Sand production behaviors of the wellbore zones in gas hydrate-bearing reservoir: Insights from meter-scale visualization experiments

Sand production is one of the bottlenecks hindering the long-term， safe， and efficient production of natural gas hydrate (NGH). Visualizing the sand production processes is essential for understanding their dynamic response and managing the associated risks. Yet， existing visualization experiments on sand production in gas hydrate-bearing sediments (GHBSs) are typically confined to small scales， often at or below the decimeter level， where boundary and size effects can compromise the accuracy of predictions. Herein， we used a meter-scale visualization experimental system to simulate the sand production process around the wellbore zone in GHBSs. The interconnections between macroscopic sand production patterns， sand production mass， and fluid pressure were clarified under two critical factors of production rate and medium. The results show that sand production manifests as four successive patterns: wormholes， collective invasion， creeping advancement， and erosion channels， governed by both the production rate and fluid medium. The coexistence of high gas production rates and free water content raises sand production risks， whereas a gas-rich environment reduces them. Fluid pressure changes can reflect sand production-induced structure damage. Sand production patterns like collective invasion have minimal impact， while significant formation structural damage， such as erosion channels and numerous wormholes， can cause a notable decline in fluid pressure. This study provides valuable insights for understanding sand production behavior， advancing sand production simulations based on continuum-medium theory， and guiding hydrate production and sand control in field applications.