Abstract: An apparatus and method for surveying the path of a borehole includes two single-axis field sensors located at a radius centered at a fixed location. Guide wires are located along the earth's surface above the prescribed borehole path and the known electromagnetic field produced by current in the guide wires are detected by the sensors. Values of X and Y vectors at multiple locations on a spherical surface at the radial distance of the sensors are calculated and compared with measured values to define the location of the sensors on the spherical surface to permit the lateral spacing between the sensors and the desired borehole path to be determined.

Abstract: A directional drilling control system for a drill stem carrying a conventional drilling head includes an elongated actuator housing fixed in a borehole being drilled. The drill stem passes through the housing and is generally coaxial with it, and an actuator within the housing is selectively activated to deflect the drill stem with respect to the axis of the housing. The actuator is selectively driven to regulate the direction and amount of deflection to thereby control the direction of drilling. An electrical controller in the housing in communication with a surface controller and/or with feedback sensors in the housing controls the actuator.

Abstract: A method and apparatus for precise measurement of the distance and direction from a magnetic field sensor to a nearby magnetic field source includes an elongated iron core solenoid driven by a repetitive, nonsinusoidal current source. In the near field the solenoid has two spaced, temporally varying magnetic poles, and measurement of the distance and direction to this source includes analysis of field components which vary in synchronism with the current source.

Abstract: A method and apparatus for steering boreholes for use in creating a subsurface barrier layer includes drilling a first reference borehole, retracting the drill stem while injecting a sealing material into the Earth around the borehole, and simultaneously pulling a guide wire into the borehole. The guide wire is connected to a source of current to produce a corresponding magnetic field in the Earth around the reference borehole while an adjacent borehole is drilled. The vector components of the apparent Earth's magnetic field are measured vectors are used to determine the distance and direction from the borehole being drilled to the reference borehole in order to steer the borehole being drilled. The process is repeated to provide multiple parallel subsurface boreholes with adjacent boreholes being spaced sufficiently close together to insure overlapping of the sealing material to produce a continuous barrier.

Abstract: A borehole guidance system for guiding a well being drilled with respect to an existing reference well includes a multi-sectioned casing in the reference well. A selected section of the casing, usually the lowest section, is electrically conductive and the next adjacent section is electrically nonconductive. A wireline connects a current source on the surface to the selected conductive section to produce a reference current in the well. The reference current is injected into the earth and dissipated so that the current produces a reference magnetic field surrounding the well which is unaffected by return currents.

Abstract: A single guide wire system for use in continually directional drilling of boreholes, includes a guidewire extending generally parallel to the desired path of the borehole. The guidewire is connected at a first end to one side of a reversible source of direct current, and at a second end to ground. A second side of the DC source is also connected to ground. A known current flow in a first direction for a first period of time and in a second direction for a second period of time produces corresponding static magnetic fields in the region of the borehole. The vector components of the fields are measured in the borehole by a 3-axis magnetometer, and from these vector components the effects of the Earth's magnetic field are canceled and the distance and direction from the borehole to the guidewire are determined. These values permit control of further drilling of the borehole along a desired path.

Abstract: A method for determining the distance and direction from a first borehole to a second borehole includes generating, by way of a rotating magnetic field source at a first location in a second borehole, and elliptically polarized magnetic field in the region of the first borehole. First and second sensors positioned at an observation point in the first borehole measure the amplitude and relative phase of respective first and second components of the polarized magnetic field and from these measurements, the direction, relative to the sensors, from the observation point to the first location is determined. The distance between these points is determined by measuring at plural observation points amplitude variations with depth of the rotating magnetic field in the first borehole, and computing theoretical variations in the amplitude for different assumed distances between the observation points and the location of the magnetic field source.

Abstract: A single guide wire system for use in continually directional drilling of boreholes, includes a guidewire extending generally parallel to the desired path of the borehole. The guidewire is connected at a first end to one side of a reversible source of direct current, and at a second end to ground. A second side of the DC source is also connected to ground. A known current flow in a first direction for a first period of time and in a second direction for a second period of time produces corresponding static magnetic fields in the region of the borehole. The vector components of the fields are measured in the borehole by a 3-axis magnetometer, and from these vector components the effects of the Earth's magnetic field are canceled and the distance and direction from the borehole to the guidewire are determined. These values permit control of further drilling of the borehole along a desired path.

Abstract: A method and apparatus for drilling a borehole under an obstacle including placing a solenoid on the surface of the earth at the far side of the obstacle, near a preselected borehole exit location. A drilling assembly at an entry location on the near side of the obstacle is driven to produce a borehole which is directed under the obstacle toward the exit location. Initially, guidance of the drilling assembly is by conventional survey techniques, but when the borehole moves to within about 100 meters of the solenoid, the solenoid magnetic field is used to guide the drilling operation.

Abstract: A method and apparatus for determining the distance and direction to a borehole containing ferromagnetic material includes placing a sensor package in a second nearby borehole and measuring three vector components of the static magnetic field perturbations of the earth's magnetic field caused by the ferromagnetic material. The sensor package is moved within the second borehole to obtain a plurality of magnetic field measurements, and the measured components are then projected onto a system of fixed coordinates whose orientation in space is known. The relative direction from the second borehole to the first is determined from the vector components, and the magnitude of the resultant in the direction of the first borehole is then determined from the fixed coordinate system.In a modification, the sensor package includes two spaced magnetometers for measuring vector components of the magnetic field perturbations.

Abstract: Methods for determining the distance from a borehole to a nearby, substantially parallel target well for use in guiding the drilling of the borehole, including positioning a magnetic field sensor in the borehole at a known depth and providing a magnetic field source in the target well. The wells may be vertical or horizontal, and the source preferably is a solenoid movable in the target to a location at approximately the same depth as that of the sensor.The distance between the borehole and the solenoid is determined, in one embodiment, by moving the solenoid to depths above and below the depth of the sensor, and detecting maximum field vectors. The distance the solenoid moves between the maxima is the distance between the wells. In another embodiment, the ratio of solenoid magnetic field vectors is used to determine the ratio of the difference in depth z between the solenoid and the sensor to the lateral distance R between the wells. This ratio z/r is then used to determine the separation of the wells.

Abstract: Apparatus for measuring magnetic fields while drilling includes an electrode located adjacent or in contact with a target well casing to produce an electrical current. The current including a fundamental wave component having two opposite zero crossings per cycle and an even harmonic wave component having two opposite zero crossings per cycle produces an alternating current magnetic field in the earth surrounding the target well. The target well is to be intercepted by, or to be avoided by, a relief well being drilled.

Abstract: Magnetic field gradient sensing apparatus utilizing highly sensitive fluxgate magnetometers permit direct determination of the distance between two well bores and for determining the direction from one bore to the other. The gradient sensing apparatus may be responsive to alternating magnetic fields resulting from current flow in a steel casing within a target well and measured by two fluxgate magnetometers diametrically oppositely located in a sensor tool and oriented to measure the vector components of the alternating field at opposite sides of the tool to thereby obtain a measure of the gradient of the field across the diameter of the tool. Field gradient sensing apparatus may also be used to measure the gradient of a static magnetic field having a radial gradient, wherein the static field is produced by ferromagnetic materials in the target well. Again, a pair of magnetometers is utilized to measure the field gradient across the diameter of the sensor to determine distance and direction to the target.

Abstract: A magnetic field guidance system for guiding a movable carrier such as a drill assembly with respect to a fixed target includes a pair of magnetic field sources at one location, such as the carrier, and a highly sensitive magnetic field detector at the other location, or target. The first field source is driven by an alternating current to produce a low frequency alternating axial field, while the second source is a magnet which produces a field perpendicular to the axis of the first field. Where the magnetic field sources are mounted on a rotatable drill assembly, the second source may be a permanent magnet which rotates with the drill assembly. The detector may be a fluxgate magnetometer which senses the direction of the target location with respect to the direction of the axial field by determining the deviation from perpendicular of the two magnetic fields at the target location.

Abstract: A method and apparatus for determining the distance from a relief borehole to a target well utilizes measurements of an electric field at the target well. The electric field is produced by injecting current into the earth near the wellhead of the target well, this current producing a target current in conductive material in the target well. The electric field corresponding to the target current is measured by means of sensors in the relief borehole, and this field measurement, together with a measurement of the alternating magnetic field at the relief well due to the target current, permits determination of the distance to the target well from the relief borehole.

Abstract: A method for guiding a borehole with respect to a target wireline carrying low frequency alternating current is disclosed. A wireline carrying an electrode at its terminal end is positioned in a target cased or uncased borehole with the electrode contact the wall of the borehole. An AC source is connected between the wireline and ground to supply current to the borehole wall near the bottom of the borehole. A sensor is positioned in a borehole being drilled to sense the magnetic field generated by current flow in the wireline, the sensor being spaced sufficiently far along the wireline from the electrode location to prevent magnetic fields due to return current through the target borehole casing on through the ground surrounding the target borehole from significantly affecting the sensor. The sensor measures the net alternating magnetic field to determine the direction to the target borehole, to permit guidance of the borehole drilling.

Abstract: A method and apparatus for determining the distance and direction of a well from a borehole. A toroidal inductor surrounds a drill stem within a borehole. The inductor acts as a primary for a transformer, with the drill stem, the earth surrounding the borehole, and electrically conductive material at the target well forming a single loop transformer secondary. An oscillator is connected to the primary to produce an induced AC current in the secondary. Secondary current flowing in the target well produces an AC secondary magnetic field which is detected at the borehole.

Abstract: A system for measuring X and Y vector components of a composite magnetic field including static portions such as those produced by the earth's magnetic field, and time varying portions such as those produced by current flowing in a target anomaly to thereby permit determination of the distance and direction from a sensor to the anomaly is disclosed. Highly sensitive fluxgate magnetometers sense total field X and Y axis vector components of the composite magnetic field of interest and produce output signals which are fed through corresponding detector and null circuits to produce total field signals corresponding to the components being measured. These total field component signals are fed through corresponding signal conditioning circuits to equalize the time varying and static field portions of the signal components.

Abstract: A method of locating, from a relief well, a target borehole of a deep well at a substantial distance below the earth's surface, while approaching the target borehole at a large angle of intersection. A homing tool incorporating a magnetic field sensor having its axis of maximum sensitivity parallel to the axis of the relief well detects an A.C. magnetic field produced by alternating current in the target borehole to provide the data required for directing further drilling of the relief well.

Abstract: Methods for determining the distance from a borehole to a nearby, substantially parallel target well for use in guiding the drilling of the borehole, including positioning a magnetic field sensor in the borehole at a known depth and providing a magnetic field source in the target well. The wells may be vertical or horizontal, and the source preferably is a solenoid movable in the target to a location at approximately the same depth as that of the sensor.The distance between the borehole and the solenoid is determined, in one embodiment, by moving the solenoid to depths above and below the depth of the sensor, and detecting maximum field vectors. The distance the solenoid moves between the maxima is the distance between the wells. In another embodiment, the ratio of solenoid magnetic field vectors is used to determine the ratio of the difference in depth z between the solenoid and the sensor to the lateral distance R between the wells. This ratio z/r is then used to determine the separation of the wells.