Reservoir Characteristics Of Huoshiling-Yingcheng Formation In Dehui Fault Depression,Songliao Basin

The Dehui fault depression is located in the southeastern Fault Subsidence Zone of Songliao Basin,which is NNE trending and has a fault depression area of about 4053 km~2.The fault depression period consists mainly of the Lower Cretaceous Huoshiling Formation,Shahezi Formation and Yingcheng Formation.The stratigraphic-structural framework of the study area was established by interpreting the seismic data in the area.The results show that Dehui fault depression is an asymmetrical double-fault structure controlled by several NNE-trending basin-controlling faults,which constitutes a two-concave and one-convex structural pattern as a whole,i.e.the Eastern Sag belts and Western Sag belts and the Central Uplift.The strata are characterized by NNE-trending zonal distribution with thin middle and thick sides.During the Huoshiling Formation,the deposits were mainly in the south of the fault depression,and the strata were thin in the north and thick in the south.The sediments in the northern part of the fault depression were relatively developed,and the sediments migrated to the north in Shahezi period.The southern part of the fault zone in the Yingcheng period was a bulge area,and the most of the sedimentary area migrated to the north,and the sedimentary thickness was increased.Combining core,well logging,seismic and single well facies analysis,thin section identification and grain size analysis,etc.Four main facies types have been identified in the stratigraphic units of Huoshiling Formation,Shahezi Formation and Yingcheng Formation in the study area,including lacustrine facies,fan delta facies,sublacustrine fan facies and volcanic facies.9 sedimentary subfacies and 17 sedimentary microfacies have been further divided.During the Huoshiling Formation,the fault depression formed a semi-deep lake-fan delta-lake bottom fan-volcanic facies formation system with western,northwest and southeast as the main source supply areas.Duiring Shahezi Formation sedimentation's period,the fault depression constitutes a semi-deep lake-fan delta-lake bottom fan construction system with the southwestern,southeastern and western regions as the main source supply areas.And the Yingcheng Formation developed in the north and northwest,where the southeast is the main source supply area of the shallow lake-fan delta and near-shore-subaqueous fan-volcanic rock construction system.According to the thin slice identification,scanning electron microscopy and sample test analysis,the Degang fault depression and the Yingcheng Formation clastic rocks are mainly composed of lithic sandstone,lithic feldspar sandstone and feldspar lithic sandstone.The rock dominated by medium-grain and unequal-grain structures,and the structure maturity is low.The reservoir rocks are mainly subjected to mechanical compaction,cementation,metasomatism and dissolution,mainly in the A-phase of the diagenetic rock(buried depth 1000~2400m),followed by the B-phase of the diagenetic rock and above(buried depth>2400m).According to the analysis of core physical property test:in the clastic reservoirs of Dehui fault depression,the Huoshiling Formation is mainly of ultra-low porosity and ultra-low permeability,and the pore structure is mainly of type IIIA.The Shahezi Formation is mainly of ultra-low porosity and ultra-low permeability,and the pore structure is mainly of type IIIA and IIIB.The Yingcheng Formation is mainly of low-to ultra-low porosity and ultra-low permeability,and the pore structure is mainly of type IIB and IIIA.In the volcanic clastic reservoir,the porosity of the Fushiling Formation is mainly II~III,and the permeability is mainly V.In the volcanic lava reservoir,the porosity of the Fushiling Formation is mainly II~III,and the porosity of the Yingcheng Formation is mainly V,and the permeability of both is mainly V.Core data,regression analysis and data superposition are used to predict the distribution characteristics of porosity and permeability in each group of fault depression.It is found that the relatively high quality reservoirs of Huoshiling Formation and Yingcheng Formation in Dehui Fault Depression are mainly distributed in the Eastern and Western Sag belts on both sides of the Central Uplift of the fault depression.Lithofacies types and diagenesis have obvious control on reservoir physical properties.Among them,the front subfacies of fan delta has the best physical properties,while the middle subfacies of sublacustrine fan takes second place,and the shore-shallow lake subfacies is worse.Two secondary corrosion pore zones formed by dissolution in 1900m~2400m and2750m~3000m.Based on the above analysis of reservoir characteristics and seismic interpretation,it is shown that there are three favorable reservoir zones in Dehui fault depression.They are the favorable reservoir zone of the central volcanic volcanic sag,the favorable reservoir zone of the east-western sag of the central sag,and the favorable reservoir zone of the updip tipping-out type of the Buhai sag.On this basis,9 favorable target areas are preferred.Among them,the volcanic area of the northwest of Lanjia and the volcanic area of the eastern part of Longwang are Class I favorable target areas.The eastern volcanic area of Huajia,the Lanjiaxi volcanic area,the Huajia uplift tipping area,the Guojia uplift tipping area,and the Helong updip tipping area are Class II favorable target areas.The Dragon King's upturned tip-out area and the Buhai sag-dumping tip-out zone are Class III favorable target areas.