Abstract: The interlayers developed in the reservoir restrict the distribution of remaining oil. In view of the difficulty in enhancing recovery efficiency of remaining oil by gas injection after long-term water-flooding development in E₃¹ reservoir of Gasikule Oilfield, Qaidam Basin, in the study case of Ⅳ-3 to Ⅳ-5 sublayers in E₃¹ reservoir, Gasikule Oilfield, a comprehensive study was conducted on core, logging, test and analysis to identify the types, characteristics and genesis of interlayers, establish the standards for interlayer identification, and characterize spatial distribution characteristics of interlayer on these standards. It was found in the study that argillaceous and calcareous interlayers were mainly developed in Gasikule E₃¹ reservoir, with argillaceous interlayer dominated, whose genesis was mainly controlled by high-frequency cycles, and calcareous interlayer was distributed relatively less and mostly formed by cementation. Based on the analysis of stratigraphic architecture and stratigraphic texture, the interlayer of Gasikule E₃¹ reservoir can be divided into three levels: interlayer between sublayers, interlayer between single sandbodies and interlayer in single sandbody. A quantitative identification standard of argillaceous interlayer and calcareous interlayer was established based on the normalization of log curves of GR, SP, AC and R_LLD. The interlayer between sublayers was thick, high in continuity, and basically distributed in the whole area; the interlayer between single sandbodies was poor in continuity and continuously distributed in some places; the interlayer in single sandbody was sporadically distributed, with the thinnest thickness. The study results provide a certain geological basis for gas-flooding development of Gasikule E₃¹ reservoir.

Key words: interlayer, stratigraphic texture analysis, logging identification, distribution law, Lower Ganchaigou Formation, Gasikule Oilfield