致密砂岩储层微观孔喉结构非均质性对水驱油渗流特征的影响OA

To investigate the influence of microscopic pore-throat structure heterogeneity on fluid mobility and water-flooding flow characteristics in tight sandstone reservoirs,13 samples from Chang 7 Member of Yanchang Forma-tion in Dingbian area of Ordos Basin are selected.High-pressure mercury injection and nuclear magnetic resonance are used to quantitatively characterize the heterogeneity and fluid mobility at different pore-throat scales.High-tem-perature and high-pressure microscopic visualization water flooding experiment is designed and conducted to clarify flow characteristics and their controlling factors.The results indicate that pore-throat structures of tight sandstone reservoirs in studied area can be classified into 4 types(Ⅰ-Ⅳ),with corresponding heterogeneity gradually increas-ing.Oil-water flow paths progressively change from uniform and network displacement to finger-network and finger displacement,while fluid mobility and oil displacement efficiency decrease sequentially.Full pore-throat size distri-bution exhibits multi-fractal characteristics.Based on fractal inflection points,the pore-throat space can be divided into large,medium and small pore throats,with corresponding fractal dimensions decreasing sequentially.Among them,medium pore throats serve as the dominant space for movable fluids.Microscopic pore-throat structure hetero-geneity is a key factor restricting reservoir fluid mobility and oil displacement efficiency,controlling the fluid occur-rence morphology,flow pathways,and remaining oil distribution.Furthermore,an increase in clay mineral content exacerbates pore-throat structure heterogeneity,reduces reservoir physical properties and fluid mobility,leading to continuous distribution of remaining oil and a decrease in oil displacement efficiency.The research can serve as an important basis for the classification,evaluation and water injection development of tight oil reservoirs in this area.