Spatial Modeling of Jurassic Arab Formation Hierarchical Carbonate Depositional Environment Tracts as a Guide to Reservoir Connectivity Anisotropies: An Example from the Dukhan Field, State of Qatar

The Arab C reservoir interval of Qatar Petroleum’s Dukhan Field is a prolific oil producer. After sixty years of development activity and with hundreds of logged and cored wells, there is an extensive database of rock, geophysical and production surveillance information available for interrogation. The reservoir hosts an accumulation of carbonate lithologies and textures representing a depositional organization of subtidal, intertidal and sabkha environments. A Transgressive System Tract defines the Lower Arab C, migrating upwards from a complex of beach grainstones to a maximum flooding surface featuring muddy carbonates with sporadic encrustations and associated Thrombolite growths. High frequency parasequences within the overlying Highstand System Tract (HST) of the Upper Arab C form a sedimentological pattern from intertidal to sabkha facies, with increasing prevalence of thin isolated high productivity grainstones. From a practical engineering perspective, the upper parts of the HST collocate with development uncertainties associated with erratic patterns of producer support from offset water injectors. Core descriptions characterize these intervals as low permeability mud dominated tidal flats hosting sporadic conductive grainstone tidal channels, leeward of beach barrier islands. Qatar Petroleum has adopted coastal hydrodynamic principles to predict grainstone anisotropic variations. The model for the shelf area has been compartmentalized into depositional tracts based on core descriptions, supplemented by predicted facies at non-cored vertical and horizontal wells using inter-dependent 3D-spatial and 1D log-based fuzzy probability. Vector representations of interpreted tidal flux directions have been used to assign analogy-realistic geometries for beach and tidal channel deposits within an environment of deposition framework. The output distributions reflect a close coupling of control data at wells within the context of sedimentary depositional dynamics, linked to production surveillance. An objective for high resolution 3D static modeling of rock textural and petrophysical anisotropy is the optimization of future infill horizontal wells to maximize IOR sweep efficiency.