Gas production from heterogeneous hydrate-bearing sediments by depressurization in a large-scale simulator

Abstract

Large-scale simulation can improve the understanding of production behaviour from natural hydrate deposits, especially involving heterogeneous hydrates. In this work, a heterogeneous hydrate bearing sample formed from dissolved gas was depressurized in a 200 L simulator. Gas production along with fluid migration were investigated. 42.7% of the total methane gas in the reactor was produced, and water saturation in the sediment was only reduced from 0.66 to 0.56. Based on the results, gas production was divided into three stages, the second being intermittent gas production that resulted from interactions between the gas and water during hydrate dissociation. “Water invasion” and “water lock” interrupted the continuity of gas production and trapped a considerable portion of the released gas in the pores, which restricted active fluid migration into a narrow zone. The results also showed that sites with high hydrate saturation were weakly affected by water invasion, while those with low hydrate saturation were more vulnerable. In addition, a remarkable water lock effect was observed during depressurization at sites far from the production port.