Abstract: In one aspect a method of determining direction east is provided that in one embodiment includes dropping objects under influence of gravity, determining locations where the objects drop, and determining the direction east from the locations where the objects drop.
Abstract: An apparatus for determining the orientation of a borehole at a point along the borehole, includes a tiltmeter for measuring the inclination of the borehole relative to the vertical, a vector magnetic sensor for measuring the amplitude of the component of the Earth's magnetic field along the axis of the borehole, and means for computing the orientation of the tubular sonde from the measurements of inclination and amplitude of the component of the Earth's magnetic field aligned with axis of the sonde.
Abstract: A method and apparatus is disclosed for improving the accuracy of directional surveys using magnetometers and accelerometers. The method corrects errors in bias, scale-factor, misalignment of cross-axial magnetometers, and bias or scale-factor of axial magnetometer by requiring the magnitude of measured cross-axial magnetic field to be as constant as possible over several tool face angles at a survey point in a wellbore and the magnitude of the measured total magnetic field and dip angle equal to the reference values, respectively. The axial component of the measured magnetic field is also determined. The method also corrects accelerometers similarly. The calibration parameters obtained at one survey point are applied to measurements at other survey points to improve the accuracy of surveys and the efficiency of drilling operations.
Abstract: A magnetic observatory device is deployed at a fixed location such as the sea bed to provide data measuring variations in the local earth magnetic field. This data is used to correct information from magnetic direction sensors, for example in a measurement-while-drilling system of a drill string. Also described is a reference apparatus for initial calibration of the device or for marine magnetic mapping purposes.
Abstract: A devised tilt meter detects tilt of the receptacle installed in the ground and/or in the solid construction, to detect the displacement of a pendulum suspended by thin metal springs. A cavity exists near the middle of the receptacle with a pendulum, the springs, a detector along the lateral side of the receptacle of the tilt meter. Wires for signal and power lines of other tilt meter are easily passed through this cavity. This mechanism with a cavity near the middle of the receptacle is very useful for an array observation of tilt in the ground and/or in a solid construction.
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 miniaturized electronic magnetic compass system, or the like, is mounted in a substantially cylindrical gimbal ring unit of about 0.75 in diameter, and 1.25 in length. Critical to the small size is the pendulum that positions the internal magnetic detector by gravity relative to the earth's surface. Thus, a pendulum formed of tungsten has its curved bottom surface formed of a central spherical surface and two flanking cylindrical surfaces meeting in two planes disposed at an angle intersecting with the pendulum axis of rotation. The mass of the detector is centered by resilient conductive spring plates bearing on gimbal pivot shafts, which also serve as electrical connectors for the detector. Thus, two separated shaft ends journalled in one gimbal ring, which is insulated to electrically isolate the shaft ends serve as two conductors. The gimbal system is damped in a perfluorocarbon oil.
Abstract: A method is proposed for better determining the azimuth and inclination of a borehole in which a priori information regarding the magnitude of the earth's gravitational field strength, its magnetic field strength and direction are utilized to constrain the measured components of the earth's gravitational and magnetic field vectors. The constrained fit method adjusts the accelerometer and the magnetometer tri-axis measurements to optimize agreement between the measured data and the a priori magnetic and gravity field strengths and the magnetic dip angle. The adjustment that is selected is that which produces the least increase in the statistical measure .chi..sup.2.
Abstract: A pipeline survey pig including an onboard inertial reference unit and signal processing units for receiving acceleration and angular velocity signals generated by the inertial reference unit, calculating resultant values of angular velocity and accelerations and averaging the calculated values to provide recordable signals related to the position of the pig and changes in curvature of the pipe. The pig is supported by a plurality of resilient cup shaped support members which have a stiffness characteristic whereby the natural frequency of vibration which may cause lateral excursions of the pig is less than the signal generating rate yet greater than the frequency of the signal to be measured. The center of stiffness and the center of gravity of the pig are disposed along the central axis of the pig and the pipeline section being measured and are preferably coincident with each other.
Abstract: An inclination responsive device including a coil energized to produce a magnetic field extending along a normally vertical axis of the device, and a flux gate assembly adapted to respond to a horizontal component of that field upon tilting movement of the axis to an inclined non-vertical position, and to thereby produce an output which varies in response to changes in inclination. The flux gate assembly is desirably also responsive to the earth's magnetic field or another ambient field to also produce an output representing directional orientation of the device with respect to the ambient field.