Experimental Investigation into Dissociation Characteristics of Methane Hydrate in Sediments with Different Contents of Montmorillonite Clay.

Abstract

The characteristics of gas production in sediments are crucial to the safe and efficient exploitation of gas hydrate resources. However, research on methane hydrate dissociation in these sediments, particularly in silty-clayey sediments, which are commonly found in nature, remains limited and contains significant gaps. To address this, a series of depressurization experiments were conducted to investigate the dissociation behavior of methane hydrate in silty-clayey sediments with montmorillonite contents ranging from 0 to 20 wt %. The results indicate that montmorillonite significantly inhibits methane hydrate dissociation. When the montmorillonite content increases from 10 to 20 wt %, the average dissociation rate of methane hydrate decreases by approximately 47%-78% compared to sandy sediments. An excess temperature drop of around 0.13 to 0.40 K was observed in the depressurization process as the montmorillonite content increased from 10 to 20 wt %. Methane hydrate dissociates unevenly in montmorillonite clay-bearing sediments due to the nonuniform distribution of the methane hydrate, coupled with the low thermal conductivity and high-water absorption capacity of montmorillonite, which restrict the supply of extra heat. The electrical resistance changes further reveal that the increased bound water content in clayey sediments reduces the impact of water fluctuation on the resistivity changes. Consequently, the resistivity changes in sandy sediments are more pronounced compared to silty-clayey sediments. These findings provide valuable insights for optimizing methane hydrate production technology via depressurization.