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Calibration of NMR Permeability Using Cluster Analysis and Cloud Matching


Petrophysical characterization of heterogeneous carbonate reservoirs has always been difficult (Akbar 1995). Carbonate rocks can have a variety of pore geometries due to the complexity of their deposition which is further complicated by diagenesis.

Understanding the pore structure is crucial to the determination of permeability and the evaluation of a reservoir’s flow behavior. While the NMR tool has helped engineers and geologists evaluate the pore size distribution in carbonates, quantitative determination of permeability has remained a challenge. Multiple laboratories and authors (Arns 2007, Wampler 2010, Chen and others 2017) have attempted to calibrate NMR-derived permeability with core data, but such attempts are tedious and require additional inputs and specialized equipment like core computed tomography (CT), capillary pressure and NMR testing of plugs.

This paper presents a novel technique of calibrating log NMR data to routine core analysis permeability. Using cluster analysis on hydraulic units from a unified core dataset, regional porosity-permeability correlations are created which are used to develop NMR transforms by cloud matching. The workflow is then used to estimate permeability and hydraulic units for uncalibrated wells in the area. This simple technique requires no additional data or testing and can be optimized using a spreadsheet or code. This paper presents the methodology as demonstrated for the San Andres Formation, a complex carbonate in the Permian Basin.