Evolution Process and Historical Reconstruction of Meandering River:An example from Fuyu oil reservoir of Yangdachengzi Oil Production Plant in Jilin Oilfield

Key words: 
• meandering river /
• riverway evolution /
• lateral accretion bodies /
• deposition process /
• architectural structures of sandbodies

Abstract: Fluvial-delta reservoir architecture has been another geological hotspot over the past 20 years, and many scholars constructed geological models based on different perspectives and different research methods. However, the underground reservoirs are extremely complex which are composite sandbodies and reformed frequently, not single cause, such as there is erosion, cut and discarded phenomena etc. when channels swing and migrate, which make the sandbodies complicated in a certain extent. The wrong conclusions and understandings are drawn easily and make the complex reservoirs originally crude and simplistic if can not start from the causes of evolution, but describe results of the deposition directly. All of these will be not conducive to adjust for the late oilfield.
The natural flow barrier from point-sandbar deposit of meandering river is a main controlling factors for residual oil, and its scale is small, difficult to identify, research difficulty and more need of information and other restrictions, which restricted the fine dissection of the point bar. Authors will rebuild the historical evolution of meandering rivers by reconstructing process of channels deposition process from semi-qualitative and semi-quantitative point of view in order to make the reconstruction and result more reasonable.
The Yangdachengzi oil-bearing formation in Fuyu Oil Production Plant of Jilin Oilfield is main object of this study. Fuyu oilfield locates in No.3 Fuxin uplift structural belt in the eastern edge of the southern Songliao Basin, and the dome anticline is complicated by faults. The reservoir mainly is controlled by structure belonging to crack, low permeability lithologic reservoirs in which distribution are relatively stable, and the lithology are mainly siltstone and fine sandstone. The previous research results show that the meandering river deposition was most developmental facies type in Yangdachengzi oil-bearing formation in Fuyu field under fluvial-delta deposition background.
The lateral accretion body size, orientation and inclination were identified by making full use of the core, logging, oil and other dense well net, point bar sand body identification, restoration, river fitting parameters and estimation methods based on previous sedimentary facies research, and then the course of sedimentary evolution was reconstructed according to the rule of meandering river development after the contemporaneous lateral accretion bodies were linked and built up from single stage fluvial sand bodies combined with geological conceptual model. This method could explain the problem of overlapping regular pattern and architectural structures of sandbodies from the angle of cause and process quite well, so, the explanation will be more reasonable and credible to predict the potential of residual oil based on architectural structures of sandbodies from the angle of deposition process and deposition result. By using the above methods, the reconstruction of meandering river sedimentary evolution history was completed in the thin layer small-scale. Practical results show that the evolution of the meandering point bar historical reconstruction provided the solid foundation for the fine anatomy of meandering channel sandbodies, and effectively guide the remaining oil forecast and tapping potential in advanced stage.