Experimental Investigation of Characteristics of Sand Production in Wellbore during Hydrate Exploitation by the Depressurization Method

Sand production is the process in which formation sand and gravel would migrate into the wellbore by the flow of reservoir fluids. This is a significant problem that endangers the safety of hydrate exploitation. The aim of this study is to understand sand production during hydrate exploitation. A novel experimental apparatus was constructed to examine sand production in the hydrate layer by using the depressurization method. Hydrate production was divided into three periods: water, gas with water drops, and gas. We detected sand production in the first two periods: fine sand in the first period and sand grains in the second. The temperature related characteristics of the hydrate layers and the rates of sand production differed during different stages of hydrate production. The unique sputtering occurring owing to the decomposition of the hydrate might have provided the driving force for sand migration, and water gas bubbles or gaseous water drops from the decomposed hydrate might have enhanced sand carrying capacity. The subsidence of hydrate-bearing sediments was influenced by sand production, whereas the maintenance of crustal stress possibly influenced the rate and magnitude of subsidence. Future experimental and numerical research into the dynamical thermal properties and material balance of the hydrate layer production must consider its dynamic subsidence.