砂体构型成因模式及其对物性的控制作用--以苏里格气田西区二叠系盒8段为例

Genetic models of sand body architectures and their control on physical properties:taking the Lower Shihezi Member 8 of Permian in west area of Sulige gas field as an example

砂体构型研究对致密储层储集性能的评价和预测具有重要意义。以苏里格气田西区盒8段辫状河三角洲平原沉积砂体为研究对象,综合利用岩心、测井、薄片等资料,分析不同构型砂体沉积-成岩过程的差异性及对物性的控制作用。根据砂体空间展布特征,确定堆叠型、侧接型和孤立型等3种砂体类型,再结合测井曲线(GR)形态,进一步将堆叠型和孤立型分别细分为箱状堆叠型、钟状堆叠型、复合堆叠型和箱状孤立型、钟状孤立型、指状孤立型。受沉积成岩作用的影响,不同砂体构型具有不同的物性特征。心滩及河道中央以发育箱状堆叠型、复合堆叠型砂体为主,砂体垂向厚度大,侧向延伸远;沉积水动力较强,粒度较粗,杂基含量低,原始孔隙发育;石英及刚性碎屑发育,抗压实能力强,有利于原始孔隙保存,同时为有机酸流体流动提供空间,有利于次生溶孔的发育,因此物性较好。向河道边缘过渡,钟状砂体逐渐发育,砂岩粒度变细,泥岩夹层逐渐发育,物性变差。河道边缘发育孤立型漫溢砂体,砂体厚度薄,侧向延伸短;粒度较细,与泥岩呈互层接触,原始孔隙欠发育;受周围泥岩因压实作用排出的流体影响,易形成碳酸盐胶结,导致储层致密。

The study of sand body architectures is of great significance to the evaluation and prediction of tight reservoir performance.In this paper,sand bodies of the braided river delta plain of the Lower Shihezi Member 8 in the west area of Sulige gas field are taken as the research object,and the differences of sedimentation-diagenesis process of sand bodies with different architectures and their control on physical properties are analyzed by comprehensive use of core,logging and thin section data.According to the spatial distribution characteristics of sand bodies,three types of sand bodies are identified,including stacked type,side connected type and isolated type.Combined with logging curve morphology,the stacked sand bodies are further subdivided into box-shaped stacked type,bell-shaped stacked type and composite stacked type,and the isolated sand bodies into box-shaped isolated type,bell-shaped isolated type and finger-shaped isolated type.Due to the influence of sedimentation-diagenesis,different sand bodies have different physical properties.In the middle of the channel and channel bar,the box-shaped and composite stacked sand bodies are mainly developed,with large vertical thickness and long lateral extensional distance.The hydrodynamic force of these was strong,therefore the particle size is relatively coarse,the content of matrix is low,and the original pores are developed.The quartz and rigid debris of these are developed,therefore the anti-compaction ability is strong,which is conducive to the preservation of original pores that provides space for the flow of organic acid fluid,which is conducive to the development of secondary dissolved pores,so they have good physical properties.In the transitional zone to the channel edge,bell-shaped sand body gradually develops,the grain size becomes smaller,mudstone intercalation develops gradually,and physical properties become poor.Isolated overflow sand body is developed at the edge of channel,with small thickness and short lateral extension distance.It has fine grain size,interbedded contact with mudstone and has undeveloped original pores.It is easy to be affected by fluid discharged from surrounding mudstone by compaction,which form carbonate cementation resulting in tight reservoir.