Characteristics and Evaluation of the Shale Oil Reservoir in Upper Es³ Inter Salt in Liutun Sag

Shale intercalations in salt deposits of the upper part of the third member of the Shahejie (沙河街) Formation (Es³) in the Liutun (柳屯) sag have industrial oil and gas potential. This article classifies and evaluates lithology, pore systems, porosity, permeability and pore characteristics using core logs, XRD, SEM, lab and log porosity data of shale reservoirs in the salt formation. The lithology of these reservoirs is complex as parts of complex salt rhythms composed of clastic, carbonate and evaporitic rocks. Their rigid minerals contents and total organic carbon are high, the organic type is good, and the maturity of organic matter ranges from medium to low. There are strong overpressures and natural hydraulic fractures. Organic matter pores and matrix-related shale pores provide an appreciable part of the permeability. Different methods of measurement, sonic logging and equivalent cycle counting-point are used to evaluate the different types of porosity and permeability. A preliminary evaluation of shale permeability has been made by using fracture data from cores and image logging, and it is considered that the organic nets composed of organic matter pores generated in the maturation stage of shale have greatly increased oil permeability. On the above basis, this article proposes classification criteria for the upper Es³ inter-salt shale oil reservoirs to provide a foundation for evaluating other shale oil reservoirs in this area.