鄂尔多斯盆地杭锦旗地区二叠系下石盒子组岩屑发育特征及其对储层物性的影响

鄂尔多斯盆地杭锦旗地区具有良好的致密气勘探潜力，下石盒子组是杭锦旗地区的主力产气层段。储层岩石类型以岩屑砂岩和岩屑质石英砂岩为主。根据偏光显微镜下铸体薄片观察以及扫描电镜、高压压汞、粘土矿物X-衍射、阴极发光等分析测试手段的应用，结合相关孔渗数据对鄂尔多斯盆地北部杭锦旗地区下石盒子组储层的岩石学特征及储层物性特征进行了研究，明确了岩屑颗粒的发育特征及其对储层物性的影响。结果表明：下石盒子组储层粒度较粗，主要为粗粒及中-粗粒砂岩；岩屑平均含量高达40%。研究区储层埋藏较深，成岩作用改造强烈，压实作用强，原生孔隙绝大部分被改造充填，次生孔隙为主要的储集空间。储层岩屑类型发育多样，根据岩屑对储层物性的影响，将其整体划分为减孔型岩屑、增孔型岩屑、保孔型岩屑3类。减孔型岩屑较发育会使粒间次生溶孔大量减少且自身难以溶蚀，因而破坏储层的物性，其中以高含量的千枚岩岩屑对储层物性影响最为显著；增孔型岩屑的发育则对储层物性有着明显的改善效应，其可以保存部分粒间孔，还易发生内部溶蚀，改善储层物性，其中以高含量的变质石英岩屑对储层物性影响最为显著；保孔型岩屑本身抗压实能力较强且多数较难溶蚀，可以保护原有孔隙却不能通过自身溶蚀改善储层物性，通常与增孔类岩屑同时发育，该类岩屑与物性呈间接性正相关关系。

Characteristics of detritus development in the Permian lower Shihezi Formation in Hangjinqi area and its influence on reservoir physical properties

Hangjinqi area has great potential for tight gas exploration in Ordos Basin and the Lower Shihezi Formation is the major gas pay zone in the area.The reservoir rocks are mainly composed of lithic sandstones and lithic quartz sandstones.Based on the observation of cast thin section and the analyses of the SEM images,high pressure mercury injection,X-ray diffraction of clay minerals and cathodoluminescence,and combining with the relevant porosity and permeability data,we studied the petrological characteristics and physical properties of reservoirs in the Lower Shihezi Formation in Hangjinqi area of northern Ordos Basin and identified the developmental features of detrital grains and their influence on reservoir physical properties.The following results were obtained.The Lower Shihezi Formation reservoir is mainly composed of medium-coarse sandstones characterized by coarse grain size,with an average content of detritus as high as 40%.The reservoir of the study area is deeply buried,and experienced strong diagenesis and compaction later,leading to the filling of most primary pores and the secondary pores acting as the main reservoir space.The reservoir detritus is diversified in types.According to the influence of detritus on reservoir physical properties,the detritus as a whole can be divided into three types,namelypore reducing,pore increasing and pore retaining.The growth of pore reducing detritus leads to massive reduction of intergranular secondary solution pores and it is uneasy for these detritus to dissolve,resulting in the destruction of reservoir physical properties.Among other,a high content of phyllite detritus plays the most significant role in destroying the reservoir quality.While the growth of pore increasing detritus can function to reserve part of the intergranular pores and it is easy for the detritus to dissolve inside,so being of great help for improving the reservoir physical properties.A high content of metaquartzites is the most important factor for this improvement.Besides,the pore retaining detritus usually develops synchronously with the pore increasing one;it's strong in nature in resisting compaction and most of them is difficult to dissolve.Therefore,this detritus can protect the original pores,but could not improve the reservoir physical properties by self-dissolution,and is in indirect positive correlation with physical properties.