Effect of Confining Pressure on Unconsolidated Quartz Sand Under Conditions Relevant to Gas Hydrate Reservoir Modeling

Gas hydrate accumulations are often hosted in loose and weakly cemented sandy sediments, where hydrate dissociation weakens its cementing effect on the granular skeleton. Under these conditions, flow behavior may depend not only on the release of pore space but also on subsequent mechanical rearrangement of the sand matrix. The aim of this study was to evaluate the effects of external confinement and loading history on the pore space and flow response of unconsolidated quartz sand. Experiments were conducted on an extended sand-pack model enclosed in an elastic sleeve and subjected to hydraulic confinement, with distributed measurements of pressure, temperature, and electrical resistance; grain morphology was examined by scanning electron microscopy. The quartz grains exhibited pronounced angularity and heterogeneous surface microrelief. During three successive loading cycles to 190 kPa, pore volume decreased nonlinearly, and hysteresis was observed between the loading and unloading branches. The strongest spatial differences in electrical response occurred during the first cycle, whereas repeated loading reduced the differences among individual sections. Without external confinement, changes in flow regime were accompanied by marked changes in relative electrical resistance; after preliminary cyclic loading and at a confining pressure of 190 kPa, this effect was substantially weaker in most monitored sections. The results indicate that physical modeling of unconsolidated gas hydrate reservoirs should account for external pressure and the loading history of the granular medium, together with pore-space and flow characteristics. Because the two flow-test states differed simultaneously in current confinement and prior loading history, their contrast is interpreted as a combined mechanical-state effect rather than as an isolated effect of confining pressure.