analysis, it has been determined that temperature exerts the most significant influence on the conductivity evolution, followed by injection flow, and lastly, confining pressure. Moreover, rock particle types and production cycles also have different degrees of effect. After considering the comprehensive effects of damage-elastic deformation at the field-scale, the damage has a positive effect on conductivity enhancement. Our study provides a new approach for the characterization of fracture conductivity evolution for deep geothermal projects.

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Urban environmental governance is critical for responding climate change. Existing policies have been inefficient for addressing complicated socio-ecological issues. In order to further promote related studies, it is critical to have a comprehensive review so that recent research progresses can be summarized and future research directions can be identified. Under such a circumstance, this paper aims to conduct a bibliometric review on urban environmental governance, with a focus on addressing climate change. Based on 1697 articles published from 1997 to 2017 and searched from Web of Science, a systematic method combining bibliometric analysis and network analysis is applied to uncover the dynamic trends, academic collaboration and research hotspots. Results show that the overall publication quantity had been gradually improved. The key journals include Journal of Cleaner Production, Sustainability and Energy Policy. Authors from USA have the most publications and international co-authorships, followed by China and UK, while the most influential institution is the Chinese Academy of Science. Moreover, research keywords have been identified, including GHG emission, energy, water, health and transport. In terms of research methods, life cycle assessment and ecological footprint are the dominating methods. In order to further improve research in this field, it is crucial to combine different methods so that more innovative perspectives can be presented. Research findings from this study can also provide valuable policy insights to policy-makers so that appropriate urban environmental governance policies can be raised to mitigate the overall greenhouse gas emission.@en