Abstract: A gravity meter includes a support framework which supports a suspension system having a weight beam to which a reaction mass is attached. The reaction mass includes a dielectric mass which extends partially within first and second cavities formed between respective first and second pairs of conductors. Changes in either the ambient gravitational field or the electric potential on the conductors causes the dielectric mass to move into the first cavity between the first pair of conductors and out of the second cavity between the second pair of conductors or vice-versa, with the force on the dielectric mass being linearly proportional to the voltage between the conductors. An optical detector system determines the position of the weight beam, thus the position of the dielectric mass, and is connected to the voltage source for the plates so that, by adjusting the electric potential between the plates, the weight beam can be moved to a nulled position.

Abstract: An apparatus and method for measuring the vertical gradient of the vertical gravitational field using a gravity gradiometer comprising a housing containing a fluid, a float buoyantly supported within the fluid, mechanism for varying the metacentric height of the float, and apparatus for obtaining a measure of the gravitational gradient acting on the float resulting from varying the metacentric height.

Abstract: A tuned borehole gravity gradiometer comprises a dipole mass system having means for selectively tuning the sensitivity of the gravity gradiometer to detect variations in the earth's gravity gradient within a borehole. The tuning means includes varying the metacentric height of the dipole mass system by selectively varying the center of gravity of the dipole mass system with respect to the metacenter of the dipole mass system.

Abstract: Method and apparatus for determining the vertical gradient of the vertical gravitational field by a single measurement, for example, adjacent an earth formation of interest, are provided.

Abstract: An automated borehole gravity meter system for measuring gravity within a wellbore. The gravity meter includes leveling devices for leveling the borehole gravity meter, displacement devices for applying forces to a gravity sensing device within the gravity meter to bring the gravity sensing device to a predetermined or null position. Electronic sensing and control devices are provided for (i) activating the displacement devices, (ii) sensing the forces applied to the gravity sensing device, (iii) electronically converting the values of the forces into a representation of the gravity at the location in the wellbore, and (iv) outputting such representation. The system further includes electronic control devices with the capability of correcting the representation of gravity for tidal effects, as well as, calculating and outputting the formation bulk density and/or porosity.

Abstract: An apparatus and its use for measuring the differences in gravity at spaced locations in a wellbore. The apparatus includes first and second gravity measuring devices mounted at spaced vertical positions from each other and encapsulated for movement through a wellbore. A first electrical control current, proportional to the force of gravity acting upon the first gravity measuring device, is provided as a bias current to a second electrical control current. The second electrical control current is indicative of differences in gravity forces detected by the first and second gravity measuring devices, thereby providing a gravitational gradient reading.

Abstract: A sonic transmitter and receiver are employed to locate and evaluate zones of significant porosity in the proximity of a borehole. Continuous wave and pulse techniques are used to locate the zones and to determine the void dimensions by means of frequency domain signatures. Both through-transmission and reflection methods are employed. The technique is considered especially useful for locating fluid-filled vugular zones.

Abstract: Measurements of the gravitational field are made by generating a frequency representative of the gravitational field. In one aspect, the frequency is generated by oscillations in a magnetic vibrator formed by magnets having vertically opposed magnetic poles.

Abstract: Gravity gradiometer including a ring laser cavity, two modulator elements in the path of the laser beam, and spaced masses attached to the modulator elements to provide a differential modulation of circular polarization modes proportional to the difference in gravity at the location of the two masses. In one form, a biasing element is added to shift the operating point of the laser system to improve performance.

Abstract: Downhole variations in wireline cable tension are substantially reduced for offshore exploration by means of an auxiliary cable tensioning system preferably installed at the ocean floor wellhead. Part of the lifting force applied to a wireline cable is provided by the wireline stabilization tool at the wellhead so that fluctuations in wireline tension above the wellhead caused by ocean disturbances on the floating platform will be effectively filtered out and isolated from the main cable downhole from the wellhead. This downhole isolation is achieved with a moving wireline as well as with a stationary cable.

Abstract: A gravity gradiometer using at least one mass dipole mounted in a laser force-measurement system to detect the torque on the mass dipole generated by gravity gradient. The mass dipole is mounted on one end of a photoelastic modulator element positioned in the laser beam to differentially modulate circular polarization modes in response to application of a torque. In a preferred form, two mass dipoles are mounted on opposite ends of the modulator element which is rigidly supported at its center to improve noise rejection.

Abstract: A biasing element for use in a force-measuring system employing a circularly polarized ring laser. The biasing element is a pre-stressed photoelastic element placed in the path of the laser beam to generate a steadystate frequency difference at the output of the beat detector. In a preferred form, the biasing element is pre-stressed by bonding to a second photoelastic element and a second ring laser is positioned to detect the torque in the second element to allow monitoring of any changes in the bias level.