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Coupling Petrophysics and Petroleum Systems Modeling: A Shale Oil Application from Saudi Arabia


Recent petroleum systems simulator technology improvements allow for bigger models (about a 100 million cells) and capturing much finer scales (below 20m), which especially enhance the modeling of unconventionals, such as shale oil and gas applications for resource assessment. The role of the petroleum systems modeling is to provide the shale maps for maturity, mechanical properties (porosities, fluid pressures, rock stresses), and oil/gas in place properties and volumes. Most input and calibration data can be derived from petrophysical data, but require new workflows for upscaling and calibration. The petrophysical analysis delivers: (i) the shale layer texture and distribution of the lithological components, (ii) framework and distribution of the porosity types (iii) organo-facies type and distribution (iv) oil and gas saturations in place. These properties have to be upscaled and translated to detailed source rock analysis taking into account many new or refined features for the relevant processes. The organo-facies models consist of multi-component approaches including modeling of bitumen and non-hydrocarbon gases. The compaction models also consider isolated pores and secondary organic porosity. Pore-pressure models include hydrocarbon generation pressure, PVT effects and rock stress models specifically used for an advanced failure and fracture prediction. Models for adsorptions are formulated for multi-components. The role of immobile petroleum and the transport within the source rock and at the source/overburden interface is modeled with a new Darcy flow method accurately taking into account the source rock specific relative permeability and capillary entry pressure curves. All these new approaches require understanding of the relevant input parameters at the pore scale and most of them are provided and derived from petrophysical analysis. A specific workflow is especially developed for the calibration of measured saturations with the coupled adsorption/retention/migration/expulsion models. The application of the above procedure is presented for the Cretaceous Shale in the Rub-Alkalhi Basin in Saudi Arabia. This modeling project was part of the unconventional resource assessment of this basin. The linkage between petroleum systems modeling and petrophysical analyses also improve the modeling of conventional petroleum systems.