Nuclear Magnetic Resonance-Driven Integrated Approach for Characterization of Heavy Oil-Bearing Complex Carbonate Reservoirs

Characterizing carbonate rock using petrophysical data can be challenging because of the complex rock properties and variable resistivity responses. This difficulty is exacerbated in the presence of heavy oil, making it hard to evaluate these formations accurately with standard open hole wireline logs alone. To address these challenges, an integrated approach is adopted to address the complexities of heavy oil carbonate reservoirs. The integration of conventional core, Nuclear Magnetic Resonance, image logs, and Elemental Spectroscopy Technologies with conventional logs enabled us to characterize the reservoir properties of the heavy oil carbonate reservoir. Mineral composition and grain density, essential parameters for evaluating carbonate reservoirs, are derived from elemental spectroscopy logs. Image logs play a key role in accurately identify and to characterized fractures and vugs. The heavy oil component "not visible to NMR" is estimated by contrasting NMR total porosity with lithology-corrected density porosity. 2D NMR techniques to map diffusion coefficients (D) against T2​ relaxation times provide improved insights into fluid distribution, contact, and pore characteristics. Conventional core-based XRD quantifies mineral composition, and petrographic slides reveal mineralogical composition & rock microstructure. Together with UV analysis, these methods improve fluid identification. The successful integration of conventional core, NMR, Elemental Spectroscopy Log, along with Image log, enhances the understanding of reservoir properties in the study area. This methodology offers significant advantages over conventional petrophysical techniques, particularly in complex carbonate reservoirs containing high-viscosity oil.