简介：ThickenedheavyoilsinChinaaregeneticallycharacteristicofcontinenta.Astotheirphysico-chemicalproperties,theseoilsareveryhighinviscosityandlowinsulphurandtraceelementcon-tents.Inthegroupconstituents,theconcentrationsofnon-hydrocarbonsandasphalteneareveryhighbutthoseofsaturatedhydrocarbonsandaromaticsareverylow.Thegaschromatogramsofalkanesshowthattheseheavyoilshavehighabundancesofiso-alkanesandcyclichydrocarbons.Inallthesteroidsandterpenoids,bicyclicsesquiterpenoids,tricyclicditerpenoids,re-arrangedsteranesandgammaceranearestronglybildegradation-resistent.Theformationofheavyoilreservoirsiscontrolledmainlybylatebasinascendance,biodegradation,flushingbymeteoricwaterandoxidationintheoil-bearingformations.Ac-cordingtotheirformationmechanisms,heavyoilreservoirscanbeclassifiedasfourcategories:weatheringanddenudation,marginaloxidation,secondarymigrationandthickeningofbottomwater.Spacially,heavythickoilreservoirsaredistributedregularly:theyusuallyshowsomeparageneticrelationshipswithnormaloilreservoirs.Heavyoilreservoirsoftenoccurinstructuralhighsorinoverlyingyoungerstrata.Theirburialdepthisabout200m.Horizontally,mostofthemaredistributedonthemarginsofbasinsordepressions.