Electromagnetic wave logging system for determining resistivity and dielectric constant of earth formations

• US 4,107,598 A
• Filed: 05/25/1977
• Issued: 08/15/1978
• Est. Priority Date: 02/02/1976
• Status: Expired due to Term

• Current Assignee: Texaco Incorporated (Chevron Corp.)
• Original Assignee: Texaco Incorporated (Chevron Corp.)
• Inventors: Thompson, Larry W., Meador, Richard A., Fuchs, James A., Cox, Percy T., Adams, Larry L.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US05/800,500
• Time in Patent Office: 447 Days
• Field of Search: 324/6, 324/85
• US Class Current: 324/341
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00
• CPC Class Codes: G01V 3/28 using induction coils

Abstract

A system operating at radio frequencies in the range of 10 MHZ to 60 MHZ is provided for simultaneously determining the resistivity and dielectric constant of earth formations in the vicinity of a well bore. A transmitter coil and two longitudinally spaced receiver coils are provided in the system. Circuit means for measuring the unnormalized amplitude ratio and the relative phase shift of electromagnetic waves at the spaced receiver coils are provided. A relationship is given whereby the formation dielectric constant and resistivity may be obtained from the amplitude ratio and relative phase shift measurements.

Claims

1. A method for determining the electromagnetic properties of earth formations in the vicinity of a well borehole, comprising the steps of:

generating propagating electromagnetic waves at a frequency of approximately 30 megahertz in a well borehole;

detecting said propagating electromagnetic waves at a first shorter longitudinally spaced location in the borehole and converting said detected waves to a first intermediate frequency signal at least two orders of magnitude less than said generated frequency while preserving absolute phase and amplitude information present on said detected waves in the conversion process;

detecting said propagating electromagnetic waves at a second, longer longitudinally spaced location in the borehole and converting said detected waves to a second, different frequency, intermediate frequency signal at least two orders of magnitude less than said generated frequency while preserving absolute phase and amplitude information present on said detected waves in the conversion process;

transmitting said first and second intermediate frequency signals to the surface of the earth;

receiving, at the surface of the earth, said first and second intermediate frequency signals and extracting therefrom the unnormalized ratio of the amplitude components present at said first and second longitudinally spaced locations in the borehole and the relative phase shift of said propagating waves between said first and second longitudinally spaced locations in the borehole; and

recording said unnormalized amplitude ratio and said relative phase shift as a function of borehole depth.

2. The method of claim 1 and further including the steps of deriving from a predetermined relationship the dielectric constant and resistivity of earth formations in the vicinity of the borehole as a function of said unnormalized amplitude ratio and said relative phase shift information.

3. The method of claim 1 wherein the steps are performed repetitively at different depth levels in the borehole and the relative phase shift and unnormalized amplitude ratio information is recorded as a function of borehole depth.

4. The method of claim 2 wherein the steps are performed repetitively at different depth levels in the borehole and the dielectric constant and resistivity is recorded as a function of borehole depth.