The Condition Of Petroleum Reservoirs Formation And The Prediction Of Favorable Regions In The The Northern Part Of Qaidam Basin

Based on previous research results,this paper focused on the genetic types of natural gas,hydrocarbon source rock distribution,the favorable reservoir facies belt,high quality guidance system,source reservoir allocation relation and reservoir comprehensive analysis research for the exploration field of coal type gas in the area of the northern margin in the Qaidam Basin.Therefore,it cleared the oil and gas distribution and controlling factors of hydrocarbon accumulation of the northern margin in the Qiadam Basin to point out the favorable exploration direction of coal type gas.According to the carbon isotope data,natural gas of the northern margin in the Qaidam basin is mostly typical coal type gas.The mixed alkanes of different sags from the same resource and different resource results in the isotope to be“upside down”phenomenon in some area.So the natural gas distribution shows zonation in plain.lenghu3 is dominated by oil but in Dongping,Eboliang and lenghu7 is mainly gas.Both of oil and gas are distributed in the area of Niudong,Maxian and Saishenteng.The distribution of oil and gas is controlled by the maturity of source rock.The establishment of fault-depression transformation mode of Jurassic strata and the stratigraphic distribution of faulted period and depression period.They have obvious inheritance in deposition.It is pointed out that their existence of Jurassic sag in Hongsanhan and Jianbei area.The residual of high quality Jurassic source rock mainly developed in the depression period and the hydrocarbon generation center located in Yibei and Lenghu area.Three inherited source system of tertiary developed in the north margin of Qaidam Basin.The sedimentary system is mainly the alluvial fan,braided river to?fan?braided river delta to lake facies.The physical property of clastic reservoir is controlled by sedimentary facies belt,diagenesis,cementation,dissolution and stress.The space of tertiary sandbodies is mainly primary pore and the high quality reservoir mainly developed in basin margin of ancient uplift.The reservoir space of Jurassic sandbodies is dominated by secondary pore and there have better reservoir physical prope in Niudong area.The bedrock reservoir has become one of the important fields for oil and gas exploration.The lithology of bedrock reservoir is mainly granite,metamorphic rock and basic rock.The weathering crust in the longitudinal direction can be divided into three layer and the pore types include the pores,cracks,dissolved pores and dissolved fractures.Therefore the lithology,stress and rock weathering is the master control factor of reservoir and the nearby places of the deep fault in the edge of the basin are the favorable bedrock reservoir development zone.Three inherited palaeohighs of the eastern part of Altun Mountains,the frontland of Seshentengshan and Mahai to Nanbaxian are the long-term pointing area of oil and gas migration.The four counseling models of fault-unconformity,fault-transport layer,fault-fault and fault composite guidance develops and the accumulation from outside of source,the accumulation from the above of source and the accumulation from the inside of source exits.The ancient uplift and slope of basin margin is dominated by the accumulation from outside and inside of source and the late tectonic belt is the accumulation from the above of source.Reservoir physical simulation experiments confirmed that the thin-bad sandstone also have better gas-bearing properties near the shallow fault in the late tectonic zone.Exploration potential is high in the deep complete trap.Planar distribution of gas in the basin is controlled by the maturity of effective source rocks and the strength of hydrocarbon.The major accumulation model is proximal plays and beneath-source plays which is determined by the relationship of source and reservoir The key factor of hydrocarbon accumulation is whether there is the fault could communicate with the source and pathway system the basin thrust fault zone,palaeohighs and the late interior basin compressional tectonic belt which is near to the hydrocarbon center is the gas-rich region.The N₁-N₂¹ in the basin is the main exploration target.The E,J and bedrock weathering crust is the main exploration target of the basin margin.The three palaeohighs and the complete trap of Eboliang-Lenghu tectonic belt is the favorable exploration direction of coal type gas.