Experimental investigation of spontaneous imbibition in tight sandstone reservoirs

Based on field conducts, it is found that a lower flowback rate results in a higher oil recovery in a tight sandstone reservoir. Spontaneous imbibition, as a main mechanism of oil production increment for this phenomenon, has been paid more and more attention. The aim of this study is to explain the spontaneous imbibition in tight sandstone reservoirs, find the primary factors, and provide suggestions and guidance for the field operations. This paper performs the study using tight sandstone core samples, coming from a block in Ordos Basin. First, different phenomena were observed through core imbibition experiments. The phenomena were explained in depth by mercury intrusion tests, casting sheet experiments and fractal dimension. Then, a completely randomized designed experiment was proposed. Stabilization time of spontaneous imbibition was defined for the first time. The effects of permeability, salinity, viscosity, and interfacial tension on the recovery factor (RF) and stabilization time were discussed. The feasibility of the experimental approach was verified. Finally, the primary factors affecting the RF and the stabilization time were obtained based on the principal component analysis (PCA). And some suggestions were proposed to provide guidance for the field operations. The research results of this paper bring a better comprehensive understanding of spontaneous imbibition in tight sandstone reservoirs, providing significant guidance and suggestions for the field promotion of imbibition oil displacement.