Borehole time domain pulse electromagnetic method for detecting electrical resistivity of stratum out of metal bushing

Abstract

The invention discloses a borehole time domain pulse electromagnetic method for detecting the electrical resistivity of the stratum out of a metal bushing, comprising the following steps of: 1) building a large-power pulse emitting source underground; receiving the time variable data of induced electromotive force e produced by a magnetic field vertical component Bz recorded in the recording system; and simultaneously recording emitting wave type and receiving signal; 2) emitting and receiving several times, and overlapping signals to improve the signal to noise ratio; 3) calculating bushing response according to the bushing parameter and the recorded emitting source current wave type to obtain the induced electromotive force delta epsilon f relative to the stratum out of metal bushing; 4) correcting the relative induced electromotive force; 5) one-dimensionally reversing and transforming the time variable observed signal into the radial variation information of the electrical resistivity of the stratum around the well; 6) obtaining the longitudinal and radial two-dimensional images of the electrical resistivity of the stratum out of the borehole bushing through the reversed electrical resistivity; 7) confirming the distributing situation of the surplus oil in the storage layer through the distribution of the electrical resistivity of the storage layer out of the bushing according to the survey data and the explained result when well completion.

Description

technical field [0001] The invention relates to the technical field of well geophysical measurement and oilfield development, in particular to a method for obtaining the distribution information of the formation resistivity around the wellbore outside the casing by exciting and observing the change of the electromagnetic field in the casing well, and then evaluating the development of the oil reservoir. In-well electromagnetic detection method of remaining oil distribution state. Background technique [0002] Since the electrical parameters of the reservoir medium are closely related to the reservoir porosity, pore fluid properties, and saturation, the electrical properties of the reservoir when it contains oil and gas are very different from those when it contains formation water, and the electrical parameters of the reservoir medium It is a main parameter for judging and evaluating the hydrocarbon-bearing properties of reservoirs, so the electrical or electromagnetic metho...

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Problems solved by technology

This kind of cleaning work is expensive, and if the cleaning is not thorough, it will lead to poor contact and large measurement errors. This problem is caused by the limitations of the observation method.

Measurements in direct contact with the pipe wall are more susceptible to casing collars and perforation points, making data interpretation difficult

Furthermore, this method uses DC current power supply to diffuse into the formation through the casing, and the DC diffusion field itself has no sounding ability, and can only identify the resistivity of formations at different depths by changing the electrode distance; due to the limitation of logging cables, The power supply current cannot be very large (<6A), so the detection depth of this method is very limited

In this way, the cement sheath has an important impact on the observation data, and needs to be finely processed and corrected in the interpretation, and the resistivity distribution information of the reservoir within a certain distance from the wellbore wall is even more difficult to obtain.

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