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

Abstract

Sand production greatly influences reservoir stability and safety during gas hydrate exploitation in hydrate-bearing sediments (HBS). Gravel packing is an effective method for sand control. Median grain size ratio (D50/d50) 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 (D50/d50) value during the hydrate dissociation process. Four samples with different D50/d50 values were tested to obtain the optimal D50/d50 for gas hydrate exploitation. Then, a sand migration experiment was conducted on the sand sample with the optimal D50/d50 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 D50/d50 value for the selection of the gravel median grain size. The occurrence of sand-bridge structures in the pore space of the sample (D50/d50 = 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 (D50/d50 = 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.