Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Reexamination Certificate
2001-03-19
2002-10-15
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
C324S346000, C175S045000
Reexamination Certificate
active
06466020
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates, in general, to a method and apparatus for surveying generally horizontal boreholes below the earth's surface, and more particularly to a system for detecting and precisely locating a drill head in a borehole with respect to a known location, for use in guiding the drilling of the borehole to a specified location.
Horizontal directional drilling techniques are well known, and have long been used to drill boreholes which cross under areas where trenching is not permitted or is impractical. For example, such techniques are used to drill boreholes under manmade or natural obstacles, such as bodies of water, rivers or lakes, and under highways, airport runways, housing developments, or the like. These boreholes may be used, for example, to position pipelines, underground transmission lines, communications lines such as optical fibers, and other utilities, and often must be drilled within defined areas, must travel long distances, and must exit the ground at predetermined locations.
Conventional directional drilling techniques used to drill such boreholes commonly use a steering tool which measures the borehole inclination, azimuth and tool roll angle at each station where measurements are made. The borehole coordinates are computed and tabulated from these steering tool data as a function of the measured distance along the borehole, which may be referred to as the measured depth of the steering tool. These borehole coordinates suffer from serious cumulative effects caused by the inclination and azimuth determinations made at regularly spaced stations along the borehole, and the lateral errors generated by such conventional borehole surveying are intolerable. The inherent imprecision of this integration is the reason for turning to electromagnetic methods for directly determining drill bit location. However, determination of the radial away distance from the entry point to the drill bit is quite precise since a borehole normally changes direction slowly and modestly in both inclination and azimuth along its length. Thus, if a borehole has been following a curved borehole proposal design path, and has not deviated by more than 3 degrees in direction from the design path direction for 500 meters of drilling, the lateral error with respect to that design proposal could be 25 meters, whereas the radial away error would be less than 1 meter. Accordingly, the present invention incorporates the inherent precision of the radial away distance and the use of electromagnetic processes for determining lateral position in order to precisely locate a drill bit.
important aspect of drilling boreholes for pipeline and cable burial projects is the requirement that the borehole exit at the Earth's surface at a precisely determined location. In order to do this, the driller not only must have a direct determination of lateral position, but also needs reaffirmation of the precise radial distance to the exit location at a distance from that exit point so that appropriate adjustments to the inclination of drilling can be made. Even if the radial distance to the exit location from the entry point of the borehole into the Earth is precisely known and the radial distance of the drill bit from its entry point into the Earth is precisely known, safety considerations alone give high priority to directly determining the relative location of the desired borehole exit point with respect to the drill bit location as the exit point is approached. This invention discloses improved methods of guiding the drilling to the required exit location.
A further important concern in drilling is responding to a sudden and unexpected deflection of the borehole by up to several degrees due to hitting boulders or other obstacles. Immediate correction of such a drilling direction perturbation can be more important than immediate correction of a displacement error since such direction perturbations can lead to a tortuous borehole, which is a very serious defect particularly when attempting to pull a pipeline through the completed borehole. Steering tool inclinometers provide good inclination measurements, usually to a precision of 0.1 or 0.2 degrees; thus good control exists in inclination. However, the standard steering tool azimuthal direction determination provided by the Earth Field magnetometers is inadequate. In addition to being intrinsically much less precise than the inclinometers because of steel in the drill string, motor and drill bit, they are also subject to sudden environmental changes from steel and magnetized objects in the vicinity of the borehole and by nearby auto, truck, train, and ship traffic. This invention provides a much needed method and an apparatus for measuring drilling direction perturbations.
A variety of attempts to improve the accuracy of underground drilling have been made. One such attempt included the use of grids on the earth's surface to guide the drill head, but if access to the surface is not available along the length of the borehole, this technique can encounter serious problems. For example, electrical current-carrying surface grids may be placed on both sides of a river, but since such grids have a limited range, they may not be effective if the borehole drifts away from its planned path as it travels from one grid to the other. Other attempts have included the use of two-loop antenna systems for generating two fields with different frequencies, which are measured by magnetometers mounted within the drill head. Still other attempts to provide improved drill guidance include the use of an externally generated magnetic field produced by one or more current loops made up of straight line segments, wherein the fields are measured by a probe at the drill, the probe having three orthogonal magnetometers which measure X, Y and Z components of the magnetic field. Three accelerometers measure the rotation of the probe with respect to gravity, and this data is used to determine the magnetic field vector at the magnetometers. A theoretical magnetic field vector is then calculated and compared to the measured vector to determine the location of the probe.
Although some of these prior systems have been adequate for many applications, they have not been totally satisfactory, and there exists a need for an improved borehole surveying method which will permit accurate and reliable location of drill heads for drill heads to enable boreholes to be drilled along preselected paths to distant locations.
SUMMARY OF THE INVENTION
In accordance with preferred embodiments of the invention, improved methods for precisely surveying the path of a borehole in the Earth are provided. These methods are not only used to locate a drill head and its steering tool in a borehole in order to provide data for guiding the drilling of the borehole along a prescribed path, for example to an exit point at a remote location, but may also be used for other purposes such as surveying existing boreholes.
The method of the present invention is based on the use of a detector which may be adapted from, or which may be similar to, those which are found in conventional steering tools for drill assemblies. In a preferred form of the invention, the detector incorporates two single-axis electromagnetic field sensors which preferably are perpendicular to each other and to the axis of the steering tool, and lie on an imaginary “patch”, or segment on the surface of a sphere. The sensors are approximately perpendicular to the radius of this spherical segment, with the radius being centered at a fixed location from which measurements are to be made; for example, at the entry point of a borehole being drilled into the Earth. One or more guide wires are located on the Earth's surface near the borehole entry point and/or the borehole exit point, and extend along the surface above the prescribed borehole path. An electromagnetic field is generated in the Earth in the region of the prescribed path by a known electric current flowing through the guide wires. Values of x an
Kuckes Arthur F.
Pitzer Rahn
Susmann Herbert J.
Jones Tullar & Cooper P.C.
Kinder Darrell
Lefkowitz Edward
Vector Magnetics LLC
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