Abstract:

Diagenesis controls the development of the storage space of oolitic banks, and their different diagenetic sequences determine the physical properties of the final reservoir. The Cambrian Zhangxia Formation at Xiaweidian occurs mainly in the oolitic bank facies in the carbonate platforms. In this study, based on outcrop descriptions, thin section observations and XRD, we discuss the major diagenetic types and sequence, and exploration prospect of the Zhangxia Formation. We conclude that: (1) Major diagenetic processes that affect the reservoir quality of oolitic bank include compaction, pressure dissolution, cementation and dolomitization. Silicification occurs mainly as silicide around the ooids; (2) Dolomitization of ooids mainly occurs in the syngenetic diagenetic stage, dolomite intercrystal pores are the main reservoir space of the local oolitic bank. The eogenetic and telogenetic diagenetic stage is mainly based on the compaction and pressure dissolution of the oolitic bank, resulting in a sharp porosity drop; (3) Migration and storage complex system, composed of the stylolite and dolomite intercrystal pores, is a possible storage space in the local oolitic bank. In the provision that the hydrocarbon supplying ability of the Proterozoic source rocks is confirmed, the Zhangxia Formation represents a new potential sequence for exploration, and warrants further investigation.

Key words: Xiaweidian area, Zhangxia Formation, oolitic bank, diagenesis