Optical electric field sensors having passivated electrodes
First Claim
1. A permanent electromagnetic (EM) monitoring system that comprises:
- a casing string positioned inside a borehole penetrating a formation;
an optical fiber attached to the casing string;
at least two passivated electrodes on the casing string to provide a potential difference in response to an electric field in said formation;
an electro-optical transducer coupled to the optical fiber to modify a property of light conveyed by the optical fiber in accordance with the potential difference, wherein the electro-optical transducer includes an electrostrictive element that receives the potential difference and responsively alters a tension in said fiber to modify a phase of said light; and
an interface unit that senses said property of said light to measure the electric field.
2 Assignments
0 Petitions
Accused Products
Abstract
Permanent electromagnetic (EM) monitoring of the regions around and between wells may employ a casing string positioned within a borehole through the subsurface formations of interest. At least two passivated electrodes are mounted on the casing string to sense electric fields in the formation. Though only capacitively coupled to the formation, the passivated electrodes nevertheless provide a potential difference to an electro-optical transducer, which in turn modifies a property of the light passing along an optical fiber attached to the casing string. An interface unit senses the modified property to derive a measure of the electric field between each pair of passivated electrodes. The passivated electrodes have a contact surface that is conductive but for one or more layers of non-reactive (and thus electrically insulating) materials. Illustrative materials include metal oxides, polymers and ceramics, but the layers are preferably kept very thin to maximize the coupling capacitance with the formation.
98 Citations
16 Claims
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1. A permanent electromagnetic (EM) monitoring system that comprises:
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a casing string positioned inside a borehole penetrating a formation; an optical fiber attached to the casing string; at least two passivated electrodes on the casing string to provide a potential difference in response to an electric field in said formation; an electro-optical transducer coupled to the optical fiber to modify a property of light conveyed by the optical fiber in accordance with the potential difference, wherein the electro-optical transducer includes an electrostrictive element that receives the potential difference and responsively alters a tension in said fiber to modify a phase of said light; and an interface unit that senses said property of said light to measure the electric field. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A permanent EM monitoring method that comprises:
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running a casing string into a borehole, the casing string including an array of electro-optical transducers coupled to an optical fiber, each electro-optical transducer modifying a property of light conveyed by the optical fiber in accordance with an electrical field sensed by two passivated electrodes capacitively coupled to a formation, wherein the electro-optical transducer includes an electrostrictive element that receives the potential difference and responsively alters a tension in said fiber to modify a phase of said light; coupling the optical fiber to an interface unit; interrogating the array of electro-optical transducers to measure the electrical fields. - View Dependent Claims (10, 11, 12, 13)
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14. A permanent optical electric field sensor that comprises:
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an optical fiber; two leads that electrically connect to two passivated electrodes that provide a capacitive coupling to a formation; and an electro-optical transducer that modifies a property of light conveyed by the optical fiber in accordance with a potential difference between the two leads, wherein the electro-optical transducer includes an electrostrictive element that receives the potential difference and responsively alters a tension in said fiber to modify a phase of said light. - View Dependent Claims (15, 16)
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Specification