Hydrate dissociation induced by depressurization in conjunction with warm brine stimulation in cubic hydrate simulator with silica sand

Abstract

To study the effect of salt concentration of brine injection on hydrate dissociation, hydrate dissociation experiments induced by depressurization in conjunction with warm brine stimulation have been carried out in a Cubic Hydrate Simulator (CHS). The dual horizontal wells were set as the well configuration. The results indicate that the salinity in the reservoir decreases continuously during the depressurizing stage under the mixture of fresh water from hydrate dissociation. However, the salinity increases overtime during the constant-pressure stage (the injection stage) by the mass transfer with the injected brine. The gas production rate and heat-transfer rate for pure water injection are lower than those for brine injection. In addition, raising the injected salinity can enhance the rates of heat transfer and gas production when the salinity is lower than 10.0%. However, the promotion effect of brine injection on hydrate dissociation is limited when the injected salinity is beyond 10.0%. This is because the specific heat of the brine declines with the increase of the salinity, which causes the decrease of heat injection rate. The water production rate equals to the water injection rate in the process of brine injection. The energy analysis and the evaluation of energy ratio indicate that the optimal injected salinity in this work is 10.0%.