Underwater gas field development methods and systems

An underwater gas pressurization unit comprising:

• at least one vessel arranged to receive gas through a top of the vessel and seawater through a bottom of the vessel, the at least one vessel further comprising a layer of water-immiscible liquid separating between the gas and the seawater, wherein the water-immiscible liquid is selected to have a density which is intermediate between a density of the gas and a density of the seawater;
• and
• a valve system arranged to pressurize the gas by, repeatedly, introducing the seawater into the vessel, evacuating the pressurized gas through the top of the vessel upon reaching a specified pressure and introducing gas into the vessel by evacuating the seawater through the bottom of the vessel,
• wherein the underwater gas pressurization unit is configured to pressurize the gas continuously by the repeating of the seawater introduction, the pressurized gas evacuation, the gas introduction and the seawater evacuation,
• wherein the water-immiscible liquid comprises aliphatic or aromatic organic compounds or their mixtures, has a density smaller than seawater and has a freezing temperature below −20° C., and
• wherein the water-immiscible liquid is selected from:
• hexane, hexane isomers, heptane, heptane isomers, toluene, derivatives thereof and mixtures thereof,
• wherein the at least one vessel comprises at least one pair of vessels, in each of the at least one pair, the two paired vessels operate reciprocally—one of the vessels pressurizing gas while the other one of the vessels receiving gas.