SYSTEM AND METHOD FOR DETECTING A FRACTURE IN A ROCK FORMATION USING AN ELECTROMAGNETIC SOURCE

• US 20140239956A1
• Filed: 02/28/2013
• Published: 08/28/2014
• Est. Priority Date: 02/28/2013
• Status: Active Grant

• Current Assignee: Chevron USA Incorporated (Chevron Corp.)
• Original Assignee: Chevron USA Incorporated (Chevron Corp.)
• Inventors: Alumbaugh, David Lee, Hoversten, Gary Michael
• Granted Patent: US 9,377,552 B2
• Time in Patent Office: Days
• US Class Current: 324/334
• CPC Class Codes: G01V 3/083 Controlled source electromagnetic [CSEM] surveying
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005
• CPC Class Codes: G01V 3/38 Processing data, e.g. for analysis, for interpretation, for correction

Abstract

A surface electromagnetic survey system and method for detecting a fracture or fracture zone in a rock formation are provided. The system includes an electromagnetic source configured to generate an electromagnetic field in the vicinity of or at a surface of the rock formation. The electromagnetic source includes one or more electric dipole sources that are arranged so as to generate a substantially vertical electric field. The system also includes an electromagnetic receiver associated with the electromagnetic source, the electromagnetic receiver being configured to measure a component of the electromagnetic field at the surface of the rock formation; and a processor configured to convert the measured component of the electromagnetic field measured at the electromagnetic receiver into an electromagnetic field response per unit moment of the electromagnetic source. The electromagnetic field response provides information about characteristics parameters of the fracture or fracture zone.

Claims

1. A surface electromagnetic (EM) survey system for detecting a fracture or fracture zone in a rock formation, the system comprising:

an electromagnetic source configured to generate an electromagnetic field in a vicinity or at a surface of the rock formation, wherein the electromagnetic source includes one or more electric dipole sources that are arranged in the vicinity of the surface or at the surface so as to generate a substantially vertical electric field;

an electromagnetic receiver associated with the electromagnetic source, the electromagnetic receiver being configured to measure a component of the electromagnetic field at the surface of the rock formation; and

a processor configured to convert the measured component of the electromagnetic field measured at the electromagnetic receiver into an electromagnetic field response per unit moment of the electromagnetic source, wherein the electromagnetic field response provides information about characteristics parameters of the fracture or fracture zone.

2. The system according to claim 1, wherein the one or more electric dipole sources are disposed vertically at a shallow depth from the surface within the rock formation.

3. The system according to claim 1, wherein the electromagnetic source includes a plurality of electric dipole sources disposed horizontally and oriented radially about a center point so as to produce the substantially vertical electric field beneath the center point.

4. The system according to claim 1, wherein the characteristics parameters of the fracture or fracture zone include an orientation of the fracture or fracture zone, a location of the fracture or fracture zone, a dimension of the fracture or fracture zone, or an extent of the fracture or fracture zone, or any combination thereof.

5. The system according to claim 1, wherein the electromagnetic receiver includes one or more electric or magnetic field receivers that are configured to measure in a time domain or in a frequency domain.

6. The system according to claim 1, wherein the electromagnetic receiver is configured to measure the component of the electromagnetic field before fracturing the rock formation to obtain a first electromagnetic response, and to measure the component of the electromagnetic field after fracturing the rock formation to obtain a second electromagnetic response.

7. The system according to claim 6, wherein fracturing the rock formation includes injecting a conductive fluid into the rock formation to increase an electrical conductivity of the rock formation by displacing less conductive fluids that naturally exist within the rock formation.

8. The system according to claim 6, wherein the processor is configured to compute a percent change from the first and second electromagnetic responses.

9. The system according to claim 8, wherein the electromagnetic source and the electromagnetic receiver are disposed within a line along which the electromagnetic source and the electromagnetic receiver are moved, wherein the component of the electromagnetic field received by the electromagnetic receiver is along the line.

10. The system according to claim 8, wherein the electromagnetic source and the electromagnetic receiver are disposed in a line that is substantially perpendicular to a line along which the electromagnetic source and the electromagnetic receiver are moved.

11. The system according to claim 1, wherein the electromagnetic field response provides information about fracture zone geometry including orientation, extent, or density, or any combination thereof.

12. A method for detecting a fracture or fracture zone in a rock formation using a surface electromagnetic (EM) survey system, the method comprising:

generating, using an electromagnetic source, an electromagnetic field in a vicinity or at a surface of the rock formation, the electromagnetic source includes one or more electric dipole sources that are arranged in the vicinity of the surface or at the surface so as to generate a substantially vertical electric field;

measuring, using an electromagnetic receiver associated with the electromagnetic source, a component of the electromagnetic field at the surface of the rock formation; and

converting, using a processor, the measured component of the electromagnetic field measured at the electromagnetic receiver into an electromagnetic field response per unit moment of the electromagnetic source, wherein the electromagnetic field response provides information about characteristics parameters of the fracture.

13. The method according to claim 12, wherein generating the electromagnetic field using an electromagnetic source comprises generating the substantially vertical electric field using one or more electric dipole sources that are disposed vertically at a shallow depth from the surface within the rock formation.

14. The method according to claim 12, wherein generating the electromagnetic field using an electromagnetic source comprises generating the substantially vertical electric field using a plurality of electric dipole sources disposed horizontally and oriented radially about a center point so as to produce the substantially vertical electric field beneath the center point.

15. The method according to claim 12, wherein the characteristics parameters of the fracture or fracture zone include an orientation of the fracture or fracture zone, a location of the fracture or fracture zone, a dimension of the fracture or fracture zone, or an extent of the fracture or fracture zone, or any combination thereof.

16. The method according to claim 12, wherein the measuring comprises measuring, by the electromagnetic receiver, the component of the electromagnetic field before fracturing the rock formation to obtain a first electromagnetic response, and measuring the component of the electromagnetic field after fracturing the rock formation to obtain a second electromagnetic response.

17. The method according to claim 16, further comprising fracturing the rock formation by injecting a conductive fluid into the rock formation to increase an electrical conductivity of the rock formation by displacing less conductive fluids that naturally exist in pores, cracks and fractures within the rock formation.

18. The method according to claim 16, further comprising computing, by the processor, a percent change from the first and second electromagnetic responses.

19. The method according to claim 18, disposing the electromagnetic source and the electromagnetic receiver within a line along which the electromagnetic source and the electromagnetic receiver are moved, the component of the electromagnetic field received by the electromagnetic receiver is along the line.

20. The method according to claim 18, further comprising disposing the electromagnetic source and the electromagnetic receiver in a line substantially perpendicular to a line along which the electromagnetic source and the electromagnetic receiver are moved.

21. The method according to claim 12, further comprising providing information about fracture zone geometry including orientation, extent, or density, or any combination thereof.