Pore to Field Scale Rock Typing and Reservoir Characterization

This research was aimed at developing a robust stratigraphic framework, carrying out petrophysical analysis, identifying rock types and fluids within the subsurface formations, and creating robust models for the Gabo Field, Niger Delta Basin. Core images were correlated with an already established facies scheme to build the stratigraphic framework. Using cross plots of formation pressures Vs depth, fluid types, fluid contacts, Free Water Level (FWL), and Height Above Free Water Level (HAFWL) were obtained. Wireline log data were analysed using Python scripts, Hierarchical Cluster Analysis (HCA), and Indexed and Probabilised Self-Organising Map (IPSOM). Rock types were identified using the Flow Zone Index (FZI) approach. A new horizontal line graphical approach to identify rock types was introduced, and the identified rock types were validated with an FZI/Irreducible water saturation (Swi) function. Using contingency tables, the Gabo Field subsurface formations were shown to consist of scale-dependent heterogeneities with depositional environment having varied sedimentary bodies, electrofacies, facies, grain sizes, and hydraulic flow units. To extend the application of the FZI parameter in rock typing, a spherical pore-throat, pore-body model with various functions correlating FZI to end-point saturations of relative permeability data was built. The correlations between Flow Zone Index (FZI)/irreducible water saturation (Swi), FZI/residual oil saturation (Sor), absolute permeability (Ka)/oil permeability at irreducible water saturation (Ko@Swi), Ka/water permeability at residual oil saturation (Kw@Sor), FZI/effective diameter of pore-throat to support water flow (FZIw), and FZI/effective diameter of pore-throat to support oil flow (FZIo) were obtained, and used to describe relative permeability data for a given FZI information in water wet rocks in an oil-water system. Results from this work provided robust models which may also be utilised to investigate deltaic systems in other basins. Also, the knowledge of pore throat diameters might help with future Carbon Capture Utilization and Storage (CCUS) experiments.