The Corrib GasFieldi nt he SlyneB asinl iesabout 70 kmw est ofC o. Mayo,offshoreI reland.The basinisanarrow Triassic/Jurassic half-grabenandisoneofaseriesofstructurallylinked basins thatarepresent alongthe west coast ofI relanda ndthe BritishI sles. The fieldwasdiscovered in1 996 byw ell 18/20-1, encounteringa61 mgascolumn inlow-porosity Triassic fluvialsandstonesatasubsea depthof3539.6 m. Using extremely poor 2Dseismic data, itw aso riginally mapped asatilted fault block, witha nassociated rollover structureto the east. The dataquality wasp articularly poor dueto the near-surface Palaeogenevolcanicst hat contributeto energydispersion andextrememultiplegeneration.A3Dseismic surveywasacquired in1997 and resulted inamajor improvement indataquality,a llowingi mproved structuralinterpretation thats howed the Corrib Fieldto be afaulted anticline.The subsequent appraisalwell,18/20-2z,drilled approximately 1kmfrom the subsurface location of18/20-1,penetrated a185 mgascolumn infairtogoodquality sandstone.Ittested dry gasatastabilized rateof62.87 £ 10 6 SCF/don a2 00 choke.Reprocessingofthe seismic data, alongwiththe successful drillingofthe followingwell 18/25-1,confirmed the fieldto be arelatively simpleanticlinaltrap,with acomplexfaulted overburdenthatisstructurally detached from the reservoirbythe Mercia Halite.The source rock isassumed to be the WestphalianCoalMeasures,similartothatencountered bywell 27/5-1. The dry gasis consistent withaType-III humic source rock.The reservoirisbiostratigraphically barren,consistingoffluvialred bed sandstone, andi sassumed to be ofT riassic SherwoodS andstoneG roup equivalent age.The unitis approximately 400 mt hick, consistingofahigh net-to-gross sequence oflow-sinuosity braided fluvialchannel sandstoneswithsubordinatesand-flatandplayamudstonedeposits. Onamacro scale, itisaremarkably uniform sandstonewithonly subtlefaciesvariations,but on amicro scalethereisasignificant variation ingrainsizeand cementation,which affects reservoirp roductivity. Mineralogically,therea red istinctdifferencesfrom the SherwoodS andstoneG roup ofthe East IrishS ea, indicatingthatt he SlyneE arly Triassic systemw as depositionallysimilarto,but distinctandseparatefrom,thattothe east ofIreland.Dipmeterdataindicated that the rivers ystemflowed from the SW to NE, essentiallyalongthe direction ofthe present-daySlyneB asin, suggestingthatitwaslargely sourced from the southinthe Variscanhinterland, but withevidence ofsediment input from localhighssuch asthe ConnemaraMassif.