Reservoir characterization of the Burgan Formation in northwestern Persian Gulf

Abstract

Lower Cretaceous sequences of the Burgan Formation are notable siliciclastic reservoirs in the Middle East. Despite of this importance, a little is known about various geological characteristics of this reservoir in Iranian northwestern part of the Persian Gulf. In this study, an integrated sedimentological and reservoir geological evaluation has been carried out on the Burgan reservoir using a complete dataset of drilled cores, core plugs, thin sections and petrophysical logs along with laboratory data including XRD analysis of all components to define grain's mineralogy and porosity – permeability data for reservoir quality evaluation. Depositional facies and environments are interpreted and correlated in sequence stratigraphic framework of targeted reservoir across the studied fields and then compared with stratigraphic equivalents in the Middle East. Seven facies types are recognized that indicate deposition in a transitional environment from siliciclastic-dominated delta setting into shallow-marine carbonate platform. Diagenesis study indicates a simple history of post-depositional events that includes near surface (marine) and shallow to deep burial realms. Diagenetic processes are grouped into two categories based on their effects on reservoir properties. They include porosity enhancing (i.e. dissolution and fracturing) and porosity reducing (compaction and cementation) diagenetic processes. Reservoir evaluation of depositional facies has been carried out by defining petrographic rock-types (PRTs) and hydraulic flow units (HFUs) and their correlation in sequence stratigraphic framework. Results showed that semi-to unconsolidated sandstone facies accumulated in Burgan-B member provides the best reservoir units in the Burgan Formation. Organic-rich (rootled) and pelagic shale facies form several intra-reservoir barriers between the reservoir units, especially in Burgan-A member. These show close correlation with reservoir descriptions of this formation reported from the neighboring areas in the Persian Gulf (i.e. Kuwait).