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Главная SOME ENGINEERING APPROACHES TO FISH PROTECTIVE MEASURES
SOME ENGINEERING APPROACHES TO FISH PROTECTIVE MEASURES Печать E-mail

GARBARENKO O.K., KAPLIN I.V.
OJSC «CDB «Corall», Ukraine

Construction Rules and Regulations (SNiP) 2.06.07-87 «Retaining Walls, Navigation Locks, Fish Passage/Protective Structures» require that water intake works operating in bodies of water (water basins) should be provided with fish protective facilities. It should be noted that according to The Water Code of Russian Federation by a body of water is meant «a water accumulation so structured on either the surface of land in its relief forms or in land entrails as having bounds, space and features of water regime», which excludes seas from this definition, for example, inactive floating installations are not required to have a fish protective device (FPD) fitted to a water scoop. However, the Governmental environmental expertise authorities of Russian Federation call for providing water scoops of exploratory offshore drilling rigs and oil/gas production offshore platforms with FPDs.

Standard proven engineering approaches to offshore installations are not available at present, which is borne out by the patent search in lead oil/gas producing states. It should be pointed out that the laws of lead oil producing countries do not include any mandatory provisions for fitting out FPDs on the scoop inlets of offshore installations. It is apparent that in sea conditions the water consumption is relatively low as compared to agricultural or, for instance, urban needs in water taken from inner water bodies and rivers. Damage adversely affected to sea-water fish stocks through the water consumption by offshore drilling and oil/gas producing units is relatively insignificant. It should be recognized that offshore platforms are built according to the Rules for the Classification and Construction of Sea-Going Ships of the Russian Maritime Register of Shipping (RMRS). From this it follows that all water inlets should be RMRS-approved. By this is meant that any FPD designs should have a RMRS certificate.

Of all the mechanical water scoops providing effective protection of young fish in way of water intake works on offshore oil producing installations Main Federal Office of Fishing Economic Expertise and Standards on Fish Stock Protection, Reproduction and Acclimatization (FGU «TCHUREN») recommended devices of three types fabricated and tested by Osanna Company in Engels (Russia).

One of the problems associated with the use of mechanical FPDs is their frequent maintenance. The practice of contacts with FPD designers and producers showed that those could not guarantee at least half-yearly operation of the devices in question without cleaning.

In addition the mechanical FPDs require that these should be provided with a system capable of monitoring the effectiveness of their operation, i. e. appropriate sensors should be mounted inside the FPDs. Accordingly this involves underwater installation of special cables, with cable entries being water-proof.

FGU «TCHUREN» recommends applying:
• ARS fish protective drum,
• hydrodynamic head,
• cone-shaped net incorporating a fish diverting device.

Louver-type FPDs are also known. These have the advantages that any rotating components are not available, however there are no data proving their protective efficiency required by SNiP 2.06.07-87.

Alternatively, there can be applicable mechanical FPDs based on electrical field scare effect.
The above method is more effective as it provides not only the protection of young fish, but fish larva as well, with it having no harmful effect on the ichthyofauna.

Research/Production Company Gradient in Donetsk (Ukraine) has developed an environmentally friendly electro gradient method for protecting fish (EGFP), including young ones, against becoming trapped in any water intake structures. This method has been implemented in some Russian and Ukrainian large water intake facilities. The above method is based on fish scaring effect by inducing an electromagnetic field having particular parameters over the entire cross section of a water intake channel. At present time the EGFP method has been implemented in various types of fresh water intake facilities.

The EGFP devices were subjected to 2-year ichthyologic tests performed by experts of Governmental Fish Inspection on different water intake structures. Their operating efficiency turned out to be in the range of 76 to 90%.

Both technologically and economically this method is more beneficial. At the same time the EGRP experience of operation in offshore environment and on metallic installations is lacking. The latter point relates to some concerns stated in publications that structural steelwork may be subjected to intensive corrosion under effect of electromagnetic fields in sea water.

One of the new products is a physiology-type FPD developed for the Obskaya submersible drilling unit intended for exploratory drilling in the Ob mouth and Pechora Sea. It is a fish protection leaf filter built in the water inlet window and provided with oscillating plates. Such a FPD was developed by Research/Production Center Akvos in Engels (Russia). The design documentation to the device of this type was approved by Federal Service of Veterinary and Phitosanitary Supervision.

Each of the FPDs intended for offshore installations is a unique design to be developed by a specialist company using materials immune to aggressive marine environment and duly tested as a pilot specimen for providing 70-% efficiency as required by SNiP. As for tests, special catchers are to be so constructed that these can be fitted to the water inlets downstream the FPD for the purpose of controlling young fish entrapment by the inlets having and not having FPDs. In regard to ice-resistant platforms, the tests involve, besides the catchers, diving works for installation and removal of these catchers and check fish counts within a short iceless period, which, apart from the above mentioned problems, also restricts shipboard operations.

As evident from the above SNiP, a fish protection device should be provided with rotating and close-meshed net-shaped parts. While in the aggressive marine environment, the rotating parts need to be lubricated and maintained, with plankton, fouling and fine refuse removed from the nets. It is expected that permanent access should be ensured for maintenance, which can be established by applying three approaches:
• underwater maintenance,
• FPD periodical recovery on deck for maintenance, and
• installation of the FPD inside the platform with provision of access to it.

In the case of the first and second approaches, the FPD is supposedly to be fitted to the external surface of the platform underwater part. However, the site of ice-resistant platforms is characteristic by prolonged and complicated ice situation, and it is therefore a higher probability of ice impact on the hull underwater structures. In this connection the access of divers for periodic and emergency maintenance will be restricted during lengthy period of time. It should be also taken into account that said platforms are not staffed with a regular team of divers and not equipped with all necessary diving equipment. It follows that it takes substantial time and cost to organize and bring the diving team by ship to a platform site.

From the point of view of maintenance convenience, the FPD recovery on deck, at first sight, appears to be the most acceptable one. In this case it is assumed that guides, automatic disconnectors, special clamps and lifts should be provided to ensure the FPD maintenance. In this case some problems occur because cables will have to be installed to operate FPD sensors. Cable installation on the hull underwater part must ensure the FPD retrieval without using complicated underwater electrical connectors. And once again, ice and its probable impact on the similar structures, which are supposed to be arranged outside the underwater part of the platform hull, exclude the application of above structures, otherwise a risk to damage may happen.

Damage to or clogging of the water scoops is not tolerable because in this case the emergency firefighting system will be out of operation, which directly threatens the personnel life and may cause a serious environmental disaster. It is worthy of note that the oil/gas production platform are hazardous production installations which higher safety requirements are imposed upon.

Thus the position of the fish protection device on the outside underwater surface of the platform also involves difficulties.

As for the location of the fish protective device inside the platform, our experience of designing the Caspian submersible drilling unit says that this version requires spacious rooms, with these being adjacent to the platform external hull part on one side and placed just downstream the inlets so that a fish diverting device can be constructed beyond the water scoop (for structures having a cone shaped net). It should be remarked as well that, on the basis of our experience, the regular maintenance of these structures (frequent cleaning of the net-shaped cone stipulated by the FPD designers in the Operating Manual) by regular installation personnel is a challenge to the installation operator, which is especially problematic because limited regular personnel is available on board platforms.

Thus, only a minor experience of engineering approaches to fish protective measures exists at present, with future efforts demanded for finding adequate answers to the questions as put above.

OIL AND GAS OF ARCTIC SHELF 2008 

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