Large scale experimental evaluation to methane hydrate dissociation below quadruple point in sandy sediment

The Pilot-Scale Hydrate Simulator (PHS), a three-dimensional 117.8 L pressure vessel, is applied to study the methane hydrate dissociation below the quadruple point in the sandy sediment in this work. The hydrate dissociation behaviors below and above the quadruple point are compared. The influences of the production pressure, the initial reservoir temperature, and the water saturation on the hydrate dissociation below the quadruple point by depressurization are investigated. The results indicate that methane hydrate dissociation below the quadruple point causes ice formation, which can strongly enhance the dissociation rate of the hydrate. The water generated from hydrate dissociation below the quadruple point may immediately form ice and the pore water in the reservoir turns into ice at the same time. Meanwhile, the hydrate dissociation below the quadruple point consumes the latent heat released by ice formation. The lower production pressure causes the higher driving force for hydrate dissociation and ice formation, which results in the higher dissociation rate of the hydrate. In addition, when the production pressure is lower than the quadruple point, a lower initial reservoir temperature is favorable for ice formation, which leads to the higher hydrate dissociation rate. The experimental results from hydrate dissociation in the 'water-saturated' reservoir and 'gas-saturated' reservoir indicate that the rate of ice formation is slower in the 'water-saturated' reservoir.