Rock-typing In Carbonates: A Critical Review Of Clustering Methods

Abstract

Abstract Carbonate reservoir Rock-Types are generally complex to identify due to the intricate impact of diagenesis on the porous network. Based on a many years of experience working with carbonates, TOTAL has developed over time a dedicated Rock-Typing workflow contingent on the integration of all core and log data at all possible scales (from SEM to field). The result is designated as SRT standing for Static Rock-Types. Considering that the key point of Rock-Typing is to capture as straightforward as possible a relationship between geology and petrophysics, SRT could be considered as a geologically and petrophysically homogeneous group of rocks with specific distributions and relationships between K, Φ and Sw, reflecting the main petrophysical properties. The petrophysical distributions within each Rock-Type must be stationary or homogeneous within petrophysical domain and follow certain geostatistical behaviors. Moreover, there must be a specific and comprehensible link with the geology (lithology, stratigraphy, sedimentology and diagenesis) in order the petrophysics to be extrapolated in 3D. This paper presents a critical review of the most common clustering methods (Lucia, Pittman, RQI, FZI …). Some are geologically driven, others petrophysically driven, some are defined at plug or even core scale, others at log scale. After comparing the pros and cons of each method, the SRT approach reconciles plug to log scale on one side and geology (including diagenesis) and petrophysics on the other side. The discriminating parameters for SRT building have to be found among CCA (Φ, K, ρ), SCAL (Pc, PTR), accurate thin sections description (texture, porosity types, cement types, crystals size), and logs responses (core logs, well logs including imagery and NMR). SRT can consequently be propagated in non-cored intervals through electro-SRT models based on the sedimento-diagenetical model provided by the sedimentologists allowing the 3D distribution of petrophysical properties between the wells.