Method and apparatus for detecting subsurface anomalies

• US 4,835,474 A
• Filed: 11/24/1986
• Issued: 05/30/1989
• Est. Priority Date: 11/24/1986
• Status: Expired due to Fees

• Current Assignee: Southwest Research Institute
• Original Assignee: Southwest Research Institute
• Inventors: Owen, Thomas E., Parra, Jorge O., Duff, Bob M.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): EDMONDS, WARREN
• Application Number:
  US06/933,871
• Time in Patent Office: 918 Days
• Field of Search: 324/347, 324/354, 324/357, 324/360, 324/363, 324/364, 324/358
• US Class Current: 324/363
• CPC Class Codes: G01V 3/02 operating with propagation of electric current

Abstract

A method and apparatus for collecting measurements on the surface of the earth in a form which can be processed to obtain enhanced resolution of subsurface resistivity anomalies in the earth'"'"'s geologic structure. The system of the preferred embodiment utilizes many separately acquired voltage and current measurements on the earth'"'"'s surface in a superposition analysis to "synthesize" the condition whereby the many separate measurements are acquired simultaneously to give useful advantages in improved depth of investigation commonly known as focused resistivity measurements.

Claims

1. A system for detecting the existence of subsurface anomalies, comprising:

a plurality of means for coupling electric current into the earth;

a plurality of addressable switching means, each of said switching means being connected to one of said plurality of means for coupling electric current, each of said switching means being responsive to a unique address signal to temporarily electrically activate its associated means for coupling electric current;

means for providing a series of address signals to said switching means to sequentially activate each of said switching means to cause each said means for coupling current to inject a quantity of current into the earth in a predetermined sequence;

means for measuring the resultant electric potential gradients produced by each of said means for coupling current and for producing a data set representation thereof;

means for processing the data sets corresponding to each of said means for coupling current to obtain a synthetically-derived resistivity representation of an equivalent potential gradient produced by said plurality of means for coupling current being simultaneously energized; and

means for correlating said synthetically-derived resistivity equivalent representation of said gradient with the location of a geologic anomaly.

2. A system according to claim 1, said means for coupling electric current comprising a plurality of electrodes in a spaced linear pattern.

3. A system according to claim 1, said means for coupling electric current comprising a plurality of electrodes in a spaced two dimensional array.

4. A method for detecting subsurface geologic anomalies, comprising the steps of:

placing first, second, and third electrodes at the surface of the ground to be tested for the existence of anomalies;

sequentially providing said first, second, and third electrodes with a quantity of electric current, said current creating a potential gradient in the ground near said electrodes;

measuring the potential gradient at the surface in the vicinity of the each of said electrodes during the time each said electrode is provided with electric current, thereby obtaining first, second, third data sets corresponding to the potential gradients produced by said electrodes; and

processing said first, second, and third data sets to obtain a synthetically-derived resistivity equivalent representation of the potential gradient produced by three electrodes simultaneously provided with said quantity of electric current; and

correlating said synthetically-derived resistivity equivalent representation of potential with the location of an anomaly in said ground.

5. The method according to claim 4, said first, second and third electrodes being in a spaced linear pattern.

6. A method for detecting subsurface geologic anomalies, comprising the steps of:

placing a set of electrodes at a first position at the surface of the ground to be tested for the existence of anomalies, said electrodes being in a spaced linear pattern;

sequentially providing each of said electrodes in said set with a quantity of electric current, said current creating a potential gradient in the ground near each of said electrodes;

measuring the potential gradient at the surface in the vicinity of the each of said electrodes during the time each said electrode is provided with electric current, thereby obtaining data sets corresponding to the potential gradients produced by each of said electrodes;

moving said set of electrodes to a second position at the surface of the ground to be tested, said electrodes being in a spaced linear pattern parallel to said first spaced pattern;

sequentially providing each of said electrodes in said set with a quantity of electric current, said current creating a potential gradient in the ground near each of said electrodes;

repeating said steps of moving said set of electrodes, sequentially activating said electrodes and measuring said potentials until the ground to be tested has been completely surveyed; and

processing said data sets obtained at each position to produce a synthetically-derived resistivity equivalent representation of the potential gradient produced by a two dimensional array of electrodes simultaneously provided with said quantity of electric current; and

correlating said synthetically-derived resistivity equivalent representation of potential with the location of an anomaly in said ground.