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| | 講演要旨(英文) | | Porosity is an important parameter for reservoir engineering, environmental geophysics, and hydrogeology. Electrical and electromagnetic methods giving electrical conductivity can be applied to estimate porosity through the relationship between electrical conductivity and porosity. Empirical relationship such as Archie's law relating directly electrical conductivity to porosity is often used to estimate porosity. Electrical conductivity depends theoretically however not only on porosity but also on tortuosity. Computer modelling may help to study behaviour of the tortuosity. We investigated tortuosity defined as the ratio between 'real' flow path and 'sample' length, of three dimensional rock models generated by random number and random sierpinski carpets. Tortuosity obtained from those models ranges from 1.0 - 1.6 for variation of porosity from 20% - 80%.. It is shown that tortuosity increases following power law as porosity decreases with very good correlation. The relationship between tortuosity and porosity are similar independent of fractal dimension of created models. Inserting tortuosity as a function of porosity into the expression of formation factors fits to Archie's law with cementation exponent of about 1.32. This value is close to unconsolidated sands. |
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