Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-07-23
2001-08-14
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S227190, C356S032000, C385S012000
Reexamination Certificate
active
06274863
ABSTRACT:
BACKGROUND OF INVENTION
1. Technical Field
The present invention relates to seismic monitoring or sensing; and more particularly relates to seismic monitoring or sensing using a reconfigurable array.
2. Description of Related Art
A seismic system having distributed selectable fiber optic sensors is known in the art. The seismic system has an optical fiber with fiber optic grating based sensors distributed along a borehole of a well. Each fiber optic grating based sensor has a different wavelength for interrogating a separate fiber optic grating based sensor. The seismic system is not reconfigurable for looking at different groups of fiber optic grating based sensors distributed along a borehole of a well.
Moreover, seismic sensing systems having a hydrophone or geophone array are known that are “ganged” together in groups, also known as levels. This is done for redundancy and to improve the signal-to-noise ratio (S/N). This grouping creates a spatial length over which a seismic measurement can be made. Once hard-wired into a group and deployed, it is not feasible to interrogate the individual elements of the group. To look at an array with a higher spatial resolution capability, one would need to access these separate elements. In a typical seismic survey, a seismic array is defined and built prior to installation. One disadvantage of the related art is that once deployed it is not possible to reconfigure the array.
SUMMARY OF INVENTION
The present invention provides a new and unique seismic sensing device having a light source, detection measuring and processing device in combination with an optical seismic sensor reconfigurable array.
The light source, detection measuring and processing device provides a selective optical signal to the optical seismic sensor reconfigurable array. The light source, detection measuring and processing device also responds to an optical seismic sensor reconfigurable array signal from the optical seismic sensor reconfigurable array, for providing information about a seismic force to be sensed.
The optical seismic sensor reconfigurable array responds to the selective optical signal, and further responds to the seismic force, for providing an optical seismic sensor reconfigurable array signal containing information about the seismic force over different selective lengths of the optical seismic sensor reconfigurable array.
The optical seismic sensor reconfigurable array includes an optical fiber having optical seismic sensors, each including at least one sensor coil arranged between a respective adjacent Fiber Bragg Grating partial reflector pair with a selectable wavelength.
The optical seismic sensor reconfigurable array also includes at least two different groups of optical seismic sensors, each having a different configuration.
The optical seismic sensor reconfigurable array may include a common optical seismic sensor in the at least two different groups. The common optical seismic sensor may include a sensor coil arranged between both a first adjacent Fiber Bragg Grating partial reflector pair having a first selectable wavelength &lgr;
1
and a second adjacent Fiber Bragg Grating partial reflector pair having a second selectable wavelength &lgr;
2
.
sensor coil may include a mandrel having the optical fiber wrapped thereabout.
In operation, the seismic force causes a strain and a change of length of the optical fiber wrapped around the sensor coil between Fiber Bragg Grating partial reflector pairs. The strain or the change of length of the optical fiber causes a change or shift in the phase of light in the fiber coil, providing an interferometric output that is sensed by the light source, detection measuring and processing device.
One advantage of the present invention is that the optical seismic sensor reconfigurable array may be configured and reconfigured to set up the optical seismic sensors for operation in many different configurations or patterns, including variable level configuring, staggered window configuring, array reconfiguring, an array zoom configuring, and a variable apodization spatial array configuring.
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.
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CiDRA Corporation May 1998, “Applications of Optical Fiber Bragg Grating Sensors for the Seismic Industry,” pp. 1-12.
“Fiber Bragg Grating Array Sensor System Using a Bandpass Wavelength Division Multiplexer and Interferometric Detection”,Berkoff et al., IEEE Photonics Technology Letters, US, IEEE Inc., New York, vol. 8, No. 11, Nov. 1, 1996, pp. 1522-1524.
Allen Stephone B.
CiDRA Corporation
Ware Fressola Van Der Sluys & Adolphson LLP
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