鄂尔多斯盆地富县地区长8层段致密砂岩储层特征及充注下限

石油充注下限是致密油成藏研究的基础。鄂尔多斯盆地富县地区长8层段致密砂岩储层微观结构十分复杂，储层微观结构是影响石油充注的关键。利用场发射扫描电镜和CT方法定量研究致密砂岩储层孔隙-喉道特征；采用力学方法、录井分析法以及有效孔喉法综合分析致密储层充注物性下限与充注孔喉下限。研究结果表明，致密储层孔隙大小以纳米和亚微米级为主，孔隙平均半径为1.2 μm，喉道平均半径为0.1 μm，属于细孔-微细喉储层。经计算，长8致密砂岩储层孔隙度充注下限为4.5%，渗透率充注下限为0.04×10-3 μm2，源储界面储层孔喉充注直径下限为15.77 nm，储层内部孔喉充注直径下限为24 nm。综合分析认为油气能充注纳米级孔，根据压实及胶结程度由弱至强，最终石油分别以油珠状、喉道状和薄膜式赋存。 

Reservoir properties and hydrocarbon charging threshold of Chang 8 tight sandstones in Fuxian area,Ordos Basin

Hydrocarbon charging threshold is the basis for tight oil accumulation research. The microstructure of Chang 8 tight sandstone reservoirs in the Fuxian area of Ordos Basin is very complicated, which is a key factor influencing hydrocarbon charging. Field emission scanning electron microscopy (SEM) and CT methods were used to quantitatively study the pore-throat characteristics of tight sandstone reservoirs. Mechanical properties, well logging and effective pore-throat analyses were used to determine the hydrocarbon charging threshold of physical properties and pore-throat characteristics. The results showed that the pore size of tight reservoirs is dominated by nanometer and submicron scale, and the average pore radius is 1.2 μm. The average radius of throat is 0.1 μm, which belongs to micropore-fine throat reservoirs. It was calculated that the charging threshold of porosity of Chang 8 tight sandstone reservoirs is 4.5%, and that of permeability is 0.04×10-3 μm2. The threshold of pore-throat diameter on the source and reservoir interface is 15.77 nm, and that inside reservoir is 24 nm. We integrated that oil and gas might occur in nano-scale pores as oil bead, throat or thin film as compaction and cementation effects became stronger.