| 摘要 |
A method and apparatus is disclosed for determining the properties of formations surrounding an earth borehole that have been invaded by borehole fluid to form an invaded zone. Properties determined in one embodiment are invaded zone resistivity (Rxo), diameter of invasion (DI), and uninvaded formation resistivity (Rt), and the following steps are performed: (a) suspending a logging device in the borehole; (b) transmitting electromagnetic energy from a transmitter location on the logging device, and receiving the transmitted electromagnetic energy at receiver locations on the logging device for a first transmitter-to-receivers receivers spacing associated with the transmitter and receiver locations; (c) determining, from the received electromagnetic energy, measurement characteristics associated with the first transmitter-to-receivers spacing; (d) repeating steps (b) and (c) for a plurality of further transmitter-to-receivers spacings to obtain measurement characteristics for the plurality of further transmitter-to-receiver spacing; (e) generating a model of formation of resistivity Rt with an invaded zone of resistivity Rxo and diameter of invasion DI; (f) selecting values of Rxo, DI, and Rt that would produce model measurement characteristics that substantially correspond, for each of a plurality of the transmitter-to-receiver spacings, with the actual measurement characteristics for the respective plurality of transmitter-to-receiver spacings; and (g) outputting the selected model values of Rxo, DI and Rt.
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