Formation mechanism and geophysical properties of fracture-filling gas hydrate in the host sediments: A comprehensive review

Fracture-filling hydrate constitutes a pivotal component within the global hydrate reserves and serve as a significant focal point for hydrate exploration and development. However, the understanding of the formation mechanisms and geophysical properties of fracture-filling hydrate in sediments remains unclear. This review seeks to bridge this knowledge gap by comprehensively examining the formation mechanisms of fracture-filling hydrate from both micro-sedimentary and geological reservoir perspectives. It delves into various aspects of field tests, including seismic and logging, as well as laboratory tests covering acoustic properties, permeability, thermal properties, electrical resistivity, and mechanical properties. It aims to shed light on the challenges associated with the characteristics of fracture-filling hydrate reservoirs and their geophysical properties while proposing potential solutions, and emphasizes the urgency of identifying the formation patterns of fracture-filling hydrate and estimating resource volumes. Furthermore, the review emphasizes the importance of collaborative geophysical characterization testing for fracture-filling hydrate as a crucial step in addressing this challenge. It advocates for fostering international cooperation for global data integration and sharing as a viable solution to advance our understanding and management of these valuable resources.