Apparatus and methods for cleaning an ocean bottom cable
A cleaning apparatus ( 100 ) for an ocean bottom cable ( 19 ) including a plurality of node casings ( 5 ), each containing at least one sensor capsule ( 9 ). During retrieval, an initial flushing device flushes the assembled cable with seawater before the capsules ( 9 ) are separated from the casings ( 5 ) in a loading/unloading apparatus ( 300 ). A washing tunnel ( 110 ) is configured to flush the sensor capsule ( 9 ) with water supplied from a freshwater tank ( 115 ) through a waterfeed pipe ( 117 ). Preferably, the cleaning apparatus also comprises a secondary flushing device for flushing the components with seawater after separation, and a drying tunnel ( 120 ). Separate conveyors convey the sensor capsules ( 9 ) and the node casings ( 5 ) to their respective destinations, such that each component may be flushed in seawater and/or freshwater and/or dried as required. The cleaning apparatus is optimized to use a minimum of freshwater and energy.
1. A cleaning apparatus for an ocean bottom cable including a plurality of node casings interconnected by stress elements comprising:
an initial flushing device configured to flush the ocean bottom cable with seawater;
a loading/unloading apparatus disposed downstream from the initial flushing device, wherein the loading/unloading apparatus is configured to unload a sensor capsule from a node casing during retrieval of the ocean bottom cable to a seismic survey vessel;
a washing tunnel disposed downstream from the loading/unloading apparatus, wherein the washing tunnel is configured to flush the sensor capsule with water supplied from a freshwater tank through a waterfeed pipe and water nozzles;
first conveyor means configured to convey the sensor capsule from the unloading apparatus to a service station during said retrieval and in an opposite direction during a deployment; and
second conveyor means configured to convey the stress elements and node casings from the loading/unloading apparatus to a storage reel during said retrieval and in the opposite direction during the deployment.
2. The cleaning apparatus according to claim 1 , wherein the first conveyor means are disposed within the washing tunnel.
3. The cleaning apparatus according to claim 1 , wherein the second conveyor means are disposed within the washing tunnel.
4. The cleaning apparatus according to claim 1 , wherein the first conveyor means pass a secondary flushing device configured to flush the sensor capsule with seawater.
5. The cleaning apparatus according to claim 1 , wherein the second conveyor means pass a secondary flushing device configured to flush the node casing with seawater.
6. The cleaning apparatus according to claim 1 , further comprising a drying tunnel disposed downstream from the washing tunnel, wherein the drying tunnel comprises gas nozzles fed from an accumulator.
7. The cleaning apparatus according to claim 6 , wherein the first conveyor means are disposed within the drying tunnel.
8. The cleaning apparatus according to claim 6 , wherein the second conveyor means are disposed within the drying tunnel.
9. The cleaning apparatus according to claim 6 , further comprising a stacking device configured to stack the sensor capsules in a rectangular cassette with the longitudinal axes of the sensor capsules perpendicular to the rectangular plane spanned by the sides of the cassette.
10. The cleaning apparatus according to claim 9 , wherein the stacking device is arranged between the loading/unloading apparatus and the washing tunnel.
11. The cleaning apparatus according to claim 1 , further comprising a drain pipe extending from the bottom of the washing tunnel to a discharge pipe extending to a region outboard of the seismic survey vessel.
12. The cleaning apparatus according to claim 11 , further comprising a supply pipe extending from the drain pipe to the waterfeed pipe; and a control module configured to operate valves to discharge wastewater through the discharge pipe and replace the discharged wastewater with freshwater from the freshwater tank whenever the salinity in the wastewater in the drain pipe exceeds a predetermined threshold value.
13. The cleaning apparatus according to claim 1 , further comprising a water heater on the waterfeed pipe.
14. The cleaning apparatus according to claim 13 , wherein the water heater comprises a heat exchanger configured to convey heat from wastewater to the water supplied to the water nozzles.
15. The cleaning apparatus according to claim 1 , further comprising a gas heater on a gasfeed pipe comprising the gas nozzles.
16. The cleaning apparatus according to claim 15 , wherein the gas heater comprises a heat exchanger configured to convey heat from wastewater to the gas supplied to the gas nozzles.
17. A method for cleaning an ocean bottom cable including a plurality of node casings interconnected by stress elements, each node casing comprising at least one sensor capsule, the method comprising the step of conveying the sensor capsules and the ocean bottom cable through a cleaning apparatus of claim 1 either both in a downstream direction or both in an opposite direction.
18. The method according to claim 17 , further comprising a step of applying an anti-fouling agent to the ocean bottom cable and/or the sensor capsules.