Movability of lacustrine shale oil: A case study of Dongying Sag, Jiyang Depression, Bohai Bay Basin

Abstract

Taking the Paleogene Shahejie Formation lacustrine shale in Dongying Sag, Jiyang Depression, Bohai Bay Basin, as an example, this paper makes a systematic study on the properties of shale of lower part of Sha-3 Member (Es3x) and upper part of Sha-4 Member (Es4s), including porosity, compressibility, mechanical properties, oil saturation, gas-oil ratio and oil saturation pressure by lab analysis and well log data of shale cores taken from different depths. On this basis, the movability of shale oil is discussed in terms of formation energy. According to the study results, both the elastic movable oil ratios and the solution gas driving movable oil ratios of Es3x and Es4s increase with the shale burial depth increasing, and both ratios of Es4s are generally higher than that of Es3x at the same depth. Within the depth of 2 800 – 4 000 m, the total movable oil ratio of Es3x varies from 8% to 28%, while the total movable oil ratio of Es4s varies from 9% to 30%. Combining with the profiles of oil saturation and movable oil ratio of shale, a conclusion is made that the shale of Es3x and Es4s deeper than 3 400 m in the study area are favorable objects for shale oil exploration. Key words: lacustrine shale, shale oil, movable oil, porosity, compressibility, saturation pressure