鄂尔多斯盆地临兴中区块上古生界盒8段储层发育控制因素

Research on controlling factors of reservoir development in Upper Paleozoic He 8 Member in Linxing Middle block,Ordos basin

通过分析岩心、钻测井及地球化学测试资料,结合大量岩石、铸体薄片及扫描电镜观察研究,明确了鄂尔多斯盆地临兴中区块上古生界盒8段的沉积特征、储层发育特征和储层物性主控因素。研究区盒8段发育辫状河三角洲平原沉积体系,主要包括分流河道及分流间湾微相,其中分流河道以心滩沉积为主,为研究区的骨架砂体,河道侧向迁移、改道频繁,砂体间相互冲刷、切割及叠置,垂向上可形成20 m以上的巨厚砂体;由于分流河道位置多变,同时对下伏沉积物有强烈冲刷作用,分流间湾有时保存不完整或不太发育。研究区盒8段储层砂岩类型多为长石岩屑砂岩和岩屑长石砂岩,岩屑砂岩次之;储层储集空间类型以剩余原生粒间孔、粒间溶孔、粒内溶孔为主;储层物性表现为低孔、特低渗特征;储层孔隙结构可划分为3类,主要为Ⅱ类、Ⅲ类储层,储集空间以中小孔隙为主,排驱压力较高。研究区盒8段储层物性主控因素表现为:物源提供了储层的物质基础,沉积时期物源主要来自盆地北部,具有东西分带的特征;沉积体系决定了砂体类型及发育规模,分流河道主河道砂体和心滩沉积厚度大于15 m,为最有利储层发育区;成岩阶段处于中成岩阶段A期,压实作用及各类胶结作用是本区储层致密化的主要原因,而溶蚀作用是本区最主要的建设性成岩作用,是改善储层致密性的关键。

This paper, through analysis on the data of core , drilling and logging , geochemical te s ts , has de-fined reservoir accumulation characteristics, reservoir development characteristics, and reservoir main con-trolling factors of Upper Paleozoic He 8 Member in Linxing Middle block , Ordos basin , while combining with rock observation, cast thin-section observation and scanning electron microscope observation. The braided river delta plain sedimentary system developed in He 8 Member in the study area, mainly including distributary channels and interdistributary bay micro-phase, in which the distributary channels are mainly mid channel bar deposits as the skeleton sand body in the study area. With lateral migration and frequent diversion of the river channel, mutual scouring, cutting and stacking between sand bodies, thick sand bodies with a thickness up to 20 m can be formed vertically; Due to the changing location of the distributa-ry channels and the strong erosion of the underlying sediments, the distributary bays are sometimes incom-plete or not well developed. Most of the reservoir sandstones in He 8 Member of the study area are lithic arkose and lithic feldspathic sandstone, followed by lithic sandstone. The main types of reservoir space are residual primary intergranular pores, intergranular dissolved pores and intragranular dissolved pores. The reservoir physical properties are characterized by low porosity and extra-low permeability. The pore struc-ture of reservoirs can be divided into three types, and type II and HI reservoirs constitute the main part, where the reservoir spaces are dominated by small and medium-sized reservoir pores, with high displace-ment pressure. The main controlling factors of reservoir physical property in He 8 Member of the study ar-ea are as follows： tte source provides tte material foundation of tte reservoir; during tte sedimentary peri-od, sediments are mainly from the northern part of the basin, which has the characteristics of the east and the west zoning. The sedimentary system determines the type and development scale of the sand body, and sedimentary thickness of the main river channel of the distributary channel and mid channel bar is over 15 m, marking them the most favorable development zone of reservoirs. The diagenetic stage of the study area belongs to stage A of middle diagenesis phase, and the compaction and various types of cementation are the main reasons for the compaction of reservoirs in this area. However, dissolution is the most important constructive diagenesis in this area and is the key to improving the density of reservoirs.