Sedimentary environment and sedimentary cycles of the Pabde Formation in the Ab-Timur oil field (wells no. 14 and no.19)

In this study, the Pabde Formation has been investigated in wells No. 14 and No. 19 of the Ab-Timur oil field to reconstruct the sedimentary environment of the deposits of this Formation and its sedimentary cycles. The data of this research have been obtained from the study of oil well reports, macroscopic observations on drilling rock fragments, and microscopic analysis of their thin sections. Library findings and observations showed that it is possible to divide the Pabde Formation succession in oil well no. 14 of the Ab-Timur oil field into two stratigraphic units and in oil well no.19 into three stratigraphic units, based on the ratio between the limestone and the shale layers and their fossil content. The data from the study of microscopic thin sections and statistical calculations showed that the deposits of this Formation could be divided into mudstone, wackestone, packstone, laminar, and sparse packstone microfacies group and a terrigenous facies group. Statistical calculations data and comparison of the microfacies group with standard facies models showed that Pabde sediment occurred in the middle to the outer portion of a carbonate platform in this oil basin. The laminar microfacies group was deposited in the middle part and the other microfacies groups were deposited in the outer part of the platform. The microfacies changes in the succession show that the Pabde Formation can be divided into 8 small-scale sedimentary cycles, 3 medium-scale sedimentary cycles, and a large-scale sedimentary cycle and into 6 small-scale sedimentary cycles, 2 medium-scale sedimentary cycles (each of them belongs to a large-scale sedimentation cycle) in oil-well no.14, and in oil-well no. 19, respectively.