Abstract: A riser system for transporting slurry from the seabed to the sea surface. The riser system comprises a first and second riser, a slurry pump system (17) to transport slurry up one of the risers, and a waste water pump system (107) to return waste water down one of the risers. The slurry pump system and the waste water pump system are selectively connectable to each of the risers to allow each riser to be either a slurry riser (1) or a waste water riser (2). With this arrangement, if a slurry riser develops a leak partway along its length the waste water riser can be converted into a slurry riser such that operation can continue.

Abstract: A suction mouth (10) for mounting on the front of a subsea mining tool and to be pushed into sediment. The suction mouth comprises a hollow body (12) having an entrance opening (14) and an exit opening (16), wherein the body converges from the entrance opening towards the exit opening. The entrance opening has a lower lip (20) and an upper lip (22), and the upper lip comprises an extension (22a) projecting forwardly and upwardly relative to the lower lip to form a canopy over the entrance opening. The suction mouth (10) may include a valve (30) on the body downstream of the entrance opening which is operable to selectively provide a further entrance opening into the body. Where such a valve is present, the consistency of the material sucked in can be regulated.

Abstract: A method and apparatus for mining and processing seabed sediment comprising disturbing sediment at the seabed (3) to form a slurry; transporting the slurry to the surface via a production riser (6) and processing the slurry to dissociate hydrates and remove hydrates from the slurry in gaseous form at the surface. The slurry may also contain sapropel and minerals. If so, the slurry may be split into a mineral rich stream and a sapropel rich stream each of which may be subjected to further treatment.

Abstract: A riser system for transporting slurry from the seabed to the sea surface. The riser system comprises a first and second riser, a slurry pump system (17) to transport slurry up one of the risers, and a waste water pump system (107) to return waste water down one of the risers. The slurry pump system and the waste water pump system are selectively connectable to each of the risers to allow each riser to be either a slurry riser (1) or a waste water riser (2). With this arrangement, if a slurry riser develops a leak partway along its length the waste water riser can be converted into a slurry riser such that operation can continue.

Abstract: A suction mouth (10) for mounting on the front of a subsea mining tool and to be pushed into sediment. The suction mouth comprises a hollow body (12) having an entrance opening (14) and an exit opening (16), wherein the body converges from the entrance opening towards the exit opening. The entrance opening has a lower lip (20) and an upper lip (22), and the upper lip comprises an extension (22a) projecting forwardly and upwardly relative to the lower lip to form a canopy over the entrance opening. The suction mouth (10) may include a valve (30) on the body downstream of the entrance opening which is operable to selectively provide a further entrance opening into the body. Where such a valve is present, the consistency of the material sucked in can be regulated.

Abstract: A method of recovering a deposit from the sea bed using a surface vessel (20) untethered from the sea bed and first and second suction vehicles (27; 30) which traverse the sea bed to suck up the deposit and are each connected to the surface vessel by a respective flexible riser (26; 29) along which a slurry of the deposit is transferred from the suction vehicles to the surface vessel. The method comprises moving the first and second suction vehicles to and fro across the sea bed in a plurality of lanes such that they travel substantially further than the surface vessel, turning or reversing each vehicle at the end of each lane in a manner such that the lanes are adjacent to one another to mine the deposit substantially without gaps between adjacent lanes. Only the suction vessels rest on the sea bed.

Abstract: A method and apparatus for mining and processing seabed sediment comprising disturbing sediment at the seabed (3) to form a slurry; transporting the slurry to the surface via a production riser (6) and processing the slurry to dissociate hydrates and remove hydrates from the slurry in gaseous form at the surface. The slurry may also contain sapropel and minerals. If so, the slurry may be split into a mineral rich stream and a sapropel rich stream each of which may be subjected to further treatment.