Design And Demonstration Of A Technical System For Rigs-to-Reefs Project

According to the stipulations of relevant laws and regulations, offshore oil and gasfacilities in stop production, if for no other purpose or reason, must be disposed of.Offshore oil and gas facilities disposal is a complex system engineering, which shouldtake many factors into account such as the cost, safety and environmental risk factors.As one of the main disposal scheme of decommissioning offshore oil productionfacilities, Rigs-to-Reefs project transforms the decommissioning platform as artificialfish reef by retaining the offshore platform structure retired in whole or in part andlaying the artificial reef in the surrounding area. This project can not only save thedemolition costs, reduce the risk on operation and the effect on marine ecologicalenvironment, but also can make the ecological function of decommissioning platformbe fully utilized. The retained structures and the artificial reefs can play positive rolesin fishery resources multiplication and ecological environment improvement.Since the USA Minerals Management Service first proposed in1983"Rigs-to-Reefs" project, The researchers from European and America have maderesearch on the Rigs-to-Reefs project from different angle such as the environmental,economic, legal and dismantling technology and so on. But these studies are notinvolved the key techniques in each stage of Rigs-to-Reefs project as a whole from thepoint of systematic induction and generalization, and have not formed a completetechnical system. In China, the Rigs-to-Reefs f project has not been popularized.There are only a few researchers who gave a brief introduction to the Rigs-to-Reefs.The study on the technical system is blank.In2010, China Petrochemical Shengli Oilfield Branch Company carried out the"Rigs-to-Reefs" demonstration project in Chengdao Oilfield for the first time in China.Based on the actual research on demonstration project, this paper takes the entireoperation process of Rigs-to-Reefs project as the research object, and building a framework of Rigs-to-Reefs project technical system as the research purpose. On thebasis of system engineering analysis method, Work Breakdown Structure （WBS）principle and reference related research literature and other relevant laws andregulations framework provisions, this thesis proposes the research mentality and thetechnical route of Rigs-to-Reefs project, and systematically analyzed the technicallinks included in the Rigs-to-Reefs project such as data collection, environment andfacilities investigation, engineering feasibility, platform demolition, the reef designand layout, reef processing and delivery, project approval and follow-up survey andevaluation, etc. The mainly studies and results achieved are following:（1） The foundation, principle and key links for feasibility demonstration ofRigs-to-Reefs project are proposed in this paper. Through analyzing the applicableconditions of Rigs-to-Reefs project, the general principles are discussed, based onwhich the demonstration process is standardized. In order to demonstrate thefeasibility of the Rigs-to-Reefs project, the environmental information of theplatform’s sea area should be fully collected, sorted, and analysed at first, and then thesuitability of the Rigs-to-Reefs project should be evaluated according to somestandards and methods.（2） This paper constructs the technical framework and technical system ofRigs-to-Reefs Project. The whole process including the disposal of decommissioningoffshore oil platform and the utilize the abandoned platform structures for artificialreefs is straightened out, and then every key technology link was analyzed andillustrated.（3） The contents and steps of the tracking survey evaluation after the Rigs-to-Reefsproject are determined. When the Rigs-to-Reefs project ends, the acceptance of workis needed, and the ecological environment effect of the project should be investigatedand evaluated. For those which do not reach the original expectation, it should beadjusted in a timely manner after seeking the reason from marine environment, overalldesign, design of reefs, and other aspects.（4） Through the study of marine water environment and ecological system, the reef address is determined and the reef site suitability evaluation is evaluated. The resultsshows that the terrain, geological conditions, water quality conditions, the water flowvelocity, water depth and the ecological fishery conditions of the sea area whichChengdao Oilfield locates all meet the site selection requirements. Therefore, wechoose the north sea area of CB6A platform in Chengdao Oilfield as the location ofRigs-to-Reefs project.（5） This paper analyses the environmental effect of the Rigs-to-Reefs project on thesea water and sediment in the area. Compared with the control area, the suspendedsolids concentration of fish reef zones increase significantly which maybe owing tothe upwelling caused by fish reef construction. The upwelling brings the nutrientexchange between the underlying and the surface water, increasing the nutrientcontents(NH₄⁺-N, NO₃--N, COD, PO₄³⁺, TP, etc.) of the sea water and improving themarine primary productivity.（6） The effect of the Rigs-to-Reefs project on the ecosystems and fisheriesresources of this sea area is studied. The results shows that the reef group height ofwhich it is constructed after15months is similar with that after2months. The reefgroup do not collapse, showing a good stability. Compared with the control area, thephytoplankton quantity increases after the reefs were placed, while the quantity ofplanktonic and benthic animals decrease. This may be related to the fish ingestion ofPlanktonic and benthic animals. The density of fishery resources in reef area is higherthan the control area, and the former is about1.6times of the latter.