Abstract: In a method for determining the presence of gas in a region of investigation of earth formations surrounding a borehole. A movable logging device is used to generate two sequences of magnetic field pulses having different pulse spacing times. Each of the pulse sequences elicits a corresponding sequence of nuclear magnetic resonance spin echoes. The presence of gas in the formation, is determined from ratios of signals derived from the two spin echoes sequences.

Abstract: The instruments of a pulsed nuclear magnetic resonance device are included in a drill collar for evaluating earth formations. The resulting tool makes NMR measurements through an electrically non-conductive shield while the formation is being drilled.

Abstract: Apparatus and method are disclosed for determining a nuclear magnetic resonance property of formations surrounding a borehole while drilling the borehole with a rotating drill bit on a drill string.

Abstract: A logging-while-drilling tool contains a pulsed nuclear magnetic resonance (NMR) device for evaluating earth formations. An antenna of the pulsed NMR device is electromagnetically coupled with a drill collar of the tool for evaluating earth formations. In this way, the antenna generates a magnetic dipole parallel to a surface of the drill collar and the drill collar enhances the electromagnetic field generated by the antenna.

Abstract: A permanent magnet of a pulsed nuclear magnetic resonance (NMR) device is positioned within a drill collar for evaluating earth formations. In this way, the torsional and bending strengths of the drill collar are maximized with relatively little sacrifice of the magnetic moment of the permanent magnet. The resulting tool makes NMR measurements while the formation is being drilled. An antenna for producing and detecting an oscillating RF field in the earth formation is either located in a groove in the outer surface of the drill collar, or in an alternative embodiment, the drill collar itself serves as an RF antenna.

Abstract: A method is disclosed for determining a nuclear magnetic resonance characteristic and the resistivity of earth formations surrounding a borehole, including the following steps: passing a logging device through the borehole; producing, at the logging device, a static magnetic field; producing, at the logging device, electromagnetic energy having a field component in the formations that is orthogonal to the static magnetic field; receiving, at the logging device, electromagnetic energy that has passed through said formations; and determining, from the received electromagnetic energy, the nuclear magnetic resonance characteristic of the formations and the resistivity of the formations.

Abstract: A nuclear magnetic resonance (NMR) logging technique reveals the volume of hydrocarbons in an earth formation. The differences in viscosity among gas, oil and water are used to distinguish among these three fluids. During NMR logging, a parameter of a sequence of magnetic field pulses is altered, causing echo signal strengths to vary due to the diffusion of the fluids in the formation. The volume of hydrocarbons in the formation is determined from detected spin echo strengths. The invention applies to wireline NMR logging and NMR logging-while-drilling techniques.

Abstract: The instruments of a pulsed nuclear magnetic resonance device are included in a drill collar for evaluating earth formations. The resulting tool makes NMR measurements through an electrically non-conductive shield while the formation is being drilled.

Abstract: The instruments of a pulsed nuclear magnetic resonance (NMR) device are included in a drill collar for evaluating earth formations. The resulting tool makes NMR measurements while the formation is being drilled. Permanent magnets produce a static field in the earth formation. Shimming permanent magnets inside or outside the drill collar suppress the magnetic resonance of borehole fluids. The permanent magnets are manufactured from two magnetic materials, for example.

Abstract: A permanent magnet of a pulsed nuclear magnetic resonance (NMR) device is positioned within a drill collar for evaluating earth formations. In this way, the torsional and bending strengths of the drill collar are maximized with relatively little sacrifice of the magnetic moment of the permanent magnet. The resulting tool makes NMR measurements while the formation is being drilled. An antenna for producing and detecting an oscillating RF field in the earth formation is either located in a groove in the outer surface of the drill collar, or in an alternative embodiment, the drill collar itself serves as an RF antenna.

Abstract: A borehole logging tool comprises a Nuclear Magnetic Resonance (NMR) tool and is pulsed according to a selected Carr Purcell-Meiboom Gill (CPMG) sequence. Because the recovery time between CPMG sequences is short, the sequence acts as a filter such that signals induced by rapidly relaxing nuclei of fluid bound in an earth formation are detected. In this manner, the NMR tool gives a direct indication bound fluid volume and fast logging speeds are achieved.

Abstract: The instruments of a pulsed nuclear magnetic resonance (NMR) device are included in a drill collar for evaluating earth formations. The resulting tool makes NMR measurements while the formation is being drilled.

Abstract: A method of determining the resistivity of an underground formation surrounding a cased borehole including the steps of: a) passing a current along a first pan of the casing and measuring the voltage; b) passing a current along a second part of the casing and measuring the voltage, the second part being spaced from the first part by an intermediate region; c) measuring voltages between the first part of the casing and a point in the intermediate region and between the second part of the casing and the same point; and d) using the measured voltages to derive the resistivity of the formation.

Abstract: The disclosure invention is directed to a nuclear magnetic resonance measurement apparatus that can be utilized in a logging device which operates generally centrally in a borehole, and has a generally circumferential region of investigation, but which permits usage of relatively powerful permanent magnets, such as rare-earth magnets, that are not permeable to the RF magnetic field. This is achieved by employing side-by-side spaced apart elongated magnets, and an RF current loop in the region between the magnets. In a disclosed embodiment, the magnets are each in the shape of a segment of a cylinder, and the respective axes of elongation of the magnets are parallel. The magnets have respective casings with electrically conductive surfaces, and the RF current loop includes at least a portion of the conductive surfaces of the magnet casings.

Abstract: An NMR pulse sequence for use in a borehole logging tool includes a series of CPMG pulses according to:T.sub.r -90.degree..sub..+-.x -(t.sub.cp -180.degree..sub.y -t.sub.cp -echo.sub.j)where j is the index of CPMG echoes gathered, T.sub.r is wait time, t.sub.cp is the Carr-Purcell spacing. This pulse sequence is used to determine Bound Fluid Volume (BFV) which is subtracted from total porosity to yield Unbound Fluid Volume (UFV) of a formation surrounding the borehole. Measuring the BVF, the amount of rapidly relaxing fluid (less than 50 ms), is more efficient than measuring UFV (up to 2 secs), and is insensitive to motion of the logging tool.

Abstract: The disclosure invention is directed to a nuclear magnetic resonance measurement apparatus that can be utilized in a logging device which operates generally centrally in a borehole, and has a generally circumferential region of investigation, but which permits usage of relatively powerful permanent magnets, such as rare-earth magnets, that are not permeable to the RF magnetic field. This is achieved by employing side-by-side spaced apart elongated magnets, and an RF current loop in the region between the magnets. In a disclosed embodiment, the magnets are each in the shape of a segment of a cylinder, and the respective axes of elongation of the magnets are parallel. The magnets have respective casings with electrically conductive surfaces, and the RF current loop includes at least a portion of the conductive surfaces of the magnet casings.

Abstract: A borehole logging tool comprises a Nuclear Magnetic Resonance (NMR) tool and is pulsed according to a selected sequence. An interpretation is performed which involves a singular value decomposition and compression of data obtained by the tool. The compressed data is then subjected to a nonegative, linear least square fit to obtain a distribution function. The distribution function is used in determining bound fluid volume, unbound fluid volume, total porosity, spin-lattice relaxation time, spin-spin relaxation time, and mean relaxation time using only the pulse NMR tool.

Abstract: An apparatus is disclosed for investigating nuclear magnetic resonance properties of earth formations traversed by a borehole, including a logging device adapted for longitudinal movement in the borehole. The device includes a first subsystem for producing a static magnetic field in the formations and a second subsystem for transmitting electromagnetic energy into the formations and for detecting electromagnetic energy from the formations. The second subsystem comprises an antenna assembly which includes an open-ended shell formed of a magnetically permeable material. An open-ended electrically conductive body is disposed within the shell and is spaced therefrom. A medium whose acoustic impedance is substantially different than the acoustic impedance of the shell and the body is disposed between the shell and the body. An electrically conductive probe is disposed in the body, and an electrically insulating magnetically permeable loading material disposed in the body.

Abstract: Borehole NMR logging apparatus and methods, and methods for the interpretation thereof. A logging tool is provided which produces a strong, static and homogeneous magnetic field B.sub.0 in a Volume of an adjacent formation on one side of the tool to measure nuclear magnetic resonance characteristics thereof. In the preferred embodiment, the tool has an RF antenna mounted on the outside of the metal body of the tool, directing focussed oscillating magnetic fields B.sub.1 at said Volume to polarize or tip the Magnetic moments of hydrogen nuclei of fluids within rock pores. The same antenna can be used to receive signals of proton precession in the Volume of interest immediately after transmission of the RF polarizing field B.sub.1. Extremely rapid damping of the antenna between the transmitting and receiving modes of operation is accomplished by a Q-switch disclosed herein. The invention provides for the direct measurement of NMR decay having transverse relaxation time T.sub.

Abstract: Borehole NMR logging apparatus and methods, and methods for the interpretation thereof. A logging tool is provided which produces a strong, static and homogeneous magnetic field B.sub.0 in a Volume of an adjacent formation on one side of the tool to measure nuclear magnetic resonance characteristics thereof. In the preferred embodiment, the tool has an RF antenna mounted on the outside of the metal body of the tool, directing focussed oscillating magnetic fields B.sub.1 at said Volume to polarize or tip the magnetic moments of hydrogen nuclei of fluids within rock pores. The same antenna can be used to receive signals of proton precession in the Volume of interest immediately after transmission of the RF polarizing field B.sub.1. Extremely rapid damping of the antenna between the transmitting and receiving modes of operation is accomplished by a Q-switch disclosed herein. The invention provides for the direct measurement of NMR decay having transverse relaxation time T.sub.