Comparison Between Stoneley, Nmr, And Core-Derived Permeabilities

Formation permeability is the key to reservoir characterization and management. Wireline acoustic and nuclear magnetic resonance (NMR) logging can now provide continuous permeability index profiles. With the proper calibration of formation fluid parameters for the acoustically obtained permeability index and petrophysical model parameters for the NMR obtained permeability index, we can now map the permeability index to laboratory derived permeabilities. In the Smørbukk field, Mid Norway, the reservoir is located at a depth from 3500 m to 5000 m. The reservoir quality is controlled by sedimentary facies variation, quartz cementation and primary sand quality, secondary porosity, and the presence of illite and grain coating chlorite. This makes the reservoir very heterogeneous, resulting in strong permeability changes on a vertical scale much smaller than the vertical resolution of NMR and Stoneley derived permeability. In this paper we will analyse three wells of the Smorbukk field and demonstrate that after applying proper vertical avenging to the core data, we obtain a good match between Stoneley, NMR and core permeability. However, one stratigraphic unit appears in all three wells, which was cored in two of these wells. This unit shows a consistent mismatch between core and NMR/Stoneley derived permeabilities. This mismatch will be explained by a "borehole damage" theory.