Biyang Depression covers an area of 1000 km

2

.Within it

530 km

2

belongs to its north slope.The 4 oilfields discovered before 1985 are distributed in the south slope and the central deep subsided area.In recent years

5 oilfields have been discovered in the north slope

the prospected and controlled hydrocarbon reserves occupies above 40% ofthe total reserves of the depression

and this percentage may even rise as the explor ationcarrying on.Favourable conditions for hydrocarbon accumulation in the north slope are:1.Thesuccessional sedimentation-structure complex slopes are the target area for hydrocar bonmigration;2.Multiple sandbodies provide good reservoirs;3.A series of nose-structuresare in control of hydrocarbon accumulation;4.Two sets of faults provide the conditionof shelter for hydrocarbon accumulation;5.Cap rocks on regional unconformity makeswell preservation for shallow pools in slope.There are various kinds of oil pools

within which fault-nose

fault-block and uncon formity ones are the main types.