Communications – electrical: acoustic wave systems and devices – Seismic prospecting – Well logging
Reexamination Certificate
1994-10-13
2001-02-13
Moskowitz, Nelson (Department: 2202)
Communications, electrical: acoustic wave systems and devices
Seismic prospecting
Well logging
C367S026000, C367S030000, C367S035000, 36
Reexamination Certificate
active
06188643
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to ultrasonic inspection and, more particularly, to a method and apparatus for ultrasonic inspection of pipe, such as transportation pipelines, utility plumbing, and, especially, metal casing in a well bore.
BACKGROUND OF THE INVENTION
Metal casing is commonly used in oil well boreholes, and it is desirable to periodically determine the physical condition and integrity of the casing, which is subject to deterioration, such as from corrosion. Ultrasonic inspection of casing and other piping is known in the art. One type of such equipment is utilized by the assignee of the present application, Schlumberger Technology Corporation, and is called the Ultrasonic Imager (“USI”—trademark of Schlumberger Technology Corporation). In an example of a borehole ultrasonic inspection equipment, a tool is lowered in a cased borehole and has a rotating acoustic transducer that emits a pulse of ultrasonic energy toward the casing. As shown, for example, in U.S. Pat. No. 5,274,604, which relates to characterizing interfaces formed between various materials in a cased borehole, the transducer can be focused. The echoes from the casing are received by the same transducer, and converted to electrical signals by the transducer. The signals can be processed to obtain characteristics of the casing, including its inner radius, reflectivity, and thickness.
An accurate determination of the casing inner radius can be obtained by processing the received echoes using a “center of energy” (“COE”) technique, as described, for example, in Stanke and Liang, “Profiling High-Angle Surfaces With Focused Transducers And Time-of-Flight Measurements”, IEEE 1990 Ultrasonics Symposium, 1990. However, existing techniques of casing thickness determination could stand improvement. The reflected echoes from the casing outer surface tend to be small compared to those from the inner surface. Also, the consistent detection of the arrival of echoes from the casing outer surface can be difficult. When the ultrasound energy first impinges on the casing inner surface, both compressional and shear ultrasonic components propagate toward the casing outer surface, and when some of the energy from these components reflect off the casing outer surface, both compressional and shear components are again generated and propagate back toward the casing inner surface, with energy therefrom being ultimately received by the transducer. Compressional (p) components have a substantially higher velocity than shear (s) components. In general, the casing thickness would be ideally determined from the initial p-p echo [the forward and reflected compressional components, which arrive first]. The p-s and s-p components arrive at the transducer at about the same time and can have a cumulatively greater amplitude than the somewhat earlier p-p arrival. Although the p-p arrival can usually be distinguished from the later arriving p-S/s-p arrivals, the p-p can also be confused with the ringing tail end of the main (first) reflection from casing inner surface. This is particularly true for thin casings and for reflections from casing outer surface pits and other deformities.
Further limitations of existing ultrasonic casing inspection systems relate to their ability to obtain relatively high resolution measurements of casing characteristics at a relatively high rate, and to communicate sufficient information to the earth's surface on a limited bandwidth communications channel.
It is among the objects of the present invention to provide solutions to the above-indicated problems and limitations of the prior art, and to generally improve ultrasonic inspection of casing and other piping.
SUMMARY OF THE INVENTION
In accordance with one feature of the invention, an improved technique is provided for determining the thickness of a member, especially pipe such as fluid-filled casing in an earth borehole. An embodiment of the method includes the following steps: directing a pulse of ultrasonic energy toward the inner surface of the pipe, and receiving and storing, as a function of time, signals representative of ultrasonic energy reflected from the inner surface of the pipe; determining, from the stored signals, the arrival time of the initial echo from the inner surface; determining, from the stored signals, the arrival time and the amplitude of a first candidate initial echo from the outer surface of the pipe; performing a reverse search on the stored signals to determine, from stored signals at times earlier than the arrival time of the first candidate, the arrival time and the amplitude of a second candidate initial echo from the outer surface; comparing amplitudes of the first and second candidates, and selecting, based on the comparison, one of the first and second candidates as the actual outer surface echo; and determining the thickness of the pipe from the arrival time of the actual outer surface echo and the arrival time of the inner surface echo. Using the technique hereof, the earlier arriving candidate can be properly identified as the actual outer surface echo, even when the later arriving candidate has a greater amplitude.
In accordance with a further feature of the invention, weakly focused ultrasound beam pulses are focused on the inner surface of fluid-containing casing in an earth borehole to obtain improved spatial resolution and measurement accuracy in the determination of casing thickness. Preferably, the convergence angle of the beam should not include significant incident energy above the compressional critical angle for the inner casing surface, even when transducer position or casing eccentering or other factors result in focusing that deviates somewhat from the inner surface of the casing. In accordance with an embodiment of the invention there is provided an ultrasonic transducer assembly for transmitting ultrasonic energy through the liquid to the casing and for receiving ultrasonic energy representative of echoes reflected from the casing; the ultrasonic transducer assembly including means for focusing the transmitted ultrasonic energy at the inner surface of the casing, the ultrasound being focused with a focusing cone of f/3 or higher f-number for a typical steel casing in a typical borehole (e.g. about 5 to 13 inch inner diameter); and means for determining the casing thickness from the received echoes.
A further feature of the invention is that casing parameters, particularly inner radius and thickness, can be computed downhole with relatively high spatial resolution, and transmitted to surface equipment for display uphole in real time.
Further features and advantages of the invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3929006 (1975-12-01), Boggs et al.
patent: 4160385 (1979-07-01), Gromlich et al.
patent: 4799177 (1989-01-01), Sarr
patent: 4893286 (1990-01-01), Cobb
patent: 4953147 (1990-08-01), Coff
patent: 5072388 (1991-12-01), O'Sullivan et al.
patent: 5237643 (1993-08-01), Kawabata et al.
Herve Philippe G.
Liang Kenneth K.
Stanke Fred E.
Jeffery Brigitte L.
Moskowitz Nelson
Novack Martin M.
Pojunas Leonard W.
Schlumberger Technology Corporation
LandOfFree
Method and apparatus for inspecting well bore casing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for inspecting well bore casing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for inspecting well bore casing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2576184