Kashagan is a world-class supergiant oil field located in Kazakhstan, in the offshore of Caspian Sea. The reservoir is an isolated carbonate platform, Devonian to Carboniferous in age.
Definition of petrophysically significant Reservoir Rock Types (RRT) is critical in the reservoir characterisation and the dual petrophysical-geological significance of these RRTs is fundamental in providing a link to geological model drivers.
Kashagan carbonate field core studies highlight no relationship between lithofacies and petrophysical characteristics because of the strong diagenetic overprint. A RRT classification has been therefore performed integrating petrophysical data, Phi-K-MICP, with sedimentological, diagenetical and petrographical data. This process has allowed the definition of 7 RRTs that have been propagated into the Log domain using the kNN algorithm.
The resulting Log RRTs have been analysed in term of spatial distribution and petrophysical meaning. Their main geological driver is the 4th order cyclicity with a link to the Environment of Deposition, Karst intervals and Diagenetic Reservoir Quality Maps. The 3D modelling of RRTs should be therefore driven by VPC per 4°order cycles, obtained for each 3° order System Tract, consistently with both EoD and RQ Maps.
Core plugs and whole cores, "labelled" according to Log RRT propagation, have been analysed and characterised in terms of both K vs. Phi and Sw vs. Height relationships. Whole cores RRT show, systematically, higher K vs. Phi trends. This fact has been interpreted as a scale factor. Whole core K/Phi relationships have been therefore utilized for the synthetic permeability estimation. The KH-RRTs vs. KH-Well-Test comparison shows a good agreement in Platform Interior where wells are mainly producing from matrix, while in the Rim a large gap, due to Fractures and Megakarst, has been recognized.