Abstract: Electromagnetic field monitoring methods and systems for obtaining data corresponding to subsurface rock formations. An electromagnetic field monitoring system includes an electromagnetic transmitter located downhole in a well bore and configured to radiate electromagnetic radiation into a subsurface formation; a fiber optic cable coupled with a fiber optic interrogator, the at least one fiber optic cable and the interrogator located at the surface; and an array of electromagnetic sensors integrally formed in the fiber optic cable and configured to detect the electromagnetic radiation radiated through the subsurface formation. A method of detecting electromagnetic radiation at the surface of an oil well includes transmitting, from an electromagnetic transmitter, electromagnetic radiation into a subsurface formation; and sensing, from the subsurface formation, electromagnetic radiation at the surface of the oil well.

Abstract: A through-casing formation monitoring system may include a casing string positioned within a wellbore, a power source electrically coupled to a first transmitter configured to produce a magnetic field, a magnetic induction sensor positioned within the casing string such that the magnetic induction sensor allows a continued operation of the wellbore, a fiber optic cable coupled to an electro-optical transducer within the magnetic induction sensor, and an optical interrogation system configured to receive measurements from the magnetic induction sensor via the fiber optic cable.

Abstract: A method of monitoring electromagnetic properties of a subsurface formation may include: obtaining a resistivity distribution in the subsurface formation; identifying sensor positions along a borehole; determining an effective resistivity of each region around a sensor position; deriving from the effective resistivities of regions associated with each sensor position an optimum resonance frequency; tuning an array of sensors to provide each sensor with the optimum resonance frequency; deploying the sensor array in the borehole; and collecting electromagnetic field measurements. Each sensor may include: a coil antenna positioned in a subsurface formation having a resistivity, the coil antenna generating a induced voltage signal from an electromagnetic field in the subsurface formation; and a resonant modulation circuit that converts the induced voltage signal into a telemetry signal, the resonant modulation circuit having a resonance frequency optimized for said formation resistivity.

Abstract: A method of monitoring a substance in a well can include disposing at least one optical electromagnetic sensor and at least one electromagnetic transmitter in the well, and inducing strain in the sensor, the strain being indicative of an electromagnetic parameter of the substance in an annulus between a casing and a wellbore of the well. A system for monitoring a substance in a well can include at least one electromagnetic transmitter, and at least one optical electromagnetic sensor with an optical waveguide extending along a wellbore to a remote location, the sensor being positioned external to a casing in the wellbore.

Abstract: A formation monitoring system includes a casing that defines an annular space within a borehole. A distributed magnetomotive force sensor is positioned in the annular space and configured to communicate with the surface via a fiber-optic cable. A computer coupled to the fiber-optic cable receives measurements and responsively derives the location of any fluid fronts in the vicinity such as an approaching flood front to enable corrective action before breakthrough. A formation monitoring method includes: injecting a first fluid into a reservoir formation; producing a second fluid from the reservoir formation via a casing in a borehole; collecting magnetic field measurements with a distributed magnetomotive force sensor in an annular space between the casing and the borehole, communicating measurements to a surface interface via one or more fiber-optic cables; and operating on the measurements to locate a front between the first and second fluids.

Abstract: A magnetic field sensor unit for a downhole environment includes an optical fiber, a magnetic field sensor, and an optical transducer. The sensor unit also includes a sealed housing that encloses the magnetic field sensor and the optical transducer. The optical transducer is configured to generate a light beam or to modulate a source light beam in the optical fiber in response to a magnetic field sensed by the magnetic field sensor. Related magnetic field measurement methods and systems deploy one or more of such magnetic field sensor units in a downhole environment to obtain magnetic field measurements due to an emitted electromagnetic field.

Abstract: Methods and systems of electromagnetic sensing in a wellbore are presented in this disclosure for monitoring annulus fluids and water floods. An array of transmitters and one or more receivers are located along a casing in the wellbore. A transmitter in the array and one of the receivers can be mounted on a same collar on the casing forming a transmitter-receiver pair. The receiver can receive a signal originating from the transmitter and at least one other signal originating from at least one other transmitter in the array, wherein the signal is indicative of a fluid in the wellbore in a vicinity of the transmitter-receiver pair and the at least one other signal is indicative of another fluid in a formation around the wellbore. The receiver can further communicate, via a waveguide, the signal and the at least one other signal to a processor for signal interpretation.

Abstract: A system, in some embodiments, comprises: a fiber optic cable; first and second sensors to control a length of said cable; and first and second receiver coils that control the first and second sensors, respectively, wherein the first and second sensors maintain said length when the first and second receiver coils receive only a direct signal from a transmitter, wherein the first and second sensors modify said length when the first and second receiver coils receive a scattered signal from a formation.

Abstract: Reelable sensors arrays are independently fabricated separate from a downhole tubular. The sensor arrays are then reeled together onto a spool. At the well site, the sensor array is unreeled from the spool and attached to the tubular as it is deployed downhole, resulting in a fast and efficient method of sensor deployment.

Abstract: Electromagnetic (EM) measurement systems and methods for a downhole environment are described herein. An example system includes an optical fiber, an EM source to emit an EM field, and a magnetic induction sensor. The magnetic induction sensor comprises a coil and an electro-optical transducer coupled to the coil and the optical fiber. The electro-optical transducer generates a light beam or modulates a source light beam in the optical fiber in accordance with a voltage induced in the coil by the EM field.

Abstract: An electric field sensing system comprises a magnetic shield, an optical magnetometer shielded from external magnetic fields by the magnetic shield, a conductive coil proximate to the optical magnetometer, and first and second electrodes coupled to opposite ends of the coil. The electrodes are disposed outside of the magnetic shield. The conductive coil generates a magnetic field within the optical magnetometer when electrical current passes through the conductive coil.

Abstract: A disclosed subsurface electromagnetic field monitoring system includes at least one fiberoptic cable to optically communicate measurements from an array of electromagnetic field sensors in a borehole. The array of electromagnetic field sensors includes a distributed feedback fiber laser strain sensor with electromagnetic field sensitivity.

Abstract: Electromagnetic field monitoring methods and systems for obtaining data corresponding to subsurface rock formations. An electromagnetic field monitoring system includes an electromagnetic transmitter located downhole in a well bore and configured to radiate electromagnetic radiation into a subsurface formation; a fiber optic cable coupled with a fiber optic interrogator, the at least one fiber optic cable and the interrogator located at the surface; and an array of electromagnetic sensors integrally formed in the fiber optic cable and configured to detect the electromagnetic radiation radiated through the subsurface formation. A method of detecting electromagnetic radiation at the surface of an oil well includes transmitting, from an electromagnetic transmitter, electromagnetic radiation into a subsurface formation; and sensing, from the subsurface formation, electromagnetic radiation at the surface of the oil well.

Abstract: A disclosed formation monitoring system includes a casing that defines an annular space within a borehole. A distributed magnetomotive force sensor is positioned in the annular space and configured to communicate with the surface via a fiber-optic cable. A computer coupled to the fiber-optic cable receives said measurements and responsively derives the location of any fluid fronts in the vicinity such as a an approaching flood front to enable corrective action before breakthrough. A disclosed formation monitoring method includes: injecting a first fluid into a reservoir formation; producing a second fluid from the reservoir formation via a casing in a borehole; collecting magnetic field measurements with a distributed magnetomotive force sensor in an annular space between said casing and said borehole, communicating measurements to a surface interface via one or more fiber-optic cables; and operating on said measurements to locate a front between the first and second fluids.

Abstract: A system, in some embodiments, comprises: a fiber optic cable; first and second sensors to control a length of said cable; and first and second receiver coils that control the first and second sensors, respectively, wherein the first and second sensors maintain said length when the first and second receiver coils receive only a direct signal from a transmitter, wherein the first and second sensors modify said length when the first and second receiver coils receive a scattered signal from a formation.

Abstract: Systems and methods for formation evaluation and reservoir monitoring that use electromotive force measurements. A well monitoring system may comprise: a power supply that generates an electromagnetic field in a subterranean formation; and a distributed electromotive force sensor for measuring electromotive force at one or more points along a length of the distributed electromotive sensor, wherein the distributed electromotive force sensor comprises an optical waveguide and an electro-optical transducing layer coated on one or more lengths of the optical waveguide.

Abstract: A method and apparatus for magnetic sensing is described. The apparatus includes a strain-sensing fiber coupled to a conducting strip. The strain-sensing fiber may be, for example, a distributed feedback fiber with Bragg gratings. A current may be induced to flow on the conducting strip by electrically coupling a photodiode to the conducting strip and then activating a laser optically coupled to the photodiode. In the presence of a magnetic field, a Lorentz force will be exerted on the conducting strip, causing a displacement of the conducting strip that will induce strain on the strain-sensing fiber. The strain on the strain-sensing fiber may be measured by laser-pumping the strain-sensing fiber and measuring the reflected waves. The measured strain may be used to calculate the magnitude of the magnetic field. Multiple strain-sensing fibers may be optically coupled in series and deployed into a borehole for distributed magnetic field measurements.

Abstract: Method and apparatus are disclosed for use of a fiber-optic sensor loop for use within a wellbore; with a plurality of light sources optically coupled to the fiber-optic sensor loop; at least one electromagnetically sensitized region within the fiber-optic sensor loop; and a plurality of detectors optically coupled to the fiber-optic sensor loop; and using the sensing system to detect changes in a magnetic field within the wellbore.

Abstract: Reelable sensors arrays are independently fabricated separate from a downhole tubular. The sensor arrays are then reeled together onto a spool. At the well site, the sensor array is unreeled from the spool and attached to the tubular as it is deployed downhole, resulting in a fast and efficient method of sensor deployment.

Abstract: Methods and systems of electromagnetic sensing in a wellbore are presented in this disclosure for monitoring annulus fluids and water floods. An array of transmitters and one or more receivers are located along a casing in the wellbore. A transmitter in the array and one of the receivers can be mounted on a same collar on the casing forming a transmitter-receiver pair. The receiver can receive a signal originating from the transmitter and at least one other signal originating from at least one other transmitter in the array, wherein the signal is indicative of a fluid in the wellbore in a vicinity of the transmitter-receiver pair and the at least one other signal is indicative of another fluid in a formation around the wellbore. The receiver can further communicate, via a waveguide, the signal and the at least one other signal to a processor for signal interpretation.