| Shengli oilfield in Chengdao Seas was the first offshore oil field in our country.There were more than one hundred subsea pipelines and water pipelines from1993when the first oilfield were product. The subsea pipelines were the main ways oftransportation for the oil and gas, so it played an increasingly important roles on thesecurity and efficient production. In recently years, the survey data showed that therewere many problems needing reasonable and effective governance, such as theerosion severely around the oil platform, bareness of the pipes and free spanning.There were many reasons for the bareness of the pipelines and the free spanning,where there were two mainly aspects. Firstly, because of the scouring and erosions bythe wave, tidal and other water-power on the seabed, the buried subsea pipelines werebared and free spanned. The existence of oil platforms, pipelines and other artificialmarine structures caused differences of erosion, where exacerbated the scouringbetween the subsea pipeline and the surrounding seabed, making it more prone to bareand free span. Secondly, unstable geological factors, such as submarine landslides,collapse pits, erosion relicts, underwater slopes and so on, caused changes of theseabed topography probably, resulting the bareness and the free spanning of thesubmarine pipelines. The majority of the pipelines with bareness and free spanningwhich caused by erosion differently were around the oil platforms piles.Traditional treated methods were mainly supporting by piles, filling withsandbags and gravels, trenching and burying, and so on. Those methods might play aprotective role in the temporary, but would cause secondary scour from the seabed.Implement one way singly on deal with the free spanning of the submarine pipelineswas not appropriate in Chengdao seas. We had achieved good results that the introductions of bionic grass processing methods for the free spanning and barenesssubmarine pipelines in Shengli Oilfield from2006.Bionic grass processing technology was a new type of anti-erosion techniques onthe seabed which developed basing on marine grass bionics. Bionic grass wasprocessed by a new types of polymer materials which could resistant the immersionand the long-term erosions of the sea water. It could lay on the seabed by the installedbases and the anchoring devices designed specially. When the water flowedthrough the bionic grass, the wave could be absorbed and weakened, begetting thevelocity of the flow decreases and the ability of scouring mitigation to the seabed.Since the lower velocity of the water and hinder of the bionic grass, the sedimentscarried by the water would deposited onto the bionic grass installed base padcontinuously under its own gravity, so it could play the role of sand fixation andsiltation. After laying bionic grass, the most obvious effects achieved were to reducewater flow velocity and promote settling of suspended sediment. It found that thebionic grass could reduce the flow velocity at least15%-20%by actual measurementand calculation. It could precipitation more than160kilograms of the sediments a dayin the10meters multiply by30meters of the bionic grass.Seabed topography and the treatment effect of the bionic grass were explored inChengdao seas from2008to2013in Shengli Oil field. In this paper, we had studiedthe effects and the suitability of the submarine pipelines with free spanning whichgoverned by the bionic grass technologies,based on the collection, collation andanalysis of the data. We had achieved good overall results after implementing thetechnical of the bionic grass by a large number of survey data, firstly. Because of alarge number of sediment concentration which were mainly composed of coarse siltand clayey silt composition, high concentration of suspended sediment in YellowRiver, bionic grass technology could play an important role in promoting the silting ofthe sediments. There were many scouring pits around the end of the group platform ofoil wells in Chengdao seas, and the problems of the bareness and free spanning werevery serious by the monitoring data of the bionic grass in recent years. The effectswere not very satisfied that the combination treatment between filling with sandbags or gravel and bionic grass. Constrained by strong scour around the piles near the oilplatforms, bionic grass technology for effects of the platform near the pile were notappropriate for the bareness and free spanning submarine pipeline, so this issueremained to be studied and improved in the future. |
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