Investigating petrophysical properties of gas hydrate-bearing sediments using digital rock technology: A microscopic perspective

Natural gas hydrates are crystalline solid complexes with different morphologies found in marine sediments and permafrost zones. The petrophysical properties of gas hydrate-bearing sediments (GHBS) are crucial for understanding the characteristics of gas hydrate reservoirs, the spatial distribution of natural gas hydrates, and their exploitation potential. Geophysical exploration remains the primary approach for investigating the petrophysical properties of GHBS. However, limitations in resolution make it challenging to accurately characterize complex sediment structures, leading to difficulties in precisely interpreting petrophysical properties. Laboratory-based petrophysical experiments provide highly accurate results for petrophysical properties. Despite their accuracy, these experiments are costly, and difficulties in controlling variables may introduce uncertainties into geophysical exploration models. Advances in imaging and simulation techniques have established digital rock technology as an indispensable tool for enhancing petrophysical experimentation. This technology offers a novel microscopic perspective for elucidating the three-dimensional (3D) spatial distribution and multi-physical responses of GHBS. This paper presents an in-depth discussion of digital rock technology as applied to GHBS, with an emphasis on digital rock reconstruction and simulation of petrophysical properties. First, we summarize two common methods for constructing digital rocks of GHBS: petrophysical experimental methods and numerical reconstruction methods, followed by analyses of their respective advantages and limitations. Next, we delve into numerical simulation methods for evaluating GHBS petrophysical properties, including electrical, elastic, and fluid flow characteristics. Finally, we conduct a comprehensive analysis of the current trends in digital rock reconstruction and petrophysical simulation techniques for GHBS, emphasizing the necessity of multi-scale, multi-component, high-resolution 3D digital rock models to facilitate the precise characterization of complex gas hydrate reservoirs. Future applications of microscopic digital rock technology should be integrated with macroscopic geophysical exploration to enable more comprehensive and precise analyses of GHBS petrophysical properties.