A well logging system for determining the water resistivity and the water saturation in an earth formation traversed by a borehole, a well logging sonde including:
- first transmitter means for transmitting electromagnetic energy at a first frequency, lying within the range of frequencies from 10 MHz to 200 MHz into the earth formation,
- second transmitter means for transmitting electromagnetic energy at a second frequency, lying within the range of frequencies from 10 MHz to 200 MHz into the earth formation,
- a first pair of receiver means spatially related to the first transmitter means for receiving electromagnetic energy from the earth formation and providing signals representative thereof,
- a second pair of receiver means spaced a predetermined distance apart and spatially related to the second transmitter means for providing signals representative of electromagnetic energy received from the earth formation,
- first signal means for providing signals relating to the electromagnetic energy transmitted by the first transmitter means and received by the first pair of receiver means,
- first parameter means connected to the first signal means for providing signals corresponding to the phase difference between the signals provided by the pair of receiver means and for providing a first ratio signal corresponding to the ratio of the amplitudes of the signals provided by the first pair of receiver means,
- second signal means connected to the second pair of receiver means for providing signals representative of the electromagnetic energies received by the second pair of receiving means,
- second parameter signal means connected to the second signal means for providing a second phase difference signal corresponding to the phase difference between the signals provided by the second signal means and providing a ratio signal corresponding to the ratio of the amplitudes of the signals provided by the second signal means,
- first means connected to the first parameter signal means for deriving a dielectric constant and a resistivity in accordance with the phase difference signal and a the ratio signal from the first parameter signal means,
- second means connected to the second parameter signal means for deriving a dielectric constant and a resistivity in accordance with the phase difference signal and the ratio signal from the second parameter signal means;
- means for transmitting the dielectric constant signals and the resistivity signals to the surface;
- and
- surface signal processing means including:
- means for providing a signal corresponding to porosity, and
- means connected to the porosity signal means and to the transmission means for deriving the water saturation and the resistivity of the water in the earth formation in accordance with both phase difference signals and both dielectric constant signals and the porosity signal.