Experimental study of dual-well gas injection and brine discharge in salt cavern sediment space

Docking Well underground salt cavern storage (DWUSCS) is a novel construction method that enables dual-well to be used for gas injection and brine discharge (GIBD), resulting in improved efficiency, cost savings, and greater utilization of the cavity space. However, the uncertainties of insoluble materials and the discharge patterns have retarded the research status in dual-well GIBD studies. In this study, we analyzed the insoluble materials of the DWUSCS layer, and investigated the factors that affect sediment space injection and discharge in the connecting channel through GIBD simulation experiments. We found that the densities of insoluble mineral components were similar to those of rock salt. Our simulation experiments revealed that the greater the permeability of the sediment space, the larger the void fraction, the more micron-sized particles in the insoluble materials, and the more brine that can be discharged during GIBD. During OIOD, gas injection pressure rises rapidly and then stabilizes before gas discharge. When the gas is discharged with brine, the pressure drops dramatically and finally reaches equilibrium. The gas injection flow rate has an impact on the discharge of brine, flow rate with 10 mL/min can displace more brine than 100 mL/min. The angle of the connecting channel also influences the effect of brine discharge in the sediment space during OIOD. Specifically, when the angle of the channel is 0°, the discharge volume is minimum, but it increases with increasing angle, and the optimal angle relates to permeability. In the case of a horizontal connecting channel, TIOD (the discharge outlet is at the bottom of the channel) (TIOD (bottom)) can discharge the maximum amount of brine. For large GIBD device, TIOD (bottom) will expend more than 50 times experimental periods than OIOD. By using OIOD first and then TIOD (bottom), the construction period can be shortened and the economic cost reduced. These findings provide valuable insights into the GIBD process from on-site DWUSCS.