New understanding of remaining oil distribution in oil reservoirs at extra-high water-cut stage:A case of Upper Ng3 sand group in Zhongyi area,Gudao Oilfield
Extra-high water-cut stage is an important period of continental reservoir development. Study on remaining oil is the basis of enhanced oil recovery in the oil reservoirs at extra-high water-cut stage. Based on data of three sealed coring wells and 17 newly drilled wells at extra-high water-cut stage in Zhongyi area of Gudao Oilfield,the distribution characteristics and enrichment regularities of the remaining oil are analyzed from plane,interlamination and interlayer. The results show that remaining movable oil distributes broadly and enriches locally at extra-high water-cut stage,which is also verified by the dynamic production behaviors of the oilfield. Based on interlayer distribution pattern and rhythm of the reservoir,three local enrichment modes of the remaining oil are established,including whole-barrier type,half-barrier type and rhythm type. The half-barrier type may be further classified into oil well barrier type,water well barrier type and cross-well barrier type. The rhythm type can be further classified into positive rhythm type and uniform type. The new results change the traditional understandings of high dispersion and local enrichment of the remaining oil at extra-high water-cut stage,which has important significance on tapping the potential of remaining oil in fluvial facies of old oilfields.