Understanding the role of sequence stratigraphy and diagenesis on the temporal and spatial distribution of carbonate reservoir quality: A conceptual modeling approach

Karst caves formed by meteoric water leaching are important oil/gas storage spaces in carbonate reservoirs. However, carbonate reservoirs are transformed by atmospheric freshwater due to long-term cumulative effects that take place over millions of years, and laboratory physical simulations are therefore difficult to conduct. The mechanism by which meteoric water leaching transforms the carbonate sequence stratigraphy is therefore un-clear, which has hindered the exploration and development of oil/gas resources. In this study, a large set of geological test data was utilized to develop a solute transport numerical simulation model based on multi-phase flow and multi-component reaction. This was then applied to construct a conceptual model of a grade III sequence stratigraphy for a reservoir in the Yingshan Formation in the central Tarim Basin, China. The multi-stage leaching process of meteoric water during the periodic exposure of the sequence stratigraphy was simu-lated to explore the effects of the diagenetic transformation of meteoric water on sequence stratigraphy and the associated physical responses. Results revealed that the composition of carbonate rocks affects the degree of reservoir development under the sequence boundary. Calcite dissolution plays a strong role in meteoric water leaching. Carbonate strata with a high calcite content forms secondary pores relatively easily and dolomite can be preserved. Under open geological conditions, the transformation of reservoirs by meteoric water in different periods has the characteristics of continuity, indirectness, superposition, and heterogeneity. In addition to the mineral dissolution caused by the unsaturated solution of the underlying strata, the transformation was also affected by the superposition and indirect influence of the migration and infiltration of the overlying strata fluid. Under heterogeneous conditions, meteoric water preferentially flowed along the dominant channels, which could improve reservoir performance locally, and may form oil and gas migration channels or large karst caves. This investigation of the control of meteoric water during reservoir development provides a theoretical basis for the genetic mechanism by which a high-quality reservoir can develop under the carbonate sequence boundary.

Automated summary

Karst caves formed by meteoric water leaching play an important role in oil/gas storage in carbonate reservoirs. However, the mechanism by which meteoric water leaching transforms the carbonate sequence stratigraphy is still unclear. In this study, a solute transport numerical simulation model was developed and applied to simulate the effects of diagenetic transformation of meteoric water on sequence stratigraphy. The results provide insights into the factors influencing reservoir development under the carbonate sequence boundary.