Breakthrough Pressure Testing of Subsea Hydrate-Bearing Caps: Methods, Limitations, and Future Perspectives

The safe production of natural gas in reservoir highly depends upon sealing capacity of the conventional and hydrate-bearing caps, with breakthrough pressure serving as the primary evaluation indicator. This study first systematically summarizes the basic principles, procedures, and applicable conditions of five traditional and auxiliary methods for testing conventional caps, namely mercury intrusion porosimetry, the pulse method, the stepwise pressurization method, the continuous injection method, and the displacement method. Building on this foundational understanding, the study then delves into an in-depth analysis of the limitations inherent to these methods when they are applied to hydrate-bearing caps, as well as potential strategies for their improvement. Upon thorough comparative analysis, this study highlights that the stepwise pressurization method, continuous pressurization method, and the pulse method are the potential techniques for determining the breakthrough pressure measurement of hydrate-bearing caps, provided that improvements are made in specimen preparation, temperature-pressure and stress state control. The suitability of these methods depends upon factors such as hydrate saturation and experimental conditions. Finally, this review summarizes current research progress and key challenges in this field. It is proposed that the development of full-process in-situ pressure-core testing systems, the establishment of unified criteria for breakthrough and loading path, and studies on cyclic breakthrough self-healing behavior are crucial steps for transitioning this research from laboratory settings to practical engineering applications.