Abstract: Gravitational acceleration is measured in all spatial dimensions with improved sensitivity by utilizing a high temperature superconducting (HTS) gravimeter. The HTS gravimeter is comprised of a permanent magnet suspended in a spaced relationship from a high temperature superconductor, and a cantilever having a mass at its free end is connected to the permanent magnet at its fixed end. The permanent magnet and superconductor combine to form a bearing platform with extremely low frictional losses, and the rotational displacement of the mass is measured to determine gravitational acceleration. Employing a high temperature superconductor component has the significant advantage of having an operating temperature at or below 77K, whereby cooling may be accomplished with liquid nitrogen.

Abstract: The mass of stockpiled materials is determined from detailed measurements of the elevation of the pile surface at many points and the measurement of the gravitational field along several profile lines across the surface of the stockpiled material. The elevation measurements allow the calculation of the pile volume. Measured gravity values are adjusted using standard gravity corrections in such a manner as to imply all gravity data are collected along the same reference datum. Variations in the corrected gravity values are assumed to be caused solely by the pile material. The gravity measurements are interpreted using analytical and statistical methods to determine the volume-average bulk density value of the pile material. The pile volume is multiplied by the volume-average bulk density to obtain the weight of the stockpiled material.

Abstract: Apparatus to measure gravity comprising means to measure density variations in a material. Apparatus to measure gravity comprising means to measure the distribution of masses in a material. The material may be a gas comprised of one molecular species, a gaseous mixture having at least two gaseous species, liquids, or other material. Laser light is absorbed by the materials, and the re-emmitted light is measured to determine gravity in one method of measurement. Other optical processes to measure gravity are described. Other physical parameters are measured to determine gravity. Density variations measured by microwave processes and nuclear processes are also described. Apparatus are described to provide sufficiently accurate measurements of gravity to be useful for routine measurements of gravity from within a borehole in the earth to locate and quantitatively identify the amount of gas present in a hydrocarbon reservoir.

Abstract: A tool for conducting gravimetry survey downhole in an earth formation includes a pressure vessel which houses a gravity sensor that is supported by a gimbal. The gravity sensor is aligned with vertical before taking gravity measurements by a first stepper motor and a second stepper motor. The first stepper motor incrementally rotates the gimbal about the pivot axis of the gimbal while the second stepper motor incrementally rotates the gimbal about the longitudinal axis of the pressure vessel. The stepper motors are controlled by an electronic processor that responds to signals from an accelerometer assembly that measures the inclination of the pressure vessel with respect to vertical. An elevator mechanism translates the gravity sensor from one station to the next inside the pressure vessel to make gravity measurements and an optical encoder monitors the position of the gravity sensor inside the pressure vessel.

Abstract: This invention concerns improvements to gravity gradient instruments (GGI) and in particular to the accelerometers that are paired within these instruments. Accelerometers have a proof mass suspended by a spring within a magnetic field. An internal feedback loop provides a signal related to movement of the proof mass back through a reaction coil retaining the proof mass in the magnetic field, to maintain the proof mass stationary. An external feedback loop adjusts the accelerometer scale factor. The internal feedback loop provides second order compensation to the proof mass and the spring stiffness. In a further aspect the invention is a method of matching accelerometer pairs.

Abstract: A differential interferometric ballastic gravity measurement apparatus and method for measuring differential gravity between separate points employs at least two separate gravity sensors having respective free-fall masses capable of independent operation, an arrangement mounting the gravity sensors independent of one another in respective self-leveling states and at separate locations, a fiber optic-guided laser light interferometer coupled to the gravity sensors and adapted to produce a light signal indicative of a single measurement of differential gravity between the separate locations where the gravity sensors are situated, and a processing control system coupled to the gravity sensor and fiber optic-based laser light interferometer for activating independent operation of the gravity sensors and interferometer and for detecting the light signal and producing an electrical signal representing the measurement of differential gravity between the separate locations.

Abstract: Method and apparatus for conducting regional gravity surveys, comprising a gravimeter module suspended below a helicopter and adapted to be lowered to the earth's surface for generating gravimeter readings. The gravimeter module includes an automatic reading gravimeter sensor and a mechanism for self-levelling of the sensor. A ground contact sensor is provided for determining when the gravimeter module contacts the earth's surface as a result of being lowered thereto and for determining when the gravimeter module ceases contacting the earth's surface as a result of being raised therefrom. The ground contact sensor generates a time marker indicative of these events. A GPS receiver is mounted in fixed relationship with the helicopter for generating periodic position coordinates. A system is provided for receiving and recording the subsurface gravimeter readings, the periodic position coordinates, and the time marker on a common time base.

Abstract: A proof mass support system has a pair of alignment coils for controlling the rest position of an elongate proof mass. The alignment coils are constructed to provide a levitation force when they carry electric currents which varies along the length of the proof mass. The relative strength of the electric currents are tuned in the alignment coils to cause the proof mass to take up a predetermined orientation with respect to one or more degrees of freedom defined by the alignment coils. In an alternative, one or more anti-rotation coils may be arranged to apply a restoring force to the proof mass when electric currents pass therethrough. The proof mass is formed so as to cooperate with the restoring force which acts against rotation of the proof mass away from a predetermined orientation. The system is typically provided as part of a superconducting accelerometer or gravity gradiometer.

Abstract: A gravity meter has a portable housing for holding a corner cube retroreflector that can be dropped within the housing. The housing also holds a laser and an optical fiber having a first end in light communication with the laser. Additionally, the fiber has a second end which terminates at a ferrule. Light from the laser propagates through the optical fiber, and a portion of the light is reflected by the second end of the fiber back through the optical fiber to a beam splitter, while another portion of the light propagates through the second end of the fiber and is reflected by the falling corner cube back through the fiber to the beam splitter. The two reflected portions of the laser light interfere with each other to generate an interference fringe pattern which is extracted by the beam splitter.

Abstract: A proof mass support system has a pair of alignment coils for controlling the rest position of an elongate proof mass. The alignment coils are constructed to provide a levitation force when they carry electric currents which varies along the length of the proof mass. The relative strength of the electric currents are tuned in the alignment coils to cause the proof mass to take up a predetermined orientation with respect to one or more degrees of freedom defined by the alignment coils. In an alternative, one or more anti-rotation coils may be arranged to apply a restoring force to the proof mass when electric currents pass therethrough. The proof mass is formed so as to cooperate with the restoring force which acts against rotation of the proof mass away from a predetermined orientation. The system is typically provided as part of a superconducing accelerometer or gravity gradiometer.

Abstract: A device is proposed to detect the existence of a hypothetical Universal Particle Field of the Universe. According to this hypothesis, this energy field is responsible for all gravitational, and inertial phenomena in the Universe. The proposed device is quite simple, and it is quite practical to build. This device may also settle the controversy between the advocates of the hypothetical "Field Generated By Matter" vs. the "Universal Particle Field" advocates. The device consists of a rotor, surrounded by a relatively large Universal Particle shading mass. A mass free slot, in line with a segment of the rotor rim mass, allows slightly less attenuated Universal Particle beams, than 180 degrees from this slot, to impinge on the rotor rim segment mass. Calculations given, indicate that a 10 kg rotor rim segment mass, with a 100,000 kg removed mass from the slot, results in a force on the rotor rim of about 6.67.times.10.sup.-5 Newtons.

Abstract: A flexural pivot bearing includes a pair of members with opposed close-spaced faces which are joined by a web (29), of microscopic thickness, in a plane intersecting the faces. These members and the web are comprised of an integral body (27) of substantially uniform material, and the members are adapted for pivoted mutual flexure about a pivot axis aligned along the web.

Abstract: A gravity meter has a portable housing for holding a corner cube retroreflector that can be dropped within the housing. The housing also holds a laser and an optical fiber having a first end in light communication with the laser. Additionally, the fiber has a second end which terminates at a ferrule. Light from the laser propagates through the optical fiber, and a portion of the light is reflected by the second end of the fiber back through the optical fiber to a beam splitter, while another portion of the light propagates through the second end of the fiber and is reflected by the falling corner cube back through the fiber to the beam splitter. The two reflected portions of the laser light interfere with each other to generate an interference fringe pattern which is extracted by the beam splitter.

Abstract: A method for producing isostatically corrected gravity displays using available gravity data sets. The values of crustal density, density contrast between lower crust and mantle, and crustal thickness at sea level required for the Airy-Heiskanen equation are determined by analysis of the data set. Crustal density is determined by fractal analysis. Density contrast is determined by cross plotting Bouguer anomaly values versus elevation. Crustal thickness is determined by plotting power spectra of free-air gravity grids. The values are then used in the Airy-Heiskanen equation to provide the value of depth to crust-mantle boundary at each data point location in order to make accurate isostatic corrections and to produce accurate isostatically corrected displays.

Abstract: An improved technique more accurately determines pore pressure of sedimentary rock penetrated by a borehole from the earth's surface. Formation overburden is directly measured at one or more locations in the borehole, and a log of formation overburden is generated using the measured overburden pressures and conventional geophysical data. A linear relationship has been determined between the logarithm of effective stress for a specific mineral and the logarithm of solidity, which allows the maximum effective stress and the compaction exponent for that mineral to be determined. This linear relationship enables the effective stress and compaction exponent for rock comprising a combination of minerals to be precisely determined at multiple borehole intervals. The effective stress and overburden calculated according to the techniques to the present invention are particularly useful to geologist and well planners in the oil and gas industry.

Abstract: A method of geophysical exploration is provided whereby satellite derived and surface acquired gravity data sets can be employed to produce a merged gravity data set. In particular, surface acquired gravity data can be filtered so as to have a frequency content matching the satellite acquired gravity data. Employing mistie analysis, both gravity data sets can be combined to produce a merged gravity data set. The resulting merged gravity data set provides means for referencing both non-overlapping surface acquired gravity data sets and satellite derived gravity data sets to a common or reference datum such that they can be compared directly.

Abstract: Conventional surface gravity measurements, either land, sea, or sea bottom, are made along a line that lies approximately along the same surface orientation as the deviated well. Borehole gravity measurements are made in the deviated part of the well along the wellbore at stations lying approximately below those taken on the surface. The gravity difference is computed from the station pairs. From the gravity difference and the vertical distance between the two readings, the average density is computed for all the station pairs. From a depth model interval depths at each layer between the surface and the borehole stations are computed. The average density between any station pairs can be related to the interval densities and the layer densities are calculated.

Abstract: Shipboard gravity data are currently recorded with one shipboard gravity meter. Gravity data are tied to the international gravity datum when the boat docks about every 30 days. The accuracy of these data is about 0.5 milligals and not sufficiently accurate for detailed quantitative interpretation. It is possible to increase the accuracy of shipboard gravity data twofold by using the procedure we have described. A stable boat with precision navigation and water depth soundings is necessary. Two gravity meters are calibrated to read the same values and times. These are placed near the center of the boat with one meter facing forward and one facing backward for plus and minus cross coupling, or simultaneous accelerations in different directions. Integration of the gravity recordings cancels random noise. This innovation increases the accuracy to 0.35 milligals. Shipboard gravity data are tied to a coarser grid of still gravity readings tied to the international gravity datum at land locations.

Abstract: Superconducting bearings inhibit the excitation of modes in a superconducting force measuring instrument such as a superconducting gravimeter, and effecively damp such modes in the event they are excited. Excitation of modes is inhibited by magnetically and/or physically blocking orbital and rotational motions. Modes which are excited are efficiently damped, preferably by inducing eddy currents in lossy metal parts. These dissipative eddy currents remove energy from the motion, causing the motion to decay exponentially with time. A significant advantage of the bearing design is that the magnetic field of the bearing can be isolated from the main levitation system. This ensures that the bearing interferes minimally with the gravity measurement.

Abstract: A method is disclosed for determining a component of the response of a reservoir to tidal forces (such as the amplitude of variation or delay time) in a hydrocarbons reservoir. That method comprises measuring a variable responsive to tidal forces within the reservoir over a measurement time period, determining a theoretical earth-tide for the reservoir over that measurement time period, and determining the component of the response to tidal forces by comparing the variable measurements and the theoretical earth-tide determinations. Examples of variables that are responsive to the tidal forces are fluid level in a borehole, pressure, and borehole stress. The measurement time period should be sufficiently long so that both a maximum and minimum variable measurement is achieved during that time period (e.g., fourteen or twenty-four hours).

Abstract: For the measurement of accelerations, e.g. gravitation components for goniometry, in the oscillating circuit of two RC oscillators capacitors are provided, which in a common, metallic casing between two electrode plates (2,3) have a spring-elastically held, common, circular deflection part. In order to avoid dielectric interference, the electronic means are arranged on one side of the instrument, are surrounded by a metallic cover and their electrical connection to the more remote electrode plate takes place by a wire, which is passed in contact-free manner through a central hole in the circular deflection part and the closer electrode plate. The spacing between the deflection part and the electrode plates remains constant in the case of a non-deflected deflection part, in that its size forms a ratio .sub.E - .sub.M : .sub.M to the thickness of the spacers insulating the electrode plates from the metallic casing, .sub.E corresponding to the thermal expansion coefficient of the spacers and .sub.

Abstract: Apparatus and method for establishing a level plane and with respect to the level plane, vertically aligning an acceleration sensitive axis of a gravity measurement device (10). The gravity measurement device includes an accelerometer (68), which is rotatably mounted on a gimbal shaft (62) within a gimbal frame (54). The gimbal frame is also rotatable about a longitudinal axis that is preferably oriented at a right angle to the longitudinal axis of the gimbal shaft. A stepping motor (20) is connected through an antibacklash gear (30), an idler gear (32) and an antibacklash gear (48) to a drive shaft (50). Rotation of this drive shaft causes the accelerometer to rotate about the gimbal shaft. In a similar fashion, a stepping motor (22) is drivingly connected to a drive shaft (56), used to rotate the gimbal frame.

Abstract: Each accelerometer includes a cylindrical proof mass made of a superconducting material. Each proof mass includes annular upper and lower hollowed out portions longitudinally surrounded by a cylindrical exterior wall. Common mode and differential mode sensing coils are arranged adjacent a bottom-side surface of the proof mass in one hollowed out annular portion and a levitation coil is arranged adjacent a bottom-side surface of the proof mass in the other hollowed out annular portion. The common mode, differential mode and levitation coils are connected in respective first, second and third superconducting circuits. The first circuit produces common mode signals indicative of forces acting on both accelThis invention was made with government support under Contract No. NAS 8-36165 awarded by the National Aeroanutics and Space Administration. The government has certain rights in this invention.

Abstract: A device for acceleration measurements and, in particular, for gravitational field measurements in, for example, earth orbits, which has a body arranged movably in a force field, the position of which can be detected by a position location device. The force acting upon the body is anisotropic and, at least in the direction of the acceleration to be determined, is not a linear function of the deflection of the body from its resting position. In a preferred further development the body is suspended by four tension springs, which in the resting position of the body are arranged in a plane perpendicular to the direction of the acceleration to be determined, and which each form right angles with the adjacent spring. With 3 separate optoelectronic position detector receivers plus corresponding illuminators which provides some measurement redundancy, all acceleration planes can be measured with a great dynamic range. In the main direction, forces as small as 10.sup.-12 g will be measurable.

Abstract: A gravity gradient logging tool is used to conduct a gravimetry survey of an earth formation. A pair of piezoelectric transducers are located at spaced apart positions within the logging tool. Each transducer is loaded with a known mass and excited electrically so as to vibrate at a characteristic resonant frequency. The period of vibration of each transducer is measured as the logging tool continuously traverses the formation. The difference in the measured periods of vibration is determined as a measure of gravity gradient along the formation.

Abstract: An affinity type gravity measurement instrument which is composed of material such as wood having a coefficient of thermal expansion. Within an internal cavity defined within the housing is disposed a quantity of liquid and a float partially submerged in the liquid. The liquid and float have low coefficients of thermal expansion. The housing defines an internal temperature compensation cavity receiving liquid upon expansion thereof to thus minimize change in the height of the liquid column and thus change in the position of the float and target response to temperature change. A stem of the float extends through an opening at the upper portion of the housing and supports a target, the position of which is sensed by an eddy current, laser or radar proximity sensor, developing signals which are processed for digital readout and computer processed for mapping.

Abstract: A digitizer for a gravity meter having a rotatable gradient readout dial and a null indicator, the digitizer comprising a shaft position sensor attached to the readout dial for providing a digital output signal representation of clockwise and counterclockwise rotation of the readout dial during nulling of said indicator, a microprocessor coupled to the shaft position sensor for receiving and storing the sensor digital output signal representation and means in the microprocessor for analyzing the stored digital output signals from the shaft position sensor and producing and storing a digitized output signal representing the gravity in the form of the average position of the readout dial on the gravity meter.

Abstract: A method and apparatus for measuring acceleration and/or gravity are disclosed. At least one auxiliary mass is provided which, in cooperation with apparatus in accordance with the invention, is alternately engaged to and disengaged from the proofmass of an accelerometer to provide two distinct torque values, each value including a pendulosity-modulated component and an unmodulated component from which a value of acceleration and/or gravity may be extracted that is essentially free from bias uncertainty.

Abstract: An improved method that directly and continuously determines the magnitude f the earth's gravity in relation to a user platform at one or more selected points on or above the earth's surface. An improved Global Positioning System (GPS) is used to carry out the method and is made up of a plurality of twenty-four (24) continuously orbiting GPS satellites that are arranged into three groups of eight satellites with each group or constellation being disposed in its respective plane of a series of three longitudinal planes. Each plane is arranged in predetermined angular and spatial relation to the earth's equatorial plane and the other planes of the series. Any GPS satellite continuously transmits a pair of encoded RF signals at predetermined L-band frequencies. By virtue of this global arrangement of the 24 satellites, the antenna field of view of a user platform is capable of receiving at any time the encoded signals of at least six satellites.

Abstract: In a gravimeter the measuring mass is supported by springs which are arranged in regular array around the measuring mass and exert pressing forces on the measuring mass along lines of action extending at an angle to the horizontal. The state of equilibrium with a predetermined value of the acceleration due to gravity coincides with an extreme value of the force-versus-deviation characteristic of the spring system, whereby the measuring mass is held practically free from restoring forces by the spring system. A sensor detects deviations from a zero position and controls a restoring force generator. Two counter-acting sets of springs are provided. The springs are tension springs, the tensional force of which acts on the measuring mass as a pressing force through a lever transmission. A measuring range spring permits setting of measuring ranges. An advantageous construction therefor is described.

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: Method and apparatus are disclosed for airborne gravity surveying in which the airborne vehicle is stabilized with respect to speed, direction of heading and altitude, and in which the gravity meter has adequate sensitivity and signals that are recorded at a high sample rate on a magnetic tape, in which the aircraft position is computed using a multi-range navigation system that is located geodetically.

Abstract: A gravity meter is provided which has a support framework which supports a suspension system having a weight arm to which a reaction mass is attached. The reaction mass includes a dielectric mass which extends partially into a cavity between a pair of conductors. Changes in either the ambient gravitational field or the electric potential on the conductors causes the dielectric mass to be moved into or out of the cavity between the conductors allowing both fine tune calibration of the device by means of varying the electric potential and direct readout of the device by measuring the electric potential required to equilibrate the conductor and dielectric system. The suspension assembly includes a pair of parallel spindles rotatably mounted on hinges secured to the support framework with the spindles being interconnected by a zero length mainspring and temperature compensating framework.

Abstract: A method for borehole gravimetric determination of residual oil saturation of a formation is described. In a preferred embodiment plural measurements of the local gravity are taken at each of spaced locations within a well and those departing more than a statistically determined distance from the mean of the measurements taken at a given location are deemed to be in error and are not used in calculation of the density of the formation at a given point.

Abstract: A subsurface formation surrounding a borehole is flushed with at least one fluid having a density difference from that of the water content of the formation. Borehole gravity logs are recorded. Porosity is also recorded. From the density, gravity and porosity indications, water and oil saturation of the formation is determined.

Abstract: A gravity meter is formed by securing two parallel rods of different material at adjacent ends and indicating their differential elongation at the free ends. While capacitor, interferometer, and other devices could be used to measure this differential, the presently preferred indicator is a roller disposed between the free ends and the rotation due to differential elongation is indicated optically by a mirror attached to the roller. The indicator is zeroed while the rods are horizontal and the difference in elongation of the two rods is indicated when the rods are moved to a vertical position. The device may be moved over the earth's surface in the vertical position, while held at a constant temperature, to become a gravity meter.

Abstract: A highly compact and portable free-fall apparatus for the absolute determination of the acceleration of gravity, which allows for rapid, convenient and precise measurements. The apparatus utilizes mercury as the falling mass and has design features that makes it possible to carry out experiments in vacuum or various gaseous environments under controllable conditions of temperature and pressure. The apparatus conveniently and automatically generates a large number of data in a relatively short period of time allowing for meaningful statistical analysis.

Abstract: A rotor mounting a sensor to be inserted into the earth is rotatably mounted within and locked to a cylindrical housing. The latter may be dropped to the earth and may come to rest in any orientation. When at rest, the rotor is unlocked and a drive mechanism rotates the rotor with respect to the housing. Gravity causes a ball in a tortuous path in the rotor to traverse the path and to drop into one of a plurality of annularly spaced recesses in the housing when the rotor reaches a desired orientation. With the ball in place in a recess, a wedge surface on the rotor wedges against a portion of the ball extending from the recess and this stops the rotor--in the desired orientation.

Abstract: Gravity measuring apparatus is disclosed. In the preferred and illustrated embodiment, an apparatus utilizing a balanced container floating in a liquid rises and falls according to variations in gravity. Such variations in position are coupled to a measuring apparatus. In one embodiment, a horizontal beam pivotally mounted at one end and connected to the float as its center and nearly balanced about the pivot support at one end is deflected as the float rises and falls. Movement thereof is connected to a multiplier which enlarges the movement by some scale factor convenient to the circumstances in the range of 100 to about 1,000 to form an enlarged deflection of the multiplier adjacent to a motorized recorder, thereby forming a usable output indicia.

Abstract: For use in a gravity meter, an improved gravity sensor is disclosed which, in the preferred and illustrated embodiment, balances on an axis of rotation which is perpendicular to the vertical component of gravity, thereby enabling the arm on the apparatus to respond to horizontally resolved components of gravity.

Abstract: A portable accelerometer unit is described for measuring deviations or excursions from a datum due to an applied load or force. The portable accelerometer unit includes an accelerometer device mounted by suspension means in a housing, and is operable to generate an output signal in response to the applied load. An electrical circuit is also provided connectible to the accelerometer device to receive the output signal therefrom. This circuit includes at least one operational amplifier stage containing an operational amplifier. This amplifier has two input terminals and an output terminal. One of the input terminals is connected through a first variable resistance to a power supply. The other input terminal is connected to the accelerometer to receive the output signal therefrom. This other input terminal also has a feedback circuit operatively connected to it. The feedback circuit is controlled by a second variable resistance, whereby to effect zeroing of an accelerometer output signal due to gravity.

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.

Abstract: To locate potentially hydrocarbon-bearing subsurface formations, tiltmeters measure the time of arrival and the apparent direction of a lunar-induced earth tide at an array of points on the earth's surface. The measurements are combined to determine the shape of the tidal wave in a region of interest. The shape is indicative of subsurface viscosity in the region. Subsurface formations having an abnormally low viscosity are considered potentially hydrocarbon bearing.

Abstract: A device for measuring accelerations, particularly components of accelerations due to gravity comprises a stator having first and second spaced apart electrodes. A deflecting part is suspended between the first and second electrodes and it is displaceable under the influence of gravity in a direction toward one or the other electrodes and in so doing produces an electric signal which is proportional to the displacement amount. The signal is connected to means for indicating the magnitude of displacement as a measure of the acceleration acting upon the device.

Abstract: The invention disclosed herein is comprised of an electric generator powered by an electric motor that is activated by any source of electricity so that the torque of the electric motor reacting against its stator assembly and the action of the stator of the generator resisting the magnetic force of its rotor both act to electrically indicate the differences in acceleration of gravity and other accelerations when electrically-measured by electric current-measuring means.