130 / 2022-02-25 00:21:10

孔隙型致密砂岩储层不同岩相可动流体赋存特征及影响因素研究——以松辽盆地三肇凹陷州6区块扶余油层为例

tight sandstone; lithofacies; NMR; movable fluid; Fuyu oil layer; Songliao Basin

Abstract: Movable fluid saturation is an important index to evaluate the seepage characteristics of porous tight sandstone reservoirs. Traditional moving fluid analysis methods usually divide the entire NMR T₂ spectrum into two parts, immovable fluid and movable fluid, based on a single T₂ cutoff, but in this method, there are still moving parts in the immovable fluid, at the same time, the main control factors affecting the fluid saturation of each part and the relationship between them and different lithofacies of tight sandstone are still unclear. In this paper, the Fuyu oil layer in Zhou-6 block of Sanzhao depression, Songliao Basin is taken as the target area, and the full-scale pore throat distribution models of different lithofacies units are obtained by splicing high-pressure mercury intrusion and constant-rate mercury intrusion. The T₂ spectrum is converted to the corresponding pore throat size by using the nonlinear transformation method, and the critical pore throat size of different lithofacies fluid distribution is obtained. Finally, the occurrence characteristics and influencing factors of movable fluid in different lithofacies units are studied. The research shows that there are mainly six lithofacies in Fuyu oil layer , including trough cross bedding fine sandstone facies ( St ), tabular cross-bedding fine sandstone facies ( Sa ), parallel bedding fine sandstone facies ( Sp ) and wavy bedding fine sandstone facies ( Sw ), horizontal bedding siltstone facies ( Fk ) and wavy bedding siltstone facies ( Fi ); according to the T₂ spectral morphology, the lithofacies units are divided into three categories, and the lithofacies of type I ( St, Sa ) are bimodal, with the critical values of 2.66 nm and 6.87 μm ; type II lithofacies ( Sp, Sw ) are high-amplitude- unimodal, with critical values of 2.36 nm and 3.38 μm; type III lithofacies ( Fk, Fi ) are low -amplitude- unimodal, the critical values are 2.55 nm and 1.60 μm;porosity, permeability, average throat radius, pore throat radius ratio, pore mercury saturation, sorting coefficient and mercury injection efficiency are the main controlling factors causing the differences of movable fluid occurrence characteristics in different lithofacies reservoirs. The mercury saturation of throat is one of the important factors affecting the size of partial movable and completely movable fluid saturation. The above studies show that the fluid saturation of pore-type tight sandstone reservoirs with different sizes is mainly manifested by the difference in microscopic pore structure. The establishment of fluid saturation model of tight sandstone reservoir based on lithofacies configuration has guiding significance for quantitative characterization of reservoir heterogeneity and enrichment sweet spot prediction.