Study on engineering geological characteristics of southwest shale oil based on nuclear magnetic resonance imbibition flooding technology

Low-field nuclear magnetic resonance (LF-NMR) technology plays a growing role in studying reservoirs for oil displacement characteristics. To better explore the reservoir characteristics of Da'anzhai in the Sichuan Province of China, this paper uses LF-NMR imbibition flooding experiments to study the improvement of oil displacement efficiency for shale oil reservoirs in Southwest China by different imbibition flooding technologies. In this article, experiments in scanning electron microscopy, X-ray diffraction analysis, and rock mechanics were conducted to analyze the geological features of the reservoir in the study area. In combination with the test results of the nuclear magnetic resonance method, the field technology has been reformed to improve the oil recovery efficiency. The results show that the Da'anzhai area is mainly composed of interbedded shale and limestone, with a relatively low organic carbon content and low average porosity. The pores shouted are predominantly concentrated in the range of 1–100 nm, and there are micrometer-sized pores. The mineral composition of the area is primarily quartz, dolomite, and calcite, rich in clay minerals. The degree of the development of natural fractures is not high, and the mean coefficient of stress differential in two directions is 0.19. The content of brittle minerals is greater than 50%, meaning that the overall compressibility is good. The results of the stratified T₂ test show that the imbibition efficiency of shale in this area is low. The imbibition efficiency of the three cores is the best in 0–20 mm, and the imbibition efficiency is low in the 40–60-mm section. The optimum imbibition formula 2 has an apparent promoting effect on the imbibition of shale in this area. Based on the optimal formula system of imbibition flooding experiments, the average reservoir volume of reconstruction (SRV) in the Sichuan Basin increased from 39 million cubic meters to 46 million cubic meters. The oil production test went from “seeing boiling oil” to almost 2 tons/day, making a significant breakthrough in “oil production.” As a result, LF-NMR technology is used to investigate the effects of core imbibition and oil displacement. The results can be used as a guide for applying on-site oil production technology transformation, which is of constructive importance for improving production.