Methods for magnetic imaging of geological structures

Abstract

Methods for imaging geological structures include injecting magnetic materials into the geological structures, placing at least one magnetic probe in a proximity to the geological structures, generating a magnetic field in the geological structures and detecting a magnetic signal. The at least one magnetic probe may be on the surface of the geological structures or reside within the geological structures. The methods also include injecting magnetic materials into the geological structures, placing at least one magnetic detector in the geological structures and measuring a resonant frequency in the at least one magnetic detector. Methods for using magnetic materials in dipole-dipole, dipole-loop and loop-loop transmitter-receiver configurations for geological structure electromagnetic imaging techniques are also disclosed.

1 . A method for imaging a geological structure, the method comprising:
 providing a dispersion of magnetic material in a fluid, wherein the magnetic material comprises magnetic nanoparticles;   injecting a fluid into the geological structure;   placing at least one magnetic probe in a proximity to the geological structure;   generating a magnetic field with the at least one magnetic probe; and   detecting a post-injection magnetic signal.   
     
     
         2 . The method of  claim 1 , wherein the magnetic probe provides an antenna utilizing a dipole-dipole, dipole-loop, or loop-loop configuration. 
     
     
         3 . The method of  claim 1 , wherein the magnetic probe is an electromagnetic probe that generates an electromagnetic field. 
     
     
         4 . The method of  claim 3 , further comprising detecting an electromagnetic signal, wherein the electromagnetic signal detected is utilized to image the geological structure. 
     
     
         5 . The method of  claim 3 , further comprising detecting an electromagnetic signal velocity. 
     
     
         6 . The method of  claim 1 , wherein the post-injection magnetic signal detected is utilized to image fractures in the geological structure. 
     
     
         7 . The method of  claim 1 , further comprising detecting a prior magnetic signal, wherein the prior magnetic signal is detected before injecting the dispersion of magnetic material into the geological structure. 
     
     
         8 . The method of  claim 7 , wherein the prior magnetic signal is compared to the post-injection magnetic signal to analyze the geological structure. 
     
     
         9 . The method of  claim 1 , wherein the magnetic field is a DC field, an AC field, a pulsed field, or a field that varies in both time and amplitude. 
     
     
         10 . The method of  claim 1 , wherein the magnetic field generated by the magnetic probe is modulated to enable frequency-domain, time-domain, or phase-shift detection. 
     
     
         11 . The method of  claim 1 , wherein the detecting step comprises measuring a resonant frequency. 
     
     
         12 . The method of  claim 1 , wherein the dispersion of magnetic material in the fluid provides a permeability of 50μ o  or greater. 
     
     
         13 . The method of  claim 1 , wherein the dispersion of magnetic material comprises a ferrofluid. 
     
     
         14 . The method of  claim 1 , wherein the magnetic material is selected from the group consisting of iron, cobalt, iron (III) oxide, magnetite, hematite, ferrites, and combinations thereof. 
     
     
         15 . The method of  claim 14 , wherein the ferrites comprise a material having a formula AM 2 O 4 ; wherein A and M are metal atoms; and wherein at least one of A and M are Fe. 
     
     
         16 . The method of  claim 15 , wherein the ferrites are doped with at least one element that is not A or M. 
     
     
         17 . The method of  claim 1 , wherein the magnetic material has a diameter of between 10 nm to 1μm. 
     
     
         18 . The method of  claim 1 , wherein the magnetic material is covered with a coating selected from the group consisting of surfactants, polymers, or combinations thereof. 
     
     
         19 . The method of  claim 1 , wherein the fluid is selected from the group consisting of water, brine, drilling mud, fracturing fluid, and combinations thereof. 
     
     
         20 . The method of  claim 1 , wherein the detecting step is conducted with at least one SQUID detector.