Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
2001-02-21
2003-11-25
Bagnell, David (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C166S254200, C175S050000, C073S152020
Reexamination Certificate
active
06651739
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to ground penetrating radar and, more specifically, to a preferably digitally controlled transceiver operable to produce and broadcast a pseudo noise code through geological formations at medium frequencies.
2. Description of Prior Art
Ground penetrating radars generally require a carrier frequency of at least 50 MHz in order to provide a useable range resolution. This frequency is too high to penetrate many lithologies of interest. If the carrier frequency is greatly reduced to permit better penetration of the medium, then the bandwidth of the radar must also be reduced. Range resolution is directly related to the bandwidth, thus the resolution becomes poor and the radar may be useless. It would be desirable to provide a system wherein resolution was not dependent on bandwidth so that lower frequency transmission could be used.
Ground imaging radar systems also require system bandwidths much higher than possible in the down-hole environment. Another problem of the prior art is that multiple sensors or moving sensors are generally used for image forming and this is generally not possible or not practical at a subsurface location within a small diameter hole.
Most magnetically based detectors are used for metal detection. Such detectors are not generally useable for detection of downhole formation features and properties such as a water incursion many meters from the instrument because of a lack of sensitivity, poor resolution, and a weak response to water or other interfaces.
One use of a radar that could be transmitted at relatively lower frequencies for detecting formation interfaces would be to detect and locate the movement of approaching water to an oil producing well such as the water incursion caused by water injection that is used to assist in the extraction of oil. The detection of injected water in one or more production zones of the well would permit these sections of the well to be shut down in a timely manner and thereby allow for continued production from other zones of the well. If the water incursion is permitted to flow into the well through only one zone, then production from all zones may typically need to be stopped.
Another use of such a radar concerns a basic problem that has existed in the well logging business for decades, i.e., the effects of invasion that occur prior to running casing. During drilling, the drilling fluid which may be water or oil based is typically weighted to be overbalanced so as to prevent a blowout. The pressure at the formations of interest due to the overbalanced fluid column within the wellbore forces the drilling fluid into the formation and displaces the true formation fluids to produce what is commonly known as invasion. The invaded zone may typically extend into the formation by an amount usually less than about two meters. Because electronic logging tools are attempting to detect and measure the true formation fluids which have been displaced by an undetermined amount of drilling fluid, inaccuracies have, for decades, plagued the logging industry. The standard method for overcoming such inaccuracies is to use two or more sensors of the same or similar type that read different depths into the formation, e.g., dual laterolog tools, dual induction tools, and dual spaced neutron tools and use the difference in readings to correct for invasion. However, due to the unknown amount of change in resistivities, permittivities, electron densities, and so forth caused by the displacement of true formation fluid, and due to partial invasion regions wherein invasion is not complete, inaccuracies caused by invasion may be difficult to resolve. Therefore, it would be highly desirable to provide a downhole logging tool for logging prior to installation of casing that directly measures the depth of invasion to thereby provide a more reliable means for correcting the errors produced in logging tools due to invasion.
U.S. Pat. No. 4,937,580, issued Jun. 26, 1990, to R. H. Wills, discloses a ground probing radar for detecting radar reflections from underground objects. The radar is of the pulse compression type. A transmitter generates a biphase digitally modulated carrier signal. The digital modulations comprise successive pairs of complementary codes. Reflections of the transmitted signal from underground objects are demodulated and cross-correlated with the code words to produce a reflectivity sequence signal. The use of complementary codes results in minimal time sidelobes and improved range and resolution.
U.S. Pat. No. 5,904,210, issued May 18, 1999, to Stump and Allen, discloses an apparatus and method for determining a location and an orientation of an underground boring tool by employment of a radar-like probe and detection technique. The boring tool is provided with a device which generates a specific signature signal in response to a probe signal transmitted from above the ground. Cooperation between the probe signal transmitter at ground level and the signature signal generating device provided at the underground boring tool results in accurate detection of the boring tool location and, if desired, orientation, despite the presence of a large background signal. Precision detection of the boring tool location and orientation enables the operator to accurately locate the boring tool during operation and, if provided with a directional capacity, avoid buried obstacles such as utilities and other hazards. The signature signal produced by the boring tool may be generated either passively or actively, and may be a microwave or an acoustic signal. Further, the signature signal may be produced in a manner which differs from that used to produce the probe signal in one or more ways, including timing, frequency content, information content, or polarization.
U.S. Pat. No. 5,900,833, issued May 4, 1999, to Sunlin and Heger, discloses a ground penetrating impulse radar system providing three-dimensional images of targets. A moving array of transmitting and receiving antennas provides narrow beamwidths and high gain by real and synthetic aperture beam processing. Narrow pulsewidth impulse signals are utilized to obtain high resolution. Round trip time is calculated for each three-dimensional pixel in a search volume, and is used to process three-dimensional imagery. Analog to digital conversion can be utilized, so all signal processing is accomplished digitally. The radar system is applicable in detecting small objects near the surface by using very narrow pulses, and also can be applied to detect large, deep objects by wider pulses.
U.S. Pat. No. 5,869,967, issued Feb. 9, 1999, to Reinhold Straus, discloses a device for the detection of objects lying in the earth which, irrespective of topography, soil structure and state of the terrain, permits high surface yields with great precision in identifying the position of the objects to be detected without endangering the operating personnel. On a mobile device is arranged at least one jib that swivels about a vertical axis, on whose free end are arranged adjacent to each other several measuring heads for sweeping over strip-shaped surface areas of the terrain to be investigated. With the measuring heads on the free end of the jib at least one ground marking device is arranged for distinguishing the find site determined by the measuring heads.
U.S. Pat. No. 5,819,859, issued Oct. 13, 1998 (disclaimed—not to extend beyond the expiration date of U.S. Pat. No. 5,720,354), to Stump and Allen, discloses an apparatus and method for locating an underground object or structure by employment of a radar-like probe and detection technique. The underground structure is provided with a device which generates a specific signature signal in response to a probe signal transmitted from above the ground. Cooperative action between the probe signal transmitter at ground level and the signature signal generating device provided on the underground object provides for accurate detection of the subsurface object, despite the pres
Amini B. Jon
Arndt G. Dickey
Byerly Kent A.
Carl James R.
Bagnell David
Ro Theodore U.
The United States of America as represented by the Administrator
Walker Zakiya
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