Characteristics Of Source-to-sink System And Sand Control Mechanism Of Shahejie Formation In Central And Southern Qikou Depression

The genetic types and structural characteristics of different tectonic units in different tectonic backgrounds of faulted basins are diverse,and the sand-controlling mechanism is complex and different.How to accurately determine the sand control mechanism of different slope and improve the accuracy of sand body prediction has become a major problem in secondary exploration and fine exploration in faulted basins.This paper took the Shahejie Formation in central and southern Qikou Depression of the Bohai Bay Basin as the key research objective.Based on the latest 3D seismic,logging and core data covering the entire work area,guided by the theory of sequence stratigraphy,starting from the theory of source-to-sink system,this paper analyzed the provenance system and depositional system in study area,clarified the provenance supply period,source direction,sediment transport channel,deposition system distribution and source-to-sink system coupling relationship,comprehensively constructed a set of research methods for the source-to-sink system of faulted basins,and summarized the sand control mechanism and improved the success rate of sand prediction.Based on the theory of sequence stratigraphy,the study area is divided into 7 three-level sequences from bottom to top,and four types of stratigraphic superimposition styles including rotation tilt,multi-level deflection,differential settlement and multi-level fault type are established.The SQEs₃³-SQEs₃¹in study area has an obvious pattern of uplifts and depressions.The SQEs₂is reduced in the sedimentary area due to regional unconformities.the SQEs₁^x-SQEs₁^shas slowed down,and the high-thick layer area gradually moves northward.The provenance system of the Shahejie Formation in study area is divided into two types:regional provenance and local provenance.It is pointed out that the entire Shahejie Formation study area is mainly supplied by regional sources(Cangxian Uplift and Chengning Uplift).Local provenances of SQEs₃³-SQEs₂in the basin(Gangxi Uplift,Yangsanmu Uplift,Kongdian Uplift)can supply a large amount of sediment to Qikou main depression,while the supply ability of local provenances in the SQEs₁^x-SQEs₁^sbasin gradually became weakened or even disappeared.Based on paleomorphology and well-seismic data,three types of sediment transport channels,including fault troughs,transition zones and adjustment zones,are identified.It is pointed out that the sediment transport channels in study area have the characteristics of"planar segmented development and vertical differential evolution".Based on the distribution relationship between sand bodies and sediment transport channels,the position and direction of sediment input to slope controlled by the basin margin transition zone,the plane distribution characteristics of sediments controlled by sediment transport channels,and the sand body development mode was controlled by the superimposed pattern of slope strata.Three sand control mechanisms of Shahejie Formation in the central and southern Qikou sag are established.Different types of source sink system sand control models are summarized.Based on the genetic mechanism of different tectonic units,stratigraphic superimposition styles and the characteristics of the source-sink system,the Shahejie Formation in central and southern Qikou Depression is summarized into four source-to-sink system types,and different types of source-to-sink system coupling modes and sand control mechanisms are summarized.Among them,the regional provenance-multi-step fault slope-braid-shaped river delta source-sink system has a sand control mechanism of“transition belt sand transport,fault slope-flat system controlling sand,and adjusting belt sand”;local provenance-multiple Grade flexural slope-braided river delta-type source-sink system has a sand control mechanism of"sand transportation in the same direction fault trough combination,flexural slope-flat control sand,reverse double fault trough sand accumulation";mixture source-differential settlement The slope-braided river delta-type source-sink system has a sand-controlling mechanism of"landform control sand";the regional provenance-rotating tilt slope-fan delta source-sink system has a"steep slope transition zone for sand transport,provenance-landform"Sand control mechanism of"sand control,broken groove bundle sand".