CROSS-REFERENCE TO RELATED APPLICATIONS
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This application is a divisional of U.S. patent application Ser. No. 12/350,914 filed Jan. 8, 2009, which claims priority to provisional patent applications 61/019,765 filed Jan. 8, 2008 and 61/054,362 filed May 19, 2008, which are each incorporated by reference as if written herein in their entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
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Most geological structures relevant to oil and gas production retain between 70% to 90% of their original hydrocarbon stores after primary production driven by natural reservoir pressure release is complete. Hydraulic fracturing is often used to increase reservoir contact and increase production rates. During the fracturing process, proppants are typically added to a fracturing fluid pumped into the geological structure in order to keep the fractures from closing in upon themselves when pressure is released. Another technique commonly used in secondary production is displacement flooding, of which water-flooding is the most common. In flooding techniques, a displacing fluid is introduced from an injection well, and oil and/or gas are extracted from a nearby production well. The displacing fluid frees oil or gas not released during primary production and pushes the oil or gas toward the production well. Displacing fluids include, for example, air, carbon dioxide, foams, surfactants, and water. Hydraulic fracturing is often applied to injection and production wells in conjunction with displacement flooding operations.
In spite of the undisputed utility of hydraulic fracturing and water-flooding in petroleum production processes, few methods exist for monitoring the extent and quality of the fracturing and flooding processes. Fractures can be monitored and approximately mapped three-dimensionally during the fracturing process by a ‘micro-seismic’ technique. The micro-seismic technique detects sonic signatures from rocks cracking during the fracturing process. The setup of this technique is prohibitively expensive, and data that is generated tends to be relatively inaccurate due to high background noise. Further, the process can only be performed during the fracturing process and cannot be repeated thereafter. Water-flood operations can be monitored with low resolution through four-dimensional seismic surveys. As the density difference between water and petroleum is small, the flood front is not abruptly distinguishable, and the imaging resolution tends to be on the order of tens of meters. Unlike the micro-seismic technique for monitoring fracturing, flooding operations can be measured periodically to monitor flooding progression.
Neither of the above techniques have the capability to accurately determine the size, structure and location of injected materials such as, for example, injected proppants and water-flood. Improved knowledge concerning the location of injected proppants and water-flood in fractures and natural geological pores would aid production engineers in tailoring production conditions to meet local geological settings. Further, knowledge about the location of injected proppants and fractures would significantly improve safety in production processes by identifying potentially catastrophic events before their occurrence. For example, vertical fractures can rupture the strata sealing geological structures and potentially intersect fresh water aquifers. Detecting a vertical fracture situation would allow production wells to be sealed, thereby preventing petroleum loss and aquifer damage.
In view of the foregoing, improved methods for imaging geological structures are needed. Such methods would include the capability to obtain high-resolution images of fractures and injected materials, as well as the ability for numerous measurement repetitions to be made. Utilizing such imaging methods solely or in combination with existing geological assays, production engineers could take measures to extract residual petroleum from a geological structure if it is determined that un-extracted hydrocarbons remain after production stimulated by fracturing and flooding operations or a combination thereof is complete.
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In various embodiments, methods for assaying a geological structure are disclosed. The methods include providing a dispersion of magnetic material in a fluid; injecting the dispersion of magnetic material into the geological structure; placing at least one magnetic probe in a proximity to the geological structure; generating a magnetic field in the geological structure with the at least one magnetic probe; and detecting a magnetic signal.
In other various embodiments of methods for assaying a geological structure, the methods include: a) providing a dispersion of magnetic material in a fluid; b) injecting the dispersion of magnetic material into the geological structure; c) placing at least one magnetic detector into the geological structure; and d) measuring a resonant frequency in the at least one magnetic detector. The resonant frequency is at least partially determined by an amount of the magnetic material injected into geological structure and a location of the magnetic material relative to the at least one magnetic detector.
In other various embodiments, methods are disclosed for using magnetic materials in electromagnetic imaging techniques utilizing transmitter-receive antenna configurations such as dipole-dipole, dipole-loop and loop-loop configurations. An illustrative method utilizing such transmitter-receiver antenna configurations includes, for example, travel-time tomography.
The foregoing has outlined rather broadly various features of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter, which form the subject of the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
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For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions to be taken in conjunction with the accompanying drawings describing specific embodiments of the disclosure, wherein:
FIG. 1 presents finite-element modeling of the radiofrequency amplitude response of a 1 Hz dipole placed over a brine-filled rock source (FIG. 1A) and a brine-filled rock source loaded with 50μo of magnetic material (FIG. 1B);
FIG. 2 presents finite-element modeling of the extent of y-axis magnetization in the presence of a simulated 1 mG field generated by a 1 Hz current loop, wherein the magnetic permeability is 1μo (FIG. 2A), 5μo (FIG. 2B), 50μo (FIG. 2C) and 500μo (FIG. 2D);
FIG. 3 presents a 1:30 scale schematic model of the simulated magnetic flux generated in a geological structure through a magnetic well-bore in the absence of injected magnetic material;
FIG. 4 presents a 1:30 scale schematic model of the simulated magnetic flux generated in a geological structure through a magnetic well-bore in the presence of 50μo injected magnetic material; and
FIG. 5 presents finite-element modeling of simulated total magnetization in a horizontal well-bore in the presence of 50μo injected magnetic material as determined by a resonant frequency magnetic detector with offset (FIG. 5A) and non-offset (FIG. 5B) detector configurations.
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In the following description, certain details are set forth such as specific quantities, sizes, etc. so as to provide a thorough understanding of the various embodiments disclosed herein. However, it will be obvious to those skilled in the art that the present disclosure may be practiced without such specific details. In many cases, details concerning such considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present disclosure and are within the skills of persons of ordinary skill in the relevant art.
Referring to the drawings in general, it will be understood that the illustrations are for the purpose of describing particular embodiments of the disclosure and are not intended to be limiting thereto. Drawings are not necessarily to scale.
While most of the terms used herein will be recognizable to those of ordinary skill in the art, the following definitions are nevertheless put forth to aid in the understanding of the present disclosure. It should be understood, however, that when not explicitly defined, terms should be interpreted as adopting a meaning presently accepted by those of skill in the art.
“COMSOL®,” refers to a finite-element modeling (FEM) software package available for various physics and engineering applications (http://www.comsol.com). COMSOL® modeling presented herein includes static and time-varying three-dimensional electromagnetic modeling.
“Ferrite” as defined herein, refers to a ferromagnetic compound formed from iron (III) oxide and another oxide. Illustrative ferrites include materials with a general formula AM2O4, wherein A and M are metal atoms and at least one of A and M is Fe.
“Ferrofluid,” as defined herein, refers to a liquid that becomes polarized in the presence of a magnetic field. A ferrofluid typically includes a paramagnetic, superparamagnetic, ferromagnetic or ferrimagnetic material disposed as a colloidal suspension in a carrier fluid such as, for example, an organic solvent or water. The magnetic material disposed in the carrier fluid can be a magnetic nanoparticle.
“Hematite,” as defined herein, refers to a common mineral form of iron (III) oxide.
“Magnetite,” as defined herein, refers to a ferrimagnetic mineral having a chemical formula Fe3O4.