Effect of Diagenesis on Reservoir Distribution in a Sequence Stratigraphic Framework: Evidence From the Changxing Formation (Permian) in Tieshan District of Northeastern Sichuan, China

Abstract

Abstract

The marine carbonate reef reservoir in Changxing Formation of the Upper Permian is a major target of gas exploration in Sichuan Basin, southwestern China. By integrating diagenesis and sequence stratigraphy, the effect of sedimentary-diagenetic reformation on reservoir quality and distribution was investigated with in a sequence stratigraphic framework. Based on the petrological characteristics, sedimentary microfacies and logs analysis, 2 third-order sequences and 6 system tracts are distinguished in the Changxing Formation, as well as a stratigraphic framework has been established. Besides, the diagenetic processes of Changxing Formation consist of compaction, pressure-solution, cementation, dolomitization and dissolution. A comprehensive analysis of lithology, thin section, core description and geochemical data reveals that cementation is the major cause of porosity-loss for primary and secondary pores. Contrary to the adverse impact of cementation on reservoir space, polygenetic dolomitization and dissolution greatly improve the carbonate rocks reservoir and permeability. Structure-controlled hydrothermal dolomitization and burial dissolution play key roles in pore reconstruction. Sequence stratigraphic framework constrains the distribution of diagenesis, which result that dolomitization is most evident in reef cap of highstand system tract (HST), and locally occur in reef base of transgressive system tract (TST) and below maximum flooding surfaces (MFS). The dolomitic reservoirs in HST of Sq2 and TST of Sq1 show high porosity and display a banding distribution along the platform margin. The study indicates that within the sequence stratigraphic framework, dolomitization becomes a guideline of effective reef reservoirs distribution.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016