鄂尔多斯盆地苏里格气田苏6区块盒8段致密砂岩储层微观孔隙结构特征及其意义

应用铸体薄片、扫描电镜、三维CT扫描、高压压汞和恒速压汞等方法，对苏里格气田苏6区块盒8段致密砂岩储层的微观孔隙结构特征进行定量表征，探讨孔隙结构差异性成因，进而优选出反映致密砂岩微观孔隙结构特征的储层评价参数。结果表明:储层孔隙类型主要为(颗粒、胶结物)溶孔、黏土矿物晶间孔及少量残余粒间孔；不同渗透率的储层孔隙半径差别不明显，但喉道半径分布差异较大，储层越致密，喉道半径分布范围越小、小喉道所占比例越高，喉道占有效储集空间的比例也越高；中粗粒岩屑石英砂岩和中粗粒岩屑砂岩结构成熟度高、原始孔隙度高、溶蚀作用强烈，溶蚀孔隙所占比高，形成的半径大于1μm的孔喉含量显著增加；细粒(长石)岩屑砂岩分选差、原始孔隙度低，溶蚀作用弱，孔隙类型主要为黏土矿物晶间孔，形成的孔喉主要为半径小于1μm的孔喉；主流喉道半径对储层渗流能力起主要控制作用，并且可以很好地反映储层的孔喉分布、有效储集空间及非均质性等微观孔隙结构特征，应当作为致密砂岩储层重要的储层评价参数。

Characteristics and Significance of Microscopic Pore Structure in Tight Sandstone Reservoir of the 8th Member of Lower Shihezi Formation in the Su6 Area of Sulige Gasfield

Microscopic pore structure characteristics of tight sandstone reservoir of the8^th member of Lower Shihezi Formation in the Su6 area of Sulige Gasfield was quantitatively analyzed by means of casting thin sections,scanning electron microscope,3D X-ray computed tomography,high pressure mercury injection,constant-rate mercury penetration.The purpose was to discuss the causes of differences of microscopic pore structures,and further to screen evaluation parameter which could reflect the microscopic pore structure characteristics of tight sandstone reservoir.The results are as follows.Reservoir space types include (grains and cements) dissolved pores,clay-mineral intercrystalline pores and primary remained intergranular pores.Reservoirs with different permeability have less differences in pore radius but obvious differences in throat radius.The reservoir is more tight with smaller range and greater proportion of fine pore-throat.The throat also accounted for higher proportion of effective reservoir space.The medium-to-coarse grained lithic sandstones and medium-to-coarse grained lithic quartz sandstones have higher textural maturity and primary porosity,which have experienced strong dissolution.The dissolved pores are large proportion of total pore content,and the pore-throat radius content increases significantly,which are more than 1μm in the two types of medium-to-coarse grained sandstones.The small grained (feldspar) lithic sandstones have lower textural maturity and primary porosity,which have experienced weak dissolution.The pore types in the small grained sandstones are mainly clay-mineral inter-crystalline pores,and the pore-throat radius in which is less than 0.1μm.Mainstream throat radius plays the main controlling effect on reservoir permeability,and can well reflect the microscopic pore structure,such as reservoir pore-throat distribution,effective reservoir space and heterogeneity.In conclusion,mainstream throat radius should be an important reservoir evaluation parameter for the tight sandstone reservoir.