Pore-Scale Characterization and Productivity Analysis by Integration of NMR and Openhole Logs: A Verification Study

Presently, NMR logs are routinely used to estimate the irreducible portion of the bulk volume of wetting phase (BVI), permeability and the type of hydrocarbons present when filtrate invasion is limited or non-existent. In most cases, the rest of the pore-scale information contained in NMR log data is overlooked or ignored as the model equations used to infer it are empirical in nature. Our aim in this study is to demonstrate the use of and the degree of accuracy of pore- scale data derived from NMR logs by presenting an actual case study with production test results and comparison to core- based information. This study also demonstrates the importance of NMR based pore-scale characterization if or when the filtrate invasion limits the hydrocarbon typing capabilities. Pore scale characterization is obtained by transforming the NMR data to synthetic capillary pressure and evaluating the dynamic properties of the formation in conjunction with the fluids present. The capillary transformation of NMR data is performed based on experimental models. The BVI from this transformation (RBVI) is tested against the conventional T2cutoff based BVI for accuracy and reliability prior to the determination of Swanson-based Swirr, relative permeability transformations and the critical Swirr that can be used for identifying transition zone. T2cutoff independent BVI (from which Swirr is derived), threshold pressure, mean pore-throat radius, effective permeability to wetting and non-wetting phases and the md-ft evaluation of subject intervals are the end products of this study. The results are compared to production test data to demonstrate the utility of NMR logs both to production/completion engineering and to well/formation economics.