Communications: electrical – Wellbore telemetering or control – Using a specific transmission medium
Reexamination Certificate
2000-07-28
2004-02-24
Edwards, Timothy (Department: 2635)
Communications: electrical
Wellbore telemetering or control
Using a specific transmission medium
C340S870310, C324S534000, C324S535000
Reexamination Certificate
active
06696974
ABSTRACT:
FIELD OF INVENTION
This invention relates to the improvement of event detection capabilities for cable monitoring devices utilizing time domain reflectometry principles as installed in geotechnical materials.
BACKGROUND
Time Domain Reflectometry, or TDR, is a remote sensing electrical measurement technique that has been used for many years to determine the spatial location and nature of various objects. An early form of TDR, dating from the 1930s, that most people are familiar with is radar. The type of TDR most commonly referred to by the acronym in the industry is coaxial TDR. Coaxial TDR is essentially a “closed circuit radar”. It involves sending an electrical pulse along a coaxial cable and using an oscilloscope to observe the echoes returning back to the input. This technique was reported in the literature in the 1930's and 40's for testing telephone coaxial cables. Numerous TDR articles and books have been written on the subject since.
Optical TDR functions by sending a light pulse down a fiber optic cable. This pulse is reflected by broken ends or attenuated by cable bends. Sonar, also a type of TDR, operates by pulsing a sound wave through a media and examining the returned echo for reflection and attenuation compared to the original signal.
TDR has been actively investigated by both government and private enterprise for uses in monitoring mining induced displacements in the geologic mass surrounding the mine. U.S. Bureau of Mine research was started in the 1960's, when TDR was primarily used to locate breaks in electrical power cables. Since then, use of the method has expanded, but has still not reached its full potential in the field.
If a geologic material is subject to excess stress, whether generated by natural events (excess rainfall, earthquakes, etc.), or by human events (excavation) it displaces to equilibrate this excess stress. This will result in discrete displacement (failure along a plane) or distributed displacement within the geologic mass. TDR cable monitoring is generally conducted by placing a TDR capable cable in a drill hole in the geologic mass. Prior to installation, the cable may be crimped to provide reference reflections in the cable at known physical locations in the rock mass. After crimping, the cable is inserted into a borehole, and bonded to the surrounding rock with a cement grout. At locations where progressive geologic movement is sufficient to fracture the grout, cable deformation occurs that can be monitored with a TDR cable tester.
This technique has been tested at Syncrude in Canada, amongst other locations. Syncrude operates an oil sand mine in northern Alberta, Canada. The oil sand is mined by large draglines, which operate adjacent to the edge of a highwall that varies in height from 40 to 60 m. Coaxial cables were installed in vertical holes at three highwall locations in the immediate vicinity (less than 10 m) of slope inclinometers so that a comparison could be made between the two types of instrumentation. The objective of these installations was to assess the ease or difficulty of installation, suitability to field conditions, ease or difficulty of data acquisition, comparison with existing monitoring procedures, and sensitivity of TDR to slope movements.
In addition to the field study, an extensive laboratory test program was implemented to correlate TDR reflection magnitude with shear deformation of grouted cables.
It was concluded that TDR represented a promising technology for slope monitoring, but modifications would be required to increase its sensitivity in oil sands and stiff clay soils. Applications in hard rock mining, such as block caving, indicate that block displacement is sufficiently discrete to shear the cable at distinct points, giving a better response than would be expected in stiff clays. In addition, proper selection of the type of cable to be encapsulated, as well as the encapsulation material, such as stiffer grout, can be utilized to increase the system sensitivity to displacement.
It is further known that “crimps” or buttons can be placed on the monitoring cable prior to installation. These impart a manufactured defect in the cable that serves as a reference point for any adjacent TDR reflections. These crimps are not anchors and serve exclusively as reference points for TDR measurement.
In addition, the art in the field of TDR geotechnical monitoring has become almost exclusively focused on the magnitude and type of displacement within the geologic material being monitored. The invention described herein focuses, alternatively, on maximizing the probability of detecting any significant displacement within the geologic material. While the former may be of significance for exact definition of a known feature, or precisely determining the type of failure that may be occurring, within the geologic medium, it lacks sensitivity regarding the specific questions “Is displacement occurring in the geologic material being monitored?” and “If so, where, approximately, is the displacement occurring?” These two questions are of utmost criticality in determining further action and monitoring in any geotechnical monitoring situation. If a slope containing a gas pipeline is failing, a simple, effective monitoring system should indicate immediately that action is required based on the fact that some event is occurring in the geologic material composing the slope, a fact that the proposed invention capitalizes on. The invention proposed herein increases the sensitivity of the geotechnical monitoring system such that it can answer such questions quickly, with more sensitivity, more inexpensively, and with less technical input than the monitoring systems utilized to date.
Little attempt has been made to address the shortcomings of TDR applications mentioned above from the Syncrude report, i.e. modifications are necessary to increase TDR sensitivity in oil sands (sands) and stiff clay soils. The response has generally been to install more sensitive cables utilizing the same old techniques. Thus, TDR monitoring is under-utilized in areas composed of such materials.
The prior art, in terms of sensor cables and cable anchor devices, suffers from a number of flaws:
(a) anchor devices for cables of the prior art are designed for attaching cables to a surface for transmission purposes. As such they are not designed for, and are not applicable, to restricting cable motion in a three-dimensional solid for monitoring purposes.
(b) anchor devices for cables of the prior art are not designed for being encapsulated in a surrounding media such as grout, which is a requirement for geotechnical monitoring.
(c) anchor devices for cables of the prior art are not designed to function in terms of displacement amplification at the end of oblong anchors due to rotation about the anchor's centroid.
(d) with minor exception, the concept of an anchor system being attached to a sensor cable for point strain monitoring, event detection, or continuous strain monitors has been totally ignored.
(e) prior art anchor devices are all too expensive and unnecessarily cumbersome for geotechnical use in light of the number of such devices required for a single sensor cable installation.
(f) most of the existing sensor cable arrangements attempt to quantify the magnitude of displacement between two pre-determined, fixed points along the sensor cable length. This would be unrealistic for geotechnical monitoring as the actual location of a failure surface, i.e., a point to be monitored, is unknown upon installation of the sensor in undisturbed material. For initial analysis, it is the occurrence and approximate location of the failure (deformation) that is critical to the success of geotechnical monitoring, not the absolute deformation magnitude.
(g) the sensor cable devices of the prior art require a specific loading mode. This is generally induced by tension or compression (buckling). Such limitations are too constraining and unnecessary for an event detecting geotechnical monitoring system. If such absolute constraints a
Edwards Timothy
Law Office of Marc D. Machtinger, Ltd.
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