Hydrocarbons prospectivityud• The East Irish Sea Basin is at a mature exploration phase.ud• The hydrocarbons-prospective sedimentary basins are characterised by sourceudrocks, an abundance of structured regional petroleum reservoir and seal rocks andudby suitable timing of geothermal events for generation and transfer of petroleumudproducts from the source rocks to the reservoir rocks.ud• SEA6 has regionally diverse seabed habitats which vary significantly from area toudarea in currently licensed acreages in the eastern Irish Sea. The variations inudseabed habitats have been systematically related to the sedimentary processesuddriven by quantifiable patterns of mean seabed stress.udSedimentary Processesud• Open shelf seabed sedimentary processes are driven by seabed stress originatingudfrom interaction of the seabed with strong currents generated by tidal streams andudby waves.ud• The scale of the stress imposed on the seabed and the related seabed habitatudvariability varies from regional (between mainlands, varying shelter aroundudheadlands) to macroscopic (around boulders and pebbles).ud• During the fair to moderate weather conditions characteristic of the late spring,udsummer and early autumn seasons, the seabed sediment types on the openudcontinental shelf are dominated by the stress imposed on the seabed by theudstrengths and flow directions of the peak tidal currents. In this setting most of theudregional variations in seabed sediment types are dominated by the effects of theudcoastal configurations on the tidal streams.ud• In areas where the seabed stress from waves is dominant, the seabed sedimentsudcoarsen with exposure to the increasing seabed stress generated when the wavesudinteract with the seabed. Seabed stress from waves is dependent on wave powerudthat varies with weather, wave fetch, seabed slope, wave direction and wateruddepth.ud• There are knowledge gaps on possible regional variations of seabed propertiesudwhen the seabed is stressed during extreme weather events associated with stormudsurge and storm waves.ud• In the most highly stressed seabed environments, exposed bedrock and stronglyudcohesive unsorted gravelly, sandy and muddy sediments are often swept clean ofudunconsolidated muds, sands, granular gravel and pebbles. Parts of the seabed inudthese areas may consist of cobbles and boulders. Environments of least seabed stress are characterised by fine-grained muddy sediments. Mobile sandwaves areudcharacteristic of areas where sediments are being transported along the seabed inudenvironments that are situated between the areas of extremely high seabed stressudand very low seabed stress. The sense of regional seabed sediment transfer is fromudand across areas of high seabed stress to areas of lower seabed stress.udThe observations summarised above indicate that if large-scale disruptions to the naturaludseabed habitat are to be avoided, new development scenarios should avoid barriers thatudcould have a significant effect on the regional patterns of seabed stress.ud• As elsewhere on the UKCS, glacigenic sediments and relict static glacigenicudbedforms have had significant regional and local effects on the patchiness of theuddistribution patterns of seabed sediments and seabed habitats.ud• There is a knowledge gap in the research evidence required to securely link subregionaludincreases in the percentage of biogenic carbonate in the sand fraction ofudthe Irish Sea Mud Belt with increased biological productivity of surface waters,udwith methane expulsion from shallow and seabed sediments or with processes ofudbedload carbonate transport.ud• Investigations of shipwrecks and artificial continuous barriers indicate that theudamount of seabed scour is much larger than the profile of large seabed obstaclesudpresented to near-bed current flow. The observations reveal patterns of scourudasymmetry consistent with model predictions of mean peak tidal current speedsudand the interpretations of the directions of regional sediment transport based onudthe geometries of seabed bedforms. Wreck studies could therefore be used toudcalibrate modelling on the likely long term effects of future seabed developmentudscenarios. Shipwrecks have also contributed to seabed diversity.ud• Active pockmarks, bioherms, banks in less than 20m water depth and someudshipwrecks are already regulated by conservation measures. The followingudgeological features are also worthy of consideration for preservation because theyudare irreplaceable:udStatic bedforms — sarns, pingos, upstanding rock outcrops in mud beltsudMobile bedforms — banner banks, estuary banks and spitsud• A gateway for sand exchange between the open shelf and the eastern Irish Seaudcoast off England appears to be defined by a zone situated between North Walesudand the southern limit of the Eastern Irish Sea Mudbelt. Although the currentudprospects for large oil and gas developments in this area are very small, anyuddevelopments that could the patterns of sand exchange through thisudenvironmentally sensitive area should be avoided.
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