Fine sand migration in hydrate-bearing sediments and median grain size ratio optimization of gravel pack

Sand production greatly influences reservoir stability and safety during gas hydrate exploitation in hydratebearing sediments (HBS). Gravel packing is an effective method for sand control. Median grain size ratio (D-50/d(50)) values and sand migration of gravel pack are important factors in sand control during gas hydrate exploitation. This paper focuses on sand migration in samples with an optimal (D-50/d(50)) value during the hydrate dissociation process. Four samples with different D-50/d(50) values were tested to obtain the optimal D-50/d(50) for gas hydrate exploitation. Then, a sand migration experiment was conducted on the sand sample with the optimal D-50/d(50) with X-ray computed tomography (CT) to obtain the sand migration during the hydrate dissociation process. The results showed that 6.5 was the optimal D-50/d(50) value for the selection of the gravel median grain size. The occurrence of sand-bridge structures in the pore space of the sample (D-50/d(50) = 6.5) was a significant phenomenon during hydrate dissociation and were beneficial to both gas production and sand control. Free sand migrated in the pore space of the mixed sample (D-50/d(50) = 6.5) and formed sand-bridge structures due to hydrate dissociation. The formation and destruction of trapped gas structures were mainly influenced by sand-bridge structures caused by sand migration. The results in this paper could provide useful insight into sand production behaviors induced by sustainable gas production in HBS.

Automated summary

This study explores the importance of gravel packing for sand control during gas hydrate exploitation, finding that a D-50/d(50) value of 6.5 is optimal. The formation of sand-bridge structures at this value contributes positively to gas production and sand control in hydrate-bearing sediments.