Отправлено: 21.05.09 02:52. Заголовок: Permeability prediction for low porosity rocks by mobile NMR

Permeability prediction for low porosity rocks by mobile NMR
H. Papea,d,*, J. Arnolda,c, R. Pechniga,c, C. Clausera,
E. Talnishnikhb, S. Anferovab, B. BlЁ№michb

Abstract
Permeability prediction from NMR well logs or mobile NMR core-scanner data is attractive as the measurements can be performed directly in the formation and on fresh cores right after drilling, respectively. Besides, the method is fast and non-destructive. Compared to T1 relaxation times, commonly measured T2 distributions are influenced by external and internal magnetic field gradients. We performed two-dimensional T1 and T2 relaxation experiments on Rhaetian sandstone samples with low porosity and small pore radii using a mobile NMR core scanner which provides a nearly homogeneous static magnetic field. Because small pore sizes are associated with high internal magnetic field gradients standard methods from NMR logging in the oil industry can not be applied for an accurate permeability prediction. Therefore, a new model theory was developed which describes the pore radius dependence of the surface relaxivity ¦С 2 by both an analytical and a more practical empirical equation. Regarding corrected ¦С 2 values, permeability can be predicted accurately from the logarithmic mean of the T2 distribution from the physically based Kozeny-Carman equation. Additional core plug measurements of structural parameters such as porosity, permeability, specific inner surface area and pore radius distributions provide confidence in the NMR results.

http://www.geophysik.rwth-aachen.de/Downloads/pdf/PapeEtAl_permeabilityPaAGEOPH_2009.pdf