Sequence Stratigraphy And Sedimentary Microfacies Of The Upper Third Member Of The Shahejie Formation In The Xiliu 10 Fault Block

Xiliu 10 Fault Block is located in the north of Xiliu Structure in Lixian Slope Zone, and upper submember of the Third Member of the Shahejie Formation is the main oil-bearing series in the area. In view of the problems existing in the oilfield development and the current situation of insufficient accuracy existing in stratigraphic division and sedimentary facies research, the thesis utilized well logging data, mud logging data and core data to study on the high-resolution sequence stratigraphy and sedimentary microfacies characteristics of the target stratum in the study area, with the guidance of the theory of high-resolution sequence stratigraphy, logging geology and sedimentology. The study had a very positive impact on the improvement of the research precision of the area and the sustainable development of the oilfield.After the comprehensive study on the type, property, scales and distribution of different levels base-level cyclic sequence surface of the target stratum of study area, the sequence boundaries which can be divided into three levels (III, IV, V), or two categories and five small classes, were identified to determine the dividing scheme of high-resolution sequence stratigraphy, with well logging data, core data, mud logging data, seismic data and regional geological data. The upper submember of the Third Member of the Shahejie Formation was divided into a long-term base level cycle (LSC1), three medium-term base level cycles (MSC1?MSC3) and six short-term base level cycles (SSC1?SSC6). On this basis, through the sequence stratigraphic division and closure contrast, the high resolution sequence stratigraphic framework was established, and the development characteristics of the strata and sand body in the sequence stratigraphic framework were analyzed in detail as well.Braided river delta plain and front subfacies were mainly considered to be the main development type in the study area, by the research of petrology and grain size distribution characteristics, sedimentary structures and logging-sedimentary facies marks of the upper submember of the Third Member of the Shahejie Formation. The braided river delta plain mainly included distributary channel sand deposits, overbank deposits and abandoned channel deposits. The delta front subfacies could be subdivided into four types of microfacies which are underwater distributary channel, interdistributary bay, sheet sand and debouch bar. Moreover, the sheet sand and debouch bar were only scattered. Based on the above work, according to the analysis results of single well facies and well-tie sections facies, the sand body thickness contour map, ratio of the sand and formation contour map and plane figure of sedimentary microfacies were drawn, and the location of the shoreline and distribution of sedimentary facies was clear in each of the short-term base level cycles.The sedimentary facies model and depositional evolution of the target stratum in this area were summarized. On the whole, it was considered as a set of shallow water braided river delta plain and front subfacies deposits formed in the basin return period while the sheet sand and debouch bar were not easy to be preserved because of the strong progressive erosion. In the SSC1?SSC2 period, the main development of the area was the braided river delta front subfacies. The delta continued to the southeast to receive sediments, and the distribution area of delta plain and delta front were roughly equal during the period of SSC3?SSC4, which was the most development period of the sand body. Since the SSC5 period, because the climate begun to become dry and the water continued to be shallower, the lake gradually withdrew from the work area. The region mainly developed delta plain subfacies, but the overbank deposit was the most important sedimentary microfacies type in the period.