The Description Of Chang4+5Reservoir, Yanchang Formation In DT40071Well District Of Luopangyuan Area

According to a lot of drilling, logging, samples analysis and oil test data, the stratigraphicdivision and correlation, structure, distribution of sedimentary microfacies and sandbodies,characteristics of reservoir petrophysics and oilness of the Chang4+5reservoir, YangchangFormation, Upper Triassic Series in DT40071well district, Pangluoyuan area, Dingbian oilfieldhave been thoroughly analized, the enrichment rules of oil and gas has been discussed, using thetheories and research methods of sedimentology, reservoir geology, petroleum geology, logginggeology. On the basis of recongnition of oil and gas enrichment rules, the favorable areas havebeen predicted and the petroleum geological reserves have been calculated. The main results ofthis paper are follows:(1) Based on regional mark layers and sedimentary cycles, the Chang4+5oil-bearingformation can be divided into2subgroups, i.e. Chang4+51and Chang4+52. The structures of thetwo subgroups are all monocline tilting to the west with some small nose-shaped uplift localitily.The structures present feature of inheritance.(2) The Chang4+5oil-bearing formation in the study area is a set of delta deposition whichwas developed by rirer flowing into lake. Delta front subfacies was mainly developed within thework area. The microfacies of subaqueous distributary channel, sub aqueous natural levee, subaqueous distributary bay and mouth bar can be identified from the Chang4+5formation.Vertically, the scale of the delta deposition presented the tendency of decrease from Chang4+52.to Chang4+51.(3) The lithotype of the Chang4+5reservoir in the study area are mainly lithic arkose andarkose. The physical properties of the reservoir are poorer which belongs to low porosity–extralow permeability reservoir. The reservoir space is mainly dissolution secondary pores.(4) According to lots of oil test and production test data, qualitative and quantitativeexplaination results of oil layer and aqueous laye, the lower limit criterion to distinguish oil layerand oil-water layer has obtained, that is: the lithology is fine sandstone, the oil-bearingoccurrence is oil stains, Φ≥7.5%, Δt≥217μs/m, Rt≥10.m, So≥57.0％for oil layer, So≥38.0％ for oil-water layer.(5) The Chang4+5reservoir in study area belongs to lithologic reservoir. The distribution ofoil and gas is controlled mainly by sedimentary microfacies. The subaqueous distributarychannel sandbody is the main site of petroleum distribution.(6) On the basis of the distribution of sedimentary microfacies and sandbody and consultingthe reservoir thickness, petrophysical properity, the lower limit value of oil saturation and oil testdata, the favorable areas of the Chang4+5reservoir have been predicted. The predicted acreageof Chang4+52is8.408km2with geologic reserve360.00×104t (422.04×104m3). Thepredicted acreage of Chang4+51is5.054km2with geologic reserve68.91×104t (80.79×104m3)..