Fracture network fracturing combined with oil–water infiltration and replacement is an effective approach to develop tight sandstone reservoirs. How to further improve oil recovery based on imbibition is a problem encountered during production. In this study, the core of the CHANG-7 tight sandstone reservoir in the Changqing oilfield of the China National Petroleum Corporation (CNPC) is studied. Combined with the newly designed core self-imbibition experiment, the mechanisms of salinity action are studied, and the influence of salinity on the process of imbibition oil recovery is quantitatively characterized. Research results show that the influence of salinity on the imbibition process of tight sandstone reservoirs takes place mainly through two ways; one is to reduce the oil–water interfacial tension, and the other is to construct an osmotic pressure displacement model. The salinity has significant influences on interfacial tension. The interfacial tension of low-salinity brine is only 1/5 of that of distilled water, but in the presence of high-efficiency surfactants, the influence of the salinity on the interfacial tension can be ignored; the greater the difference in salt concentration, the higher the core permeability and the greater the influence of salinity on the process of imbibition and oil recovery in tight sandstone reservoirs. At the initial stage of imbibition, the effect of salinity is less important than that of capillary force. On the contrary, the effect of salinity is much more important than that of capillary force in the middle of imbibition, and the imbibition curve shows a downward trend. At the later stage of imbibition, the fluid tends toward imbibition equilibrium, and the effects of capillary force and salinity are not obvious.

The Chang 2 bottom water reservoir area in the western part of northern Shaanxi constitutes one of the key oil-producing regions within the Ordos Basin. A principal reservoir here is the Triassic Yanchang Formation’s Chang 2 reservoir, which is characterized by favorable physical properties, dynamic edge and bottom water activity, and a high geothermal gradient. This study employs the STARS module of the CMG reservoir numerical simulation software to model water intake and heat recovery processes in the target region. It analyzes the heat recovery rate and efficiency of three water production methods—direct water extraction, four-injection–one-production, and one-injection–four-production—under varying injection pressures. The results indicate that direct water extraction from the bottom water reservoir is challenging. However, the annual heat recovery per well for the four-injection–one-production and one-injection–four-production methods equates to a standard coal production ranging between 190 and 420 tons, suggesting that there is significant potential for water injection and heat recovery in the Chang 2 reservoir in the western part of northern Shaanxi.