| Under the guide of sedimentology and high-resolution sequence stratigraphy, this paper determines features of sedimentary dynamics in each secondary base-level cycle and divides III Oil Formation of He-3Member in Jinglou Oilfield into one rising semi-cycle, one descending semi-cycle and13short-term cycles by using core information, drilling data, logging data and core analysis data. It establishes the high-resolution sequence framework of III Oil Formation in He-3Member and summarizes the technical method of high resolution sequence stratigraphic correlation for the fan delta.With several provenance analysis methods, the paper determines that the sediment of III Oil Formation in He-3Member is not only affected by the near-source Changqiao fan delta in the southeast, but also by the far-source Gucheng delta front in the northeast, known as a secondary provenance. The paper establishes the high-resolution sequence framework, studies microfacies in short-term cycles and analyzes their features of the vertical evolution and plane distribution under the control of two provenances.The study shows that Ⅲ Oil Formation in He-3Member is mainly near-source fan delta environment and develops delta-front facies as well as pro-fan delta facies. The sand bodies mainly are underwater distributary channel sand and thin layers of river-controlled sand that developed along provenances. The sedimentary period of SSC2short-term base-level cycle is the maximum water receding period. During the developing period of each cycle, the provenances are all from southeast. However, the material supply and sedimentary characteristics are different and there is an explicit difference in sandstone distribution laws in each cycle. Within distribution ranges, sand bodies in each cycle have a continuous distribution and mainly are developed in SSC6-SSC3and SSC11-SSC8, featured with continuous distribution and thick layers alternate with thin ones. Overall, the high thickness values are sheet-like distribution in the south, evolving into strip-like distribution in the north. The extending direction is mainly southeast-northwest. In SSC2, distribution ranges of sand body in the south are relatively small while those in the center are not developed, and those in the north are thick due to the influnce of northeastern and northern provenances. Sand bodies in other cycles are mainly developed in the south and center while few are in the north.Through single-well microfacies analysis and partition for cored wells, the paper determines that sub phases in the study area mainly are fan delta front and pro-fan delta, further subdivided into central sand body of main channel in underwater distributary channel, sand body along the river side in underwater distributary channel, underwater overbank sand body, debouch bar, front sheet sand, gravity flow, shunt between the bay and front fan delta mud, totally8microfacies types. It establishes typical logging phase modes and depicts microfacies distribution laws in plane.Based on reservoir charateristics, the paper establishes identification standards of shale, physical properties and calcium intercalation, describes intercalation distribution laws in plane and vertical section in detail and explicitly points out their roles in controlling steam flooding for heavy oil. Most intercalations between cycles are stable except for unstable ones between SSC4and SSC3, SSC5and SSC4, SSC9and SSC8. Interlayers developed within cycles are complicated. By utilizing thickness, interlayer numbers, distribution frequency and the distribution density to characterize them, it shows that overall, most interlayers within cycles are distributed unstably in plane and hard to laterally correlate and trace. The interwell communication is in poor condition.Combing with the production performance and utilizing the study result of reservoir sedimentary microfacies as well as reservoir physical property distribution laws, the paper evaluates the development effect of the study area and identifies the development degree within the oil-bearing area in each cycle. It summarizes the following points. In the south and center of study area closed to southeastern provenance, thickness variation ranges between the central sand body in underwater distributary channel and sand body along the river side or underwater underwater overbank sand body are riched in remaining oil. According to the combination of intercalation distribution features and the production in III Oil Formation of He-3Member, areas near intercalations are also abundant in remaining oil for potential trapping after the steam flooding for heavy oil reserviors. At the same time, cycle combination mining can be taken into consideration in well blocks that are developed with stable intercalations. |
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