A saturation model of lacustrine shale oil considering the influence of organic matter: A case study of the first member of the Cretaceous Qingshankou Formation of Changling Sag in southern Songliao Basin, NE China

Taking the shale oil of the first member of the Cretaceous Qingshankou Formation of Changling Sag in southern Songliao Basin as an example, this paper establishes a saturation model of lacustrine shale oil considering the influence of organic matter on clay-bound water conductivity. Based on the fluid characterization results of sealed samples and two-dimensional nuclear magnetic resonance, the differential influence of organic matter on clay-bound water conductivity was quantitatively revealed, and the conductivity mechanism and rock-electrical relationships of lacustrine shale were systematically analyzed. The results show that there are two conductive networks for lacustrine shales, i.e. the matrix free water and the clay-bound water. The bound water cementation index m sh was introduced to reflect the impact of organic matter on clay-bound water conductivity, and it is positively correlated with the effective porosity. When there is sufficient rigid framework support and well-developed pores, organic matter is more likely to fill or adsorb onto clay interlayers. This reduces the ion exchange capacity of the electrical double layer, leading to an increase in m sh and a decrease in the conductivity of clay-bound water. The overall conductivity of shale is controlled by the clay-bound water conductivity, and the relative contributions of the mentioned two conductive networks to formation conductivity are affected by the effective porosity and m sh . The larger the effective porosity and m sh , the more the contribution of the matrix free water to formation conductivity. According to the experimental results, the proposed saturation model yields a significantly higher interpretation accuracy in oil saturation than the Archie model and the Total-shale model.