高分辨率层序地层学在川西须家河组砂体分布研究中的应用

陆相地层横向变化大，等时对比困难，而前期岩相古地理编图尺度大，难以满足油气勘探的要求，而且对重点区块高精度储层预测约束不够。为此，以高分辨率层序地层学理论和技术方法为指导，通过基准面旋回结构、叠加样式的沉积动力学分析，结合地表露头、钻井岩心、测井、地震资料的综合研究，将川西上三叠统须家河组划分为5个长期层序、16个中期层序，以地震反射为约束，建立了四川盆地及川西坳陷长、中期基准面旋回层序地层格架。采用层序-岩相古地理编图方法，以长、中期基准面旋回上升、下降相域为单元编制了四川盆地、川西坳陷岩相古地理图。在三维地震区块内，识别出数十个与小层单砂体相当的短期旋回层序，以短期旋回为单元，建立高分辨率层序地层格架；以长、中期层序界面，湖泛面为单元建立地震低频模型，以此为约束进行地震岩性反演；以区域岩相古地理背景为约束，编制短期旋回小层砂体厚度图和沉积微相图，详细讨论了典型小层砂体的纵横向分布与基准面旋回变化的关系，进而预测了该区有利砂岩储层的横向分布

APPLICATION OF HIGH RESOLUTION SEQUENCE STRATIGRAPHY TO RESEARCH OF SANDBODY DISTRIBUTION IN XUJIAHE FORMATION, WEST SICHUAN BASIN

Terrestrial formation is relatively large in lateral variation and difficult in isochronous stratigraphic correlation. In addition, the scale of previous lithofacies paleogeographical mapping is too large to meet the needs of petroleum exploration, and the constraints on high precision reservoir prediction in some major exploration areas are poor. Under the guidance of the theories and methodologies of high resolution sequence stratigraphy, the Upper Triassic Xujiahe Formation in the western Sichuan Basin is divided into 5 long term sequences and 16 middle term sequences through dynamic analysis of base level cycle structure and superimposition pattern and in combination with comprehensive studies of outcrops, cores, logging and seismic data. Taking seismic reflection data as the constraints, sequence stratigraphic frameworks are established for the long term and middle term base level cycles in the Sichuan Basin and the western Sichuan depression. Taking the ascending and descending facies tracts of the long term and middle term base level cycle as mapping units, the lithofacies paleogeography of the Sichuan Basin and the western Sichuan depression are mapped by using the sequence lithofacies paleogeographical methods. Tens of short term cyclic sequences corresponding to sublayer single sandbodies are identified in the 3D seismic survey area and are used for establishing high resolution sequence stratigraphic framework. The long term and middle term sequence boundaries and lake flooding surfaces are used to build low frequency seismic model, which is used as constraint for seismic lithology inversion. The thickness and sedimentary microfacies of short term cyclic sublayer sandbodies are mapped with the regional lithofacies paleogeographical background as constraints. The relationship of the lateral and vertical distributions of typical sublayer sandbodies with the variation of base level cycles is discussed in detail and the lateral distribution of the favorable sandstone reservoirs in the study area are predicted.