Abstract:

Nuclear magnetic resonance logging has an edge on the evaluation of porosity structures over the traditional mercury-injection capillary pressure method.For oil reservoirs with low-porosity and low-permeability,the variations in pore structures have a significant impact upon the saturation index 'n',i.e.,when big pores dominate,the 'n' is small;and when small pores dominate,the 'n' is big.The good correlativity between 'T₂',the geometric mean of lateral relaxation time of nuclear magnetic resonance,'m',the cementation index,and 'n',the saturation index,can be used to determine the values of 'm' and 'n'.The errors of value assignment caused by changes of pore structures are eliminated,thus a more accurate value for 'S₀.'(oil saturation) can be obtained from saturation model.The processing of the data in Well TZ111 yields a porosity free of influence of pore enlargement and a saturation closer to the testing results,greatly improving the accuracy of the saturation model.

Key words: geometric mean of T₂, cementation index, saturation index, pore structure, nuclear magnetic resonance, oil saturation