Permeability of Hydrate-Bearing Sediments and Its Influencing Factors Using the Pressure Oscillation Testing Method

The permeability of natural gas hydrate-bearing sediments is a key physical parameter constraining their commercial development. Current research predominantly focuses on measuring permeability in sediments with varying hydrate saturations using steady-state and transient pressure pulse methods, whereas the applicability of the periodic pressure oscillation method for measuring hydrate-bearing sediments remains inconclusive. Furthermore, studies investigating the effects of clay content and effective confining pressure on hydrate-bearing sediment permeability remain limited. To address this gap, this study designed a periodic pressure oscillation method for permeability measurement across different hydrate saturations and evaluated its applicability in hydrate-bearing sediments based on transient pressure pulse measurements, model predictions, and existing literatures. Subsequently, this method was employed to systematically investigate the influence of clay content and effective confining pressure on sediment permeability. By integrating pressure response characteristics, permeability variation trends, and pore structure evolution mechanisms, the effects of clay content and effective confining pressure on seepage behavior in hydrate-bearing sediments were elucidated. The results demonstrate that the periodic pressure oscillation method not only accurately characterizes the permeability of hydrate-bearing sediments but also aligns well with the trends predicted by established permeability models, confirming its strong applicability for such measurements. Furthermore, in ultralow-permeability systems, the periodic pressure oscillation method can effectively avoid problems such as slow pressure decay, prolonged test duration, and cumulative data errors in the steady-state and transient pressure pulse methods. Sediment permeability gradually decreases with increasing clay content, and the proposed model Kc effectively characterizes the seepage behavior of sediments under the combined effects of clay content and hydrate saturation. Sediments permeability exhibits a significant linear decrease with increasing effective confining pressure. Specifically, for every 1 MPa increase in effective confining pressure, permeability declines by approximately 23%. Additionally, as clay content increases, the sensitivity of sediment permeability to effective confining pressure diminishes progressively.