准中4区块中上侏罗统石树沟群储层特征及影响因素

Reservoir characteristics and the impact of Shishugou group of middle-upper Jurassic in block 4 of central Junggar basin

利用铸体薄片、扫描电镜观察、物性测试和压汞实验等方法,分析准中4区块中上侏罗统石树沟群储层的岩石学特征、孔喉特征和物性特征,研究沉积相带与成岩作用对储层物性的影响。结果表明:研究区储层岩屑含量高,成分成熟度较低;岩石类型主要为岩屑砂岩和长石岩屑砂岩,其中岩屑多为火成岩岩屑,矿物之间颗粒支撑,分选中等。储层物性整体上具有中—低孔中—低渗的特征,以粒间溶蚀孔隙为主,喉道多为分选较差的细喉型;局部方解石胶结物较发育,形成特低孔特低渗储层。沉积相带是优质储层发育的先决条件,在强水动力条件下形成曲流河边滩、三角洲分支河道等粗粒砂岩,泥质含量较低,物性较好。酸性流体对早期胶结物的溶蚀是优质储层形成的根本原因,压实作用和后期方解石连晶式胶结是粒间孔隙损失的主要原因,绿泥石黏土膜大量发育而堵塞喉道,造成局部储层渗透率较低。该结果对研究区下一步勘探具有指导意义。

The observation of casting thin section and scanning electron microscope,physical property measurement,mercury injection experiment and other methods were used to analyze petrology characteristics,pore throat characteristics and physical properties of Shishugou group of middle-upper Jurassic in block 4 of central Junggar basin,and study the effects of sedimentary facies belt and diagenesis on reservoir physical property.The results show that reservoir rocks in the study area are mainly lithic sandstone and feldspathic litharenite.Compositional maturity is low,and content of rock debris is high.The type of rock debris is primarily igneous rock debris.Detrital grains are grain-supported,and sorting is medium.Reservoir physical properties have medium-low porosity and permeability in general,and pores are mainly intergranular dissolution pores,and throat is primarily fine-throat with poor sorting.Low porosity and low permeability reservoir formed because of calcite cement developing locally.The sedimentary facies belt is a prerequisite to the development of high quality reservoir.Coarse sandstones formed in strong hydrodynamic conditions,such as meandering river point bar,delta branch channel and so on,which have low shale content and good physical properties.The dissolution of early cement by acidic fluid is the basic reason for the formation of high quality reservoir.Compaction and late calcite intercrystalline cementation are the main reasons for the loss of intergranular pore.Because of excessive chlorite film filling the throats,the reservoir permeability is low locally.The understanding has guided the exploration direction of the research area in the future.