High Resolution Sequence Stratigrapgy And Sand Body Quantitative Research Of Putaohua Oil Layers Of Songfangtun Area In The North Of Songliao Basin

The quantitative study of sequence stratigraphy and distribution of sandbody has been done on Putaohua reservoir in Songfangtun area, using the data of core, laboratory analysis, well logging and seismic, realized by computer, under the direction of high resolution sequence stratigraphy theory and reservoir quantitative description theory. After comparing the advantages and disadvantages among different methods of stratigraphic classification and correlation, the method available to the study area is found on the base of the former researches by others. And then the high resolution sequence stratigraphic classification and correlation of bone sections is started, which are interregional and cross the densest well network, and the knowledge of the characteristics of strata and the general deposition of Putaohua reservoir in Songfangtun area applies strong bases for this work.The plan for stratigraphic classification, which is suitable for the study area, has been established, after summing up the former achievements by others about the classification of Cretaceous in Songliao basin. On this base, the high resolution formation skeleton of Putaohua reservoir in Songfangtun area is built up, dependent on the stratigraphic classification of several north-south and east-west bone sectons through the whole area. moreover, the relationship between Putaohua reservoir in Songfangtun area and the one of placanticline in Daqing oilfield has been founded through the classification and correlation of bone sections in both areas.The target stratum of the study area are equivalent to PI1～PI3 of Putaohua reservoir of placanticline, and it can be divided into one symmetric long-basal level-hemicycle, two medium-basal level-cycles, and twelve short-basal level-cycles. And four potential stratigraphic models are discussed separately, and then the stratigraphic model is found that the strata were onlap zone by zone with the source. Through the detailed study, it is concluded that the horizones in the north were thick, while the ones in the south were thin, and that the strata of the lower three short-basal level-cycles p1900, p1800 and p1700 ordinally became thinner, and ultimately died out southtowards.This paper does genetic anatomy to single sandbody in the densest well network beside the formation skeleton, and analyses the microfacies. It confirms that it was fluvial dominated shallow delta, and then generalized its characteristics. The main microfacies are distributary channel, intrachannel sand and intrachannel mud microfacies in delta plain subfacies; and underwater distributary channel, underwater intrachannel sand and underwater intrachannel mud microfacies in inner front subfacies; and relic underwater distributary channel, sand sheet and distal bar microfacies in outer front subfacies; and prodelta mud microfacies, and so on. The vertical evolution suggested the control of basal-level to microfacies: the basal-level descent in the early stage of Putaohua Formation, and sediments migrated towards lake, and formed a shallowing-upward sequence that it was prodelta, outer front, inner front and delta plain ordinally from bottom to top; while in the late period, the basal-level ascent, and sediments migrated towards land, which formed a deeping-upward sequence that it was delta plain, inner front and outer front ordinally from bottom to top.Lastly, this paper studies the distribution of sandbody quantitatively. Firstly, it defines the objects, such as the sandbody of distributary channel, abandoned channel, intrachannel, underwater distributary channel, underwater intrachannel, relic underwater distributary channel, sand sheet, and the inner, middle and outer of distal bar. Secondly, it gets the index for quantitative study, and selects ten parameters such as average value, standard difference, bias angle, peakedness of sandbody thickness, width, width to-thickness ratio, length, length to-thickness ratio, channel offset amplitude angleα, and channel offset amplitude normal angleβ, and so on. Different index has different characteristics and they can reflect the individual sedimentary characteristics and the distribution of sandbody of different type.