Calculation of oil saturation in clay-rich shale reservoirs: A case study of Qing 1 Member of Cretaceous Qingshankou Formation in Gulong Sag, Songliao Basin, NE China

The targeted reservoir, which is referred as the first member of Cretaceous Qingshankou Formation in Gulong Sag, Songliao Basin, NE China, is characterized by the enrichment of clay and lamellation fractures. Aiming at the technical chal-lenge of determining oil saturation of such reservoir, nano-pores were accurately described and located through focused ion beam scanning electron microscopy and quantitative evaluation of minerals by scanning electron microscopy based on Simandoux model, to construct a 4D digital core frame. Electrical parameters of the shale reservoir were determined by finite element simulation, and the oil saturation calculation method suitable for shale was proposed. Comparison between the results from this method with that from real core test and 2D nuclear magnetic log shows that the absolute errors meet the requirements of the current reserve specification in China for clay-rich shale reservoir. Comparison analysis of multiple wells shows that the oil saturation values calculated by this method of several points vertically in single wells and multiple wells on the plane are in agreement with the test results of core samples and the regional deposition pattern, proving the accuracy and applicability of the method model.