Dielectric constant well logging with current and voltage electrodes

摘要

This invention provides for methods and systems for measuring the dielectric constant of an earth formation. In a preferred embodiment, an alternating current is passed through a portion of the formation and a reference resistor in series with the portion. The capacitance and the dielectric constant of the portion may be determined from the phase difference between the voltage across the reference resistor and the voltage across the portion. This phase difference may be obtained by generating a voltage which is in phase with the voltage across the reference resistor, but which has the magnitude of the voltage across the portion. To obtain the phase difference by an alternate digital method, the voltage across the referenced resistor and the voltage across the portion are each transformed into a square wave signal. The two square wave signals are then compared to obtain the sign and the magnitude of the phase difference between the two square waves. In an alternate preferred embodiment, an alternating current is passed through the portion of the earth formation and through a capacitor and a resistor connected in series with the portion. The first DC signal is generated by filtering out the high frequency components from the product of the voltages across the capacitor and across the portion. A second DC signal is generated by filtering out the high frequency components from the product of the voltages across the referenced resistor and across the portion. The phase difference between the voltage across the portion and the current through the portion may be determined, from which the capacitance and the dielectric constant of the portion may then be calculated.