玛南斜坡区风城组致密油藏储集层特征及控制因素

通过岩石薄片鉴定、X射线衍射分析、高压压汞测试等手段，研究了准噶尔盆地玛湖凹陷玛南斜坡区二叠系风城组二段致密油藏储集层的沉积环境、岩相类型、孔隙类型以及孔隙结构。结果表明，研究区风城组为封闭咸化湖盆沉积，由陆源碎屑、火山碎屑和自生矿物按不同比例混积形成的储集层，按照沉积构造、岩石组分和粒度，将储集层岩相划分为块状石灰质中—细砂岩相、块状白云质细砂岩相、纹层状白云质粉砂岩相和纹层状白云质泥岩相4类优势储集岩相；储集层孔隙类型有残余粒间孔、火山碎屑溶孔、矿物晶间孔、裂缝等，不同类型储集层孔隙直径和喉道半径差异较大。优势储集岩相是优质储集层形成的基础，溶蚀作用决定次生孔隙的形成，火山灰脱玻化形成长英质胶结物加剧储集层致密化，裂缝发育是油气高产的必要条件。研究区块状石灰质中—细砂岩相和块状白云质细砂岩相压实作用相对较弱，细粒火山灰含量相对较低，物性和孔隙结构较好，是较优质储集层。

Characteristics and Controlling Factors of Tight Oil Reservoirs of Fengcheng Formation in Southern Slope of Mahu Sag

By means of thin section identification，X-ray diffraction analysis，physical property analysis，and high-pressure mercury intrusion testing，the depositional environment，lithofacies，pore type and pore structure of the tight oil reservoirs in the second member of the Permian Fengcheng formation in the southern slope of Mahu sag in Junggar basin were studied. The results show that the Fengcheng formation in the study area was deposited in a closed saline lake basin，and the reservoirs of the Fengcheng formation are composed of terrigenous clasts，pyroclastics and authigenic minerals in different proportions. According to sedimentary structure，mineral composition and particle size，the reservoirs of the Fengcheng formation are divided into four types of dominant lithofacies，that is，massive calcareous medium-fine sandstone facies，massive dolomitic fine sandstone facies，lamellar dolomitic siltstone facies，and lamellar dolomitic mudstone facies. The pore types of the reservoirs include residual intergranular pores，pyroclastic dissolved pores，mineral intercrystalline pores and fractures，which are different in pore diameters and throat radii. The type of lithofacies is the basis for the formation of high-quality reservoirs，the dissolution determines the formation of secondary pores，the felsic cements resulted from devitrification of volcanic ash aggravate reservoir densification，and developed fractures are necessary for high oil and gas production. The massive calcareous medium-fine sandstone facies and massive dolomitic fine sandstone facies show relatively weak compaction，relatively low contents of fine-grained volcanic ash，and relatively better physical properties and pore structures，indicating high-quality reservoirs.