Retention device for retained substance and retention method

A retention method for retaining a retained substance including at least one from carbon dioxide, a substance having larger solubility to water than carbon dioxide, and methane under the ground, comprising:

• using a retention device for retaining the retained substance comprising an infusion well reaching to a saltwater aquifer, a pump device pumping the retained substance to the infusion well, and a porous member made of ceramics and placed in the infusion well;
• forming a horizontal well toward a substantially horizontal direction in at least one part of the infusion well in the saltwater aquifer;
• generating microbubbles of the retained substance when the retained substance is infused through the porous member to the saltwater aquifer;
• and
• making the microbubbles descend in the saltwater aquifer,
• wherein the porous member (i) is provided in a lower part of the horizontal well, (ii) is formed by mixing particles made of ceramics and binder, and (iii) has a mode of aperture distribution is distribution of 4.5 micrometers or less, and
• wherein a ring member fixed in the horizontal well comprises:
• an upper part composed of metal;
• and
• a lower part that (i) is mounted to the upper part and (ii) carries the porous member between an inner surface of the ring member facing an interior of the horizontal well and an outer surface of the ring member opposite the inner surface.