Effect of Pore Size Distribution on Fluid Movement in Complex Reservoirs

Abstract In the pursuit of maximizing hydrocarbon recovery, accurate reservoir characterization is crucial for effective oil and gas field development. A key challenge lies in understanding the reservoir performance and maintaining optimal reservoir pressure to enhance flowing efficiency and increase recoverable reserves. However, carbonate formations pose significant complexities due to their texturally varied and heterogeneously porous structures, as well as variable salinity. To address these challenges, this analysis undertakes a comprehensive evaluation to estimate fluid saturations within complex reservoir. Dielectric dispersion measurements, Nuclear Magnetic Resonance (NMR), and new generation downhole formation tester are combined for operational insight and reservoir description. Fluids saturation from deep resistivity and porosity is optimized using dielectric log and reconstruction from multi-physics inversion to guide textural parameters selection; accurate downhole water resistivity measurements were utilized in this analysis. Shallow NMR bound fluid volume and dielectric water-filled porosity correlation and comparison with total porosity discriminates between movable and immovable fluids. NMR porosity spectral analysis then describes variable facies explaining the changes in oil fractions and ability to flow. Heterogeneous rock quality and fluids distribution on an heterogeneous reservoir was successfully evaluated. Porosity and fluids volumes were accurately quantified; a novel multi-physics inversion workflow provides important quality control and validation to unlock the complexity of the pore structure system utilizing petrophysical logs. Saturations and flow behaviour are controlled by the pore network and grain sorting developed in the carbonate rock. Different rock facies alternate with zones with larger displacement efficiency and layers with predominance of micropores trapping more immovable oil. Real-time use of dielectric dispersion and NMR logs predicts movable fluid fractions and rock quality controlling the production performance without the need for more extensive methodologies. Comprehensive downhole sampling program optimized using petrophysics logs confirms the movable fluid fractions and their properties. The ability to deliver representative in-situ water resistivity is beneficial to real-time dielectric logs processing and deep saturation assessment for more confident evaluation of the near wellbore and properties variations radially into the formation. Better consideration of changes in rock quality and production potential is achieved, adding important knowledge to the overall understanding of the complex reservoir behaviour. A multi-physics multi-domain workflow is applied to accurately describe the main rock parameters that control complex fluid movability in heterogeneous carbonate facies. A new downhole calibrated resistivity measurement was utilized to confirm vertical salinity variation.