The Analysis Of Deep Water Turbidite Reservoir Architecture And Remaining Oil Distribution

Wen-95block in Zhongyuan Wennan Oil Field is located in the south of Wennan Structure of Dongpu Depression, and it’s a horst block between Wenxi III Fault in the west and Wendong Fault in the east. Through30-year development, the research area has stepped into the exploiting stage of high water cut/extra-high water cut. The distribution of remaining oil becomes increasingly complex, and a appreciable amount of remaining oil is distributed in long-term water flooding oil deposit in different scales and different forms. In order to enhance the oil recovery efficiency and maintain the continuous high and stable yield of the oil field, it requires careful researches on the distribution and controlling factors of the remaining oil in middle and later periods of water flooding.Based on theories like sedimentary petrology, logging geology, reservoir geology and development geology and guided by deposition law and deposition model of deep-water turbidite, the author of this paper carefully studies the control action mode of the formation and distribution of the remaining oil with regard to the above questions by fully dissecting the reservoir structure.The researcher applies the oil shale marker formation that can be traced and compared within the region and other mudstone auxiliary marker formations to carry out a detailed stratigraphic division and correlation in the whole region. Based on this, the generally developmental monosandbodies in the work area are selected to complete the stratigraphic correlation skeleton profile of the monosandbodies. The profile shows that the overall research area is a NNE-orienting monoclinic structure which is relatively higher in northeast and lower in southwest, and the small fracture inside the fault block is well developed; due to the influence of Wendong Fault, Wenxi III Fault and the internal fracture, lacuna generally exists in the work area; monosandbodies mainly exist in the longitudinal direction, and sand-mudstone appears alternately; in the transverse direction, sand bodies are distributed in sheets, with obvious phase transformation characteristics.Based on the fine isochronal stratigraphic framework, and through the analysis of sedimentary facies symbol like lithology, structure and paleontology, the researcher holds that there are two depositional models developed in the stratum of Wen-95block S3, namely fan delta and deepwater turbidite fan, and the middle fan intrafacies are divided into6microfacies including underwater branch channel tip, underwater levee, lobe between the channels, estuary lobe, sheet sand and mud floor. The flat characteristics of depositional microfacies show that Wen-95block is a multi-provenance deposition, and the origins of deepwater turbidite fan in different times vary very much.3genetic types of fan are developed in the research area:(1) lobe caused by single branch distributary channel which has small-scale water channel inside the fan and is mainly dominated by sheet sand deposition;(2) lobe caused by dendritic branch distributary channel whose sand body inside the fan is mainly dominated by lobe deposition and that inside the water channel is developing in branch shape in the root of the fan;(3) lobe caused by flake channel, whose sand body inside the fan is thick, and the lateral migration phenomenon of underwater distributary channel can be seen.Based on the relevant knowledge of modern outcrop deposition and domestic and overseas experts’ study of various types of subsurface reservoir structure, the researcher holds that the analysis of deepwater turbidite fan reservoir structure can be divided into3stages:first, make sure the single deepwater turbidite fan body; then, mark off several complex water channels (lobe) in the fan; finally, recognize single water channel (lobe) in the complex water channels. The research results show that the monosandbody wall of deepwater turbidite fan in the research area is well developed, the interlayer heterogeneity is strong and the relation of sand body overlapping features various types. There are four types of multi-phase monosandbody overlapping, namely, lateral bifurcation, sandstone and mudstone alternation, lateral pinch-out and false connectivity; there are two types for the same-phase monosandbody, namely, horizontal off and thickness mutation. Among them, the lateral bifurcation in multi-phase monosandbodies is the most common type of structure in the research area, as well as the important geological factor of remaining oil enrichment after the development.On the basis of structure research and dynamic analysis, the remaining oil distribution patterns of complex water channel (lobe thick sand) scale and monosandbody scale are established. On the basis of pattern analysis, the further digging direction of remaining oil is indicated, and surface phase transformation and interlayer interference are believed to exert obvious control effect on the distribution of remaining oil. In addition, part of dry layers own certain movable crude oil reserves, and the output can be improved through acid fracturing.