| The disposition of the decommissioning offshore oil platform and related facilities hasbecome one of the most critical environmental issues that draw attention all over the worldin recent years. Transforming the decommissioning offshore oil production facilities intoartificial reefs can not only save the cost of demolition, but also reduce the risk of offshoreoperation and minimize the influence to marine ecological environment. So it has importanteconomic, social and environmental significance.In this paper, Chengdao oilfield was taken as the research object. Based on theinvestigation of the regional environmental situation, the main researches were focused onevaluation of reef site, systemic study of the function and structure of the oil platforms,analysis of the scheme regarding platform demolition and artificial reef construction, thechange of flow field and sediment scouring around the reef, and fish attracting effects of thereef. The main conclusions obtained in this research were shown as follows:(1) The local fishery resources need maintenance and recovery, and the terrainconditions, geologic conditions, water quality, water flow velocity, water depth and theecological fishery conditions of Chengdao offshore oilfield meet the requirements forartificial reef construction. The waters south of the trestle of Chengdao CB6A platform canbe used as artificial reef construction area.(2) By taking the steel structure of the decommissioning oil platform as the main frame,allocating artificial reef monomers in the center of and around the platform steel structurerationally, as well as hanging plastic floating bodies on the underwater steel structure, theartificial reef construction project can be done.(3) In the longitudinal direction, flow field effect of reefs occurs mainly in the rangefrom2a/3to20a/3of the reef, very little at20a/3. Mainly lateral influence area is-4a/3to4a/3. Upwelling forms in front of the reef, and the flow velocity at the two flanks of the reefaccelerate with increasing inflow velocity, but its increasing extent gradually reduces. Theregion and height of wake region behind reefs increase with the faster inflow velocity, wake flow velocity will increase correspondingly. Compared to reefs without cover, the flow fieldsof reefs with cover change more serious, and their wake regions are much bigger.(4) With the same flow velocity, the scouring extent around the reef with cover is moreserious than that without cover. The concentration of suspended matter around the reefgradually increases with the increasing of the flow velocity. For both kinds of reefs, theReynolds number generally increases with increasing flow velocity, while the resistancecoefficient decreases with increasing flow velocity. In the case of the same flow velocity andattacking angle, the resistance coefficient of reef with cove is bigger than that without cover,and for one reef with the same velocity, the resistance coefficient of attacking0°is biggerthan attacking45°.(5) The fish gathering effects of the artificial reef monomers are much better than thereis no reef existence, with the biggest difference on fish gathering rate being29%. For thereef with the same shape, the fish gathering effect of the reef with holes is better than thatwith frames. For the reefs with different shapes, the fish gathering effect of the cube reef isbetter than that the triangular pyramid reef.(6)15months after the completion of reef cluster construction, its height is almost thesame as that of13months before, and there is no apparent collapse, indicating that it hasgood stability. Compared with the control area, the biomass of phytoplankton around the reefarea has increased, and that of zooplankton as well as benthos has decreased. This is possiblybecause the latter two are consumed by fish. In the reef area, the stock density of fisheryresources is higher by a multiple of1.6than that in the control area. |
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