Gas hydrate reservoir quality enhanced by framboidal pyrite formation

Gas hydrate enrichment mechanisms and reservoir characteristics are crucial for understanding their resource potential and role in the global carbon cycle. Traditional models emphasize coarse-grained sediments as primary hosts for hydrates, but recent studies show significant accumulations also occur in fine-grained systems. However, the influence of authigenic minerals, particularly porous framboidal pyrite, on reservoir properties in such settings remains poorly understood. This study examines framboidal pyrite from three gas hydrate drillsites in the northern South China Sea: GMGS4-SC-W02B and GMGS4-SC-W03B in the Pearl River Mouth Basin, and GMGS2–16 in the Taixinan Basin. Integrated sedimentological, mineralogical, and petrophysical analyses, including scanning electron microscopy (SEM) and micro-computed tomography (micro-CT), show that framboidal pyrite aggregates exhibit substantial porosity (ranging from 8.1% to 80.2%) and well-connected pore networks that enhance sediment permeability and provide favorable storage space for gas hydrates. Key controlling factors include framboid size, microcrystal morphology, and size, all of which are influenced by geochemical conditions associated with anaerobic oxidation of methane (AOM). Additionally, pyrite microcrystals promote hydrate nucleation through their high specific surface area, defect-rich surfaces, and hydrophilic interactions, which enhance methane adsorption and facilitate heterogeneous crystallization. These findings demonstrate that framboidal pyrite actively facilitates hydrate storage and precipitation, rather than being a passive diagenetic product influenced solely by methane flux from hydrate dissociation, offering a refined geological framework for resource assessment and predictive exploration in fine-grained hydrate systems globally.