A Differential Resistivity Logging Method for Through-casing Formation

Abstract

The invention discloses a casing-pipe-penetrating stratum differential resistivity logging method. The method includes the steps that a transmitting coil is excited in a cased well in a transient stimulation mode to generate continuous electromagnetic induction transient signals so as to generate eddies in a stratum; a receiving coil receives an electromagnetic induction response waveform; electromagnetic induction response waveforms measured at the adjacent depth positions are subjected to subtraction, direct coupling signals of a casing pipe and the stratum and eddy electromagnetic inductionsignals of the casing pipe are removed, and only the difference between eddy electromagnetic induction signals of two adjacent points of the stratum remains; a scale system is used for conducting scaling on the measured signal difference to obtain the conductivity difference of the stratum; an integral method is used for converting the conductivity difference of the stratum into the conductivityof the stratum; and the reciprocal of the conductivity of the stratum is obtained so as to obtain a resistivity value of the stratum, and a continuous stratum resistivity curve can be obtained after continuous measurement at all depth positions. By measuring the electromagnetic induction response waveforms in the cased well, an eddy field of the cased well is eliminated, and non-contact continuousmeasurement of the casing-pipe-penetrating stratum resistivity is achieved.

Description

technical field [0001] The invention belongs to the technical field of special instruments for measuring physical parameters of casing well formations and evaluating lithology in petroleum engineering well logging construction, and more specifically relates to a differential resistivity logging method for through-casing formations. Background technique [0002] In the process of petroleum development, it is very important to measure the formation resistivity of the cased well and obtain the formation resistivity data under the condition of the cased well. Because the resistivity of the formation directly shows the change of the oil content of the formation, it can be used to analyze the water flooding situation of the oil layer during the development process, and provide a scientific basis for adjusting the development plan. However, the presence of casing in a cased well adds a lot of trouble to the measurement of formation resistivity. Because the casing has a great influ...

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Problems solved by technology

However, the existence of the casing in the cased hole adds a lot of trouble to the measurement of formation resistivity

Because the casing has a great influence on the electromagnetic signal, the electrical conductivity and magnetic permeability of the casing are very high, and electromagnetic waves and high-frequency electromagnetic induction signals cannot pass through the casing and enter the formation. Usually, people use the direct current method to measure the resistance of the formation. rate, push the electrode against the inner wall of the casing, and supply power to the casing and the formation through the electrode. After the current is stable, measure the current and voltage flowing through the formation to obtain the resistivity of the formation. This method can only be measured at fixed points, and the current needs to be stabilized before It takes a certain amount of time to measure each point, so the logging time is low

The current mainly flows along the casing, the current entering the formation is very small, the effective signal amplitude of the measurement is very small, the measurement sensitivity is low, and the contact degree between the electrode and the casing has a great influence on the measurement result

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