| Orinoco extra-heavy oil belt is one of those extra-heavy oil belts which have not been exploited on a large scale,and it has an extremely huge development potential.In order to exploit the remaining heavy oil,it is extremely urgent and important to carry out the detailed basic geology research.However,several problems do exist during this research,such as the complexity of the inner reservoir architecture,the incomprehension of the reservoir characteristics and the unclearness of the features of the distribution of sand bodies.Then this paper selected the Oficina formation of the MPE-3 work area which is at the Orinoco extraheavy oil belt as the research object,and we started to research the features of the reservoir architecture on the basis of the sedimentary research.The research analyzed the former stratigraphic classification schemes in detail.On the basis of newly added well data,the paper firstly did the stratigraphic subdivision and correlation work.Then we started detailed research on the reservoir architecture of the braided delta on the basis of exhaustive research on the isochronous stratigraphy framework and the sedimentary model.By observing the lithology,granularity,sedimentary structures and colors of the cores and slices,different types of lithofacies were recognized,and different types of lithofacies associations were identified.Different hierarchical levels of bounding surfaces had been recognized by several methods,which include core identification method,well logging information identification method and seismic data identification method.Connecting the research results of sedimentary facies and the features of different architecture elements,we recognized several types of architecture elements,and we studied the plane distribution and section spread features of the main architectural elements At last,the paper discusses the effects of reservoir architecture on the formation and distribution of remaining heavy oil.According to the research,we had several new findings:(1)The paper summarized a reasonable and complete layer division and contrast scheme,and eleven main stratigraphic profiles had been built.(2)The Oficina formation is a large set of sedimentary strata which developed in the fluvial and delta background.The lower Morichal member belongs to the braided river deposits of the braided delta plain,while the middle and the upper Yabo member and Jobo member belong to the braid-river delta front subfacies.(3)Twelve types of ithofacies were recognized,and eight types of lithofacies associations were identified,and the knowledge base was built.(4)Three kinds of surface-identification methods which help to recognize different hierarchical levels of bounding surfaces had been proposed.And this paper built two different bounding surfaces classification schemes of braided river deposits of the braided delta plain and the braid-river delta front subfacies.(5)We recognized composite diara dam,braided channel,floodplain in the braided river deposits of the braided delta plain(the lower Morichal member).And the other four elements had been recognized in the braid-river delta front subfacies(the upper Yabo and Jobo member),which include the underwater distributary channel,inter-distributary bay deposit,river mouth bar and sheet sand.Then the paper proposed the two different architectural elements classification schemes of braided river deposits of the braided delta plain and the braid-river delta front subfacies.(6)The distribution patterns of the main sand bodies of different layers have been found out,and the development model of the architectural elements in the main target stratum have been summarized.(7)The existence of bounding surfaces and the muddy architectural elements leads to blocking effect,and it has an effect on the formation and distribution of remaining heavy oil. |
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