Sequence Stratigraphy Characteristics And Controlling Factor Of Beach-bar Sand In The Second Member Of Shahejie Formation Dawangzhuang Oil Field

Beach-bar sand is one of the most important sand-body type of faulted lacustrine basin in Meso-Cenozoic Eastren China. Beach-bar sand is mainly express for small sands thickness and irregular sands distribution, the size and development of sandbody within beach-bar sand is far less than alluvial fan, river, delta, turbidite fan and other kinds of sands. Oil-gas prospector was used to show low attention to beach-bar sand. At the present day, with the highly exploration-development of reservoirs and the demand of backup replacement reserve, beach-bar sand has become one of the most important object of exploration for lithologic reservoirin in recent decade, especially in Shengli Oil Field. Beach-bar sand reservoirs has become important object of backup reserve and replacement reserve in Shengli Oil Field.Nonetheless, in different sub-depression, sedimentary characteristics, combination characteristics and distribution characteristics of beach-bar sand are mostly different.Base on the previous studies of beach-bar reservoir in faulted lacustrine basin and summarized regulation which the structural evolution and development history in different sub-depressions are mostly different; exploring the sedimentary regulation should basing on its own evolution characteristic in separate depressions. then, the development regulation of beach-bar sand could be predict and oil-gas explorationdevelopment could be direct efficientlyAs beach-bar kind reservoirs, beach sand, bar sand, carbonatite beach-bar sand and etc. has been discovered by progressive exploration which have good hydrocarbon shows, multifarious reservoirs and rich sedimentary types in the second member of Shahejie formation, Chezhen depressions. Because of the frequently tectonic movement, complicated structural characteristics of sedimentary basement,highly differences with sedimentary dynamics in faulted lacustrine basin, the causes of beach-bar sand body and the controlling mechanism on sandbody have its own characteristic and development regularity. In this paper, the second member of Shahejie formation in Chezhen depress as study object, based on the study of modern sediment, the theory of sequence stratigraphy and interpretation method of moderngeophysics, with the combination of geology and geophysics, analysis data of geochemistry, comprehensive study the paleoclimate condition, palaeogeomorphology condition, palaeobathymetric analysis, structural evolution characteristic, petroleum geological conditions and reservoir distribution, to cognize the sequence development characteristic, sedimentary facies characteristics, distribution characteristics of beach-bar sand and controlling factor of beach-bar sand development in Chezhen depression. Therefore, the reliable geological foundation for progressive exploration and development could be provided, also the theories number of beach-bar sand study could be increased. There are five mainly achievements and understandings as follow:(1) Based on 3D seismic data, logging data, drilling data, core information,geochemical data, based on the type and feature of unconformity, lake surface recognition, sedimentary characteristics and cycle analysis, Shahejie formation could be divided into 5 level sequence combinations. Through regional sequence stratigraphic correlation, there is more obvious correlation relationship between sequence stratigraphy and beach-bar sand body has been found, and the beach-bar sand body is the most developmental in the process of base-level from decline to rising and in the lower part of the rising hemicycle. Palaeogeomorphology also affects the development of the formation, sand set formation thins in the high place of structure setting and sands set is reduced; in the lower place of structure setting,formation thickness is larger, sand layer is more development, high place is lack of some sand layer.(2) Study the lithologic feature in detail, density distribution feature, the bedding type and biological disturbance combined feature of the second member of Shahejie formation, combine the feature and types of logging curve, and sedimentary structure and lithology on the longitudinal variation characteristics, in detail divide the beach-bar sand bodies into host sand body microfacies, side sand body microfacies,bar microfacies, host beach body microfacies, beach microfacies, establish sedimentary model of the study area. Through the comparison between analysis of single well sedimentary facies and sedimentary profile, establish sedimentary system of the study area of the second member of Shahejie formation. Through spectral processing, waveform classification seismic data, the processing and interpretation of the phase and amplitude, achieve recognition and prediction of thin sand bodies;through the seismic waveform analysis of self-organizing neural networks, establish on behalf of the sequence of typical gradient of the region’s seismic trace shape change, through the instantaneous frequency analysis technology and amplitude ofcomposite property analysis technology, establish forward modeling of sand wedge-shaped body, identify the distribution of the thin layer sand body.(3) Development controlling factor within beach-bar sand body comprises a broad spectrum of analysis which include palaeoclimate condition,paleogeomorphology condition, palaeobathymetric calculation, denuded strata comeback, compaction correction of stratum thickness and etc. in study area. To confirm 30 meter is the boundary between half-deep lake and shallow lake. Also,slope, wave and valley zone represent a good beach-bar sand developing area, and 17 to 30 meter is the good beach-bar sand developing water depth.(4) According to the current development and distribution characteristics of reservoir, combining with sedimentary, sequence and structure distribution and the position In favor of the beach-bar sand body development, analysis suggests that the main control factors of reservoir formation in the study area of second member of Shahejie formation:source fault controls oil-gas migration; near the oil source faults and connected sand body is the place where oil and gas enrichment, the nose structure is the main pointing area of oil and gas migration, and affect the plane distribution regularity of oil and gas; the pros and cons of reservoir and fault configuration determine the reservoir type and longitudinal distribution, comprehensively analyze of geological factors and forming factors, summarize that oil and gas reservoir formation pattern of the study area is the ladder migration, fan-shaped form.