多级界面约束下构型对储层非均质性控制作用——以川西沙溪庙组曲流河为例

Controls of Architecture Under the Constraints of a Multi-level Interface on Physical Property Heterogeneities from the Meandering River of the Shaximiao Formation in Western Sichuan

【目的】川西坳陷侏罗系沙溪庙组油气资源潜力大,单砂体内部结构制约了优质储层预测,进而影响了该区天然气富集规律评价。研究区内河道砂体构型界面级次、构型单元及其组合尚不明确,不同级次构型界面约束下的构型单元及其组合如何控制储层非均质性尚缺乏相关认识。【方法】基于野外露头、岩心、测井以及分析测试等资料,在沉积相研究基础上,详细开展了川西沙溪庙组曲流河砂体构型类型及特征研究,探讨了多级界面约束下构型对储层非均质性控制作用。【结果与结论】研究区构型单元划分为边滩构型单元(H_(PB))、河道充填沉积构型单元(H_(CH))、决口扇构型单元(M_(CS))、天然堤构型单元(M_(CL))、废弃河道构型单元(M_(CA))和洪泛平原构型单元(M_(FM))6类,基于构型单元垂向叠置样式,结合垂向序列沉积特征,将构型单元组合划分为均一型组合(Type Ⅰ)、均一+复合型组合(Type Ⅱ)、复合型组合(Type Ⅲ)3大类。研究区中江—回龙地区整体Type I型组合相对最发育,且沙三段整体上Type Ⅰ型组合和Type Ⅱ型组合相对最发育,其储层非均质性相对较弱。基于上述砂体构型类型及特征研究、不同级次构型界面控制下的储层非均质性特征分析以及不同级次构型界面下构型对储层非均质性控制因素探讨,总结了3~5级界面约束下构型对储层非均质性的控制模式。其中5级构型界面控制下的储层平面非均质性受控于基准面上升和构造沉降;4级构型界面控制下的储层层间非均质性受控于地形坡度和侵蚀作用;3级构型界面控制下的储层层内非均质性受控于水动力条件、河道弯度、河道迁移程度、沉积载荷、流量及成岩作用。

[Objective]There is large potential of oil and gas resource from the Jurassic Shaximiao Formation of the eastern slope in the Western Sichuan Depression,and the internal structure of the single sandbodies restrict the pre⁃diction of high-quality reservoirs,and consequently affects the evaluation of the natural gas enrichment characteris⁃tics in this area.The order of the architecture boundary,architecture-element,and architecture-element assemblies in the study area are not yet clear.There is a lack of relevant understanding of how the architecture-elements and their assemblies control the reservoir heterogeneity from the different architecture boundary levels.[Methods]In this study,the types of sedimentary facies were determined to provide the foundation for the study of the sandbody archi⁃tecture.Based on the data of field outcrops,cores,logs,and experimental measured analysis,detailed research on the type and characteristics of the sandbody architecture of the meandering river from the Shaximiao Formation of Western Sichuan Depression was carried out,and the effect of sandbody architecture on the reservoir heterogeneity under the constraints of multilevel architecture boundary was discussed.[Results and Conclusions]The architecture-elements in the study area were divided into H_(PB),H_(CH),M_(CS),M_(CL),M_(CA),and M_(FM).Based on the vertical stacking pattern of architecture units and the sedimentary characteristics of vertical sequence,the architectureelement assemblies are divided into three types,including homogeneous assemblage(Type Ⅰ),homogeneous+compound(Type Ⅱ),and compound assemblage(Type Ⅲ).Type Ⅰ assemblage mainly occurs in the Zhongjiang-Huilong area of the study area,and the Type Ⅰ assemblage and Type Ⅱ assemblage mainly occur in the Third member of Shaximiao Formation,and the reservoir heterogeneity is relatively weak.Based on the above research on the types and characteristics of sandbody architecture,the analysis on the characteristics of reservoir heterogeneity under the control of different levels of architecture boundary,and the discussion of the controlling factors that sandbody architecture impact on the reservoir heterogeneity under different levels of architecture boundaries,the model of controlling the reservoir heterogeneity under the architecture boundary constraints of 3~5 levels of architecture is established.The reservoir plane heterogeneity is controlled by the 5 level'architecture boundary,and the reservoir heterogeneity under the 5 level'architecture boundary is controlled by the rising of based-level and structure subsid⁃ence.The reservoir inter-layer heterogeneity is controlled by the 4 level'architecture boundary,and the reser⁃voir heterogeneity under the 4 level'architecture boundary is controlled by the slope and erosion.The reservoir intralayer heterogeneity is controlled by the 3 level'architecture boundary,and the reservoir heterogeneity under the 3 level'architecture boundary is controlled by the hydrodynamic condition,channel sinuosity,degree of channel migration,deposited load,discharge,and diagenesis.