Many sets of calcareous interlayers are present in the Shawan Formation in the Chunfeng oilfield, which leads to scattered residual oil that is difficult to extract.

Observations of core samples and thin sections, analyses of trace element compositions and interpretations of logging data were used to identify the calcareous interlayers and identify their possible origin.

First, the petrologic characteristics of the calcareous interlayers were identified; then, we developed a quantitative function for identifying the calcareous interlayers based on well log data. Finally, the possible origin of these calcareous interlayers was identified based on these findings.

The results show that the quantitative function has a high accuracy of 91.8% and average uranium content of calcareous interlayers can reach as high as 27×10^-6, indicating that the quantitative identification function provided accurate identification of the calcareous interlayers, and highly radioactive uranium is one explanation for the origin of the calcium cementation.