Sedimentary Characteristics and Distribution Law of Sandbodies of the First Member of Liushagang Formation of Paleogene of A Well Field in Weixinan Depression

Key words: 
• Weixinan Depression /
• the first Member of Liushagang Formation /
• sublacustrine fan /
• seismic attribution /
• distribution law /
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Abstract:  Large scale glutenite was developed in the sedimentary period of the lower submember of first Member of Liushagang Formation of Paleogene in A well field of Weixinan Depression. Core and analysis and test data l suggest that the sandbody developed abundant sedimentary structure of Bouma cycle, erosion and loading, and the deformation structure and has the type of grain size accumulation curve of uphill arched "1 segment" pattern and line "1 segment" pattern. In vertical section, characterized by superposition of several positive cycles with the sedimentary structure of erosion and loading in the bottom, phase sequence displays the positive sequence as a whole. Sedimentary characteristics showed that the glutenite was sublacustrine fan. 3 stages of sublacustrine fan deposits have been recognized according to the seismic reflection characteristics and the patterns of superposition of verstical formation. In each stage the thickness of sand body of sublacustrine fan is well related to the seismic attribution of average peak amplitude, energy half time and instantaneous frequency. Under the constraint of high resolution sequence stratigraphic framework, combined with well drilling, logging and analysis of seismic attribution, each stage of sublacustrine fan is characterized by contstant migration and wiggle in twodimensional system, and superimposed development in the vertical evolution. The episodic activity of No.5 fault as a result of the influence of No. 0 fault and No.3 fault, led to the transformation of accommatation space. So, the unbalanced transformation of accommatation space constrainted by structure activity is the main factor controlling the distribution of sand body of sublacustrine fan of the first Member of Liushagang Formation.