Simplified storage barge and method of operation

A hydrocarbon storage system for storing liquid hydrocarbon, comprising:

• a longitudinally elongated barge hull (30) with bow and stern ends and with a tank assembly (57), where said tank assembly includes a plurality of tanks, said tank assembly including a first tank (C1S, C1C, C1P) at a first end of said hull and at least a second tank (C2S, C2C, C2P) lying adjacent to but longitudinally further from said first end of said hull than said first tank, with said first and second tanks having substantially coplanar tank bottom walls (130) and with a fluid coupling (72) that connects said first and second tanks, with said fluid coupling having a fluid coupling bottom lying at about the level of said tank bottom walls;
• a pump (44) coupled to said first tank for pumping out liquid hydrocarbon therefrom;
• said barge is devoid of an active seawater ballast system, and said barge has an inactive ballast system, that produces a predetermined orientation of said tank bottom walls so they are tilted by an angle (A) of at least 0.5° but no more than 8° from the horizontal when said tanks are empty, with the bottom wall of said first tank being lowermost.

A method for operating a hydrocarbon production system comprising a hydrocarbon production facility that includes at least one sea floor well, a storage barge that has a tank assembly, and an anchor system that anchors said vessel to the sea floor through a turret to allow said vessel to weathervane, so oil from said well can be stored in said tank assembly and offloaded from a major portion of said tank assembly to a tanker during offload periods spaced at least a week apart, comprising:

• transporting a temporary crew to said vessel when said tanker comes to said storage vessel, and using said crew to make connections and operate at least one pump to offload oil in said tank assembly to said tanker, and to later disconnect said connections and stop operations of said pump;
• removing said crew from said storage barge and sailing said tanker away from said storage barge, while allowing said storage vessel to remain without a crew for a period of at least a week while oil flows into tank assembly;
• allowing a passive ballast system to maintain said barge with said tank bottom walls tilted by 0.5° to 8° from the horizontal when said major portion of said tank assembly is less than 2% full, with a selected one of the bow and stern ends lowermost.