A geological based reservoir zonation scheme in a sequence stratigraphic framework: A case study from the Permo–Triassic gas reservoirs, Offshore Iran

Abstract

Reservoir zonation can lead to an insight about the lateral and vertical distribution of reservoir and non–reservoir zones from bore hole to regional scales. Based on available data sets, scale of study and purposes, there are various reservoir zonation schemes, but correlatability is crucial in any reservoir zonation procedure. In this study, it is attempted to create a reservoir zonation scheme based on geological attributes in the Permo–Triassic successions of the eastern Persian Gulf area, which can be used to inter–field (regional) investigation and correlation. Then, the applicability of two routinely used reservoir zonation procedures including hydraulic flow units (HFU) and flow units based on a stratigraphic modified Lorenz plot was examined. The petrophysical based HFUs were not correlatable between the studied wells and fields. The larger scale flow units were correlatable at the field and to some extent inter–field scales. But, the identified geological reservoir zones (GRZs) were correlatable at both intra– and inter–field scales in a sequence stratigraphic framework. GRZs were defined based on sharp changes in depositional facies, diagenetic features or both and also any meaningful accompaniment in diagenetic features and pore types, which show similar sequence stratigraphic positions. This indicates a close relationship between the depositional sequences and post–depositional diagenetic processes, and therefore GRZs are linked to a sequence stratigraphic framework. The GRZ concept may be applicable to reservoir characterization of the Permo-Triassic successions in the Persian Gulf and adjacent areas. However, this concept can only be applied if the combined depo-diagenetic processes and the resulting reservoir quality are controlled by sequence stratigraphic position without pervasive and non-facies related late diagenetic overprints.