Abstract: A method and apparatus are disclosed for using nuclear magnetic resonance (NMR) techniques to obtain information relating to fluids present near geologic structures. A modular NMR tester which can be located within a standard modular logging tool is used for direct downhole NMR measurements of various parameters of fluid samples of geologic formations near the walls of a borehole. The tester has a vessel made of a non-conductive material and a surrounding permanent magnet that creates a uniform static magnetic field within the test chamber of the vessel. An RF coil is embedded in the walls of the vessel and is used to induce excitation field with a direction perpendicular to the static magnetic field. Fluids located proximate the borehole are introduced into a test chamber of the tester. NMR signals from the excited nuclei in the fluids are detected to obtain data for calculating a number of important fluid parameters and for the interpretation of wireline MRIL measurements.

Abstract: A method and apparatus for processing nuclear magnetic resonance (NMR) information to differentiate between oil based mud filtrate (OBM), and connate oils, during subsurface exploration. An NMR experiment is performed on a sample of formation fluid, and the resulting data is then processed to differentiate between the relaxation time parameters characteristic of OBMs and those characteristic of connate oils. A simple arithmetic difference between relaxation times calculated for successive samples may be followed by a distributional analysis performed in either the time domain or relaxation spectrum domain. The process is repeated for other fluid samples and the data for successive fluid samples is compared so that the user may determine when the formation fluid consists almost entirely of connate oil.

Abstract: A logging while drilling (LWD) and measuring while drilling (MWD) method and device are disclosed for reducing the sensitivity of NMR measurements to tool motions. The invention is based on NMR relaxation measurements determining longitudinal relaxation times T1 instead of the standard T2 measurements, and involves saturating a relatively wide sensitive region of the formation and processing NMR echo signals which originate approximately from the center of the sensitive region.

Abstract: A method and apparatus are described using nuclear magnetic resonance (NMR) measurements for obtaining information relating to properties of geologic structures in highly conductive borehole environments. A centralized NMR logging probe is provided with a sleeve having a semi-circular RF shield that blocks signals from one side of the probe and with elements that press the uncovered side of the probe to the sidewall of the borehole. In highly conductive boreholes, the eccentrically-positioned modified probe results in increased signal-to-noise ratios and savings in peak power and energy compared with the use of standard centralized tools. The modified probe further suppresses unwanted NMR signals.

Abstract: An NMR pulse sequence and signal processing method is disclosed for measurement of fast decay response signals from materials containing a fluid state. The proposed pulse sequence and processing method are applicable in borehole NMR logging as well as measurements of attributes of man-made or natural materials. The disclosed pulse sequence comprises a series of short NMR pulse trains separated by intervals which are shorter than the time required for polarization of nuclear magnetization in bulk fluids of the fluid state. By stacking response signals to increase the signal to noise ratio, time domain data is obtained that generally corresponds to transverse decay components as short as about 0.5 ms. Various attributes of the materials being investigated can be derived in a single measurement.

Abstract: A well logging system and method for detecting the presence and estimating the quantity of gaseous and liquid hydrocarbons in the near wellbore zone. The system uses a gradient-based, multiple-frequency NMR logging tool to extract signal components characteristic for each type of hydrocarbons. To this end, a new data acquisition method is proposed in which measurements at different frequencies are interleaved to obtain, in a single logging pass, multiple data streams corresponding to different recovery times and/or diffusivity for the same spot in the formation. The resultant data streams are processed to determine mineralogy-independent water and hydrocarbon saturations and porosity estimates. Gas and oil saturations are used to obtain accurate estimates of the water content, permeability and other parameters of interest.

Abstract: A simple, pore-level model for diffusion and NMR relaxation of oil-water mixtures in water wet pores has been developed. In addition to lending physical insight into the relaxation time behavior of mixed pore fluids, the model can be used to generate a practical tool for interpreting diffusion log data, i.e., a T2 vs. D cross plot. Locating points on the cross plot simultaneously yields the near wellbore water saturation and the rock pore size. For light oils, T2 is shown to be mainly a pore size indicator whereas D is controlled mainly by Sw. The pore size "resolution" decreases as oil viscosity and/or Sw decreases. A preliminary verification of the model has been made with limited core data and the results of applying the model to interpreting NMR log data are encouraging.

Abstract: An improved system for using magnetic resonance techniques to obtain information relating to geologic structures is disclosed. The system of the present invention uses values of the total porosity of a formation and the porosity obtained via NMR pulse echo techniques to derive additional information relating to the underlying geologic structures, including resistivity and water saturation. Independent estimate is provided to account for the presence of clay mineral content.

Abstract: A method and apparatus is disclosed for efficient processing of nuclear magnetic resonance (NMR) echo trains in well logging. Apriori information about the nature of the expected signals is used to obtain an approximation of the signal using a set of pre-selected basis functions. A singular value decomposition (SVD) is applied to a matrix incorporating information about the basis functions, and is stored off-line in a memory. During the actual measurement, the apparatus estimates a parameter related to the SNR of the received NMR echo trains and uses it to determine a signal approximation model in conjunction with the SVD of the basis function matrix. This approximation is used to determine in real time attributes of the earth formation being investigated.

Abstract: An improved system for using magnetic resonance techniques to obtain information relating to geologic structures. The system of the present invention uses values of bulk-volume irreducible water and porosity obtained via the magnetic resonance techniques to obtain additional information relating to geologic structures, including water saturation.

Abstract: An improved system for using nuclear magnetic resonance techniques to obtain information relating to geologic structures. The system of the present invention employs a variable sampling window which increases sampling efficiency by allowing the system to optimize the sampling interval, thereby maximizing the amount of data which can be obtained in a series of data samples.

Abstract: Nuclear magnetic resonance well logging apparatus and a method of use for geophysical examination of a bore hole as the bore hole is drilled. The apparatus is connected to the drill bit to follow it through the bore hole as the bore hole is formed. The apparatus comprises a resilient, tubular, permanent magnet for generating a static magnetic field in the region of a portion of the bore hole adjacent the apparatus, which region includes materials sought to be analyzed, an antenna mounted on the magnet and connected to associated circuitry for exciting nuclei of the materials sought to be analyzed in the region, and a receiver connected to the antenna for receiving nuclear magnetic resonance signals from the excited nuclei and for providing an output signal indicative of properties of the materials sought to be analyzed.

Abstract: A method for conducting borehole NMR measurements comprising the steps of:providing a magnetic field and a magnetic field gradient at a desired location along a borehole;carrying out at least one NMR experiment in the presence of the magnetic field gradient;sensing the diffusion effect on the decay of at least the first echo; anddetermining therefrom the diffusion coefficient.Apparatus for carrying out the method is also described.

Abstract: A magnetic structure for producing a substantially uniform magnetic field in a region external to the structure. The field produced has a predetermined magnitude but with all of its first and second order partial derivatives with respect to spatial coordinates being equal to zero at any selected point within the uniform region. The structure includes a pair of elongated magnets which are magnetized along their longitudinal axis. The magnets are spaced from each other with their corresponding end poles facing each other. A pair of annular cylindrical magnets which are magnetized in a radial direction are mounted on the end faces of each of the elongated magnets. Another annular cylindrical magnet, also having its magnetization oriented in a radial direction is located on the midplane between the two elongated magnets. The combined effect of these magnets is to create a uniform toroidal field. This field is particularly suitable for use in NMR oil well logging applications.

Abstract: Nuclear magnetic resonance sensing apparatus including at least three magnets operative to generate a static magnetic field in a region remote therefrom containing materials sought to be analyzed, the at least three non-conductive permanent magnets being arranged along a longitudinal axis in side to side arrangement and having generally uniform cross sections, which, when joined, together define a circular cross section, the overall length of said at least three magnets along said longitudinal axis being greater than their dimensions perpendicular to said longitudinal axis and greater than twice the radial separation of said remote region and said longitudinal axis, the at least three magnets being magnetized in magnetization directions extending generally perpendicular to the longitudinal axis, at least one of the at least three magnets having a magnetization direction opposite to the magnetization direction of at least another one of the at least three magnets, the static magnetic field having a static fiel

Abstract: Nuclear magnetic resonance sensing apparatus includingone or more magnets operative to generate a static magnetic field in a region remote therefrom containing materials sought to be analyzed, the one or more magnets defining a longitudinal axis, the static magnetic field having a static field direction substantially perpendicular to the longitudinal axis and having generally uniform amplitude along the azimuth with respect to the longitudinal axis in the remote region;apparatus for generating a variable magnetic field in said remote region in a direction substantially parallel to the static magnetic field;apparatus for generating a radio frequency magnetic field in the remote region for exciting nuclei of the materials sought to e analyzed and having a radio frequency magnetic field direction substantially perpendicular to both the longitudinal axis and to the static field direction; andapparatus for receiving nuclear magnetic resonance signals from the excited nuclei and for providing an output indication o

Abstract: Nuclear magnetic resonance sensing apparatus including one or more magnets operative to generate a static magnetic field in a region remote therefrom containing materials sought to be analyzed, the one or more magnets defining a longitudinal axis, the static magnetic field having a static field direction substantially perpendicular to the longitudinal axis and having generally uniform amplitude along the azimuth with respect to the longitudinal axis in the remote region;apparatus for generating a radio frequency magnetic field in the remote region for exciting nuclei of the material sought to be analyzed and having a radio frequency magnetic field direction substantially perpendicular to both the longitudinal axis and to the static field direction; andapparatus for receiving nuclear magnetic resonance signals from the excited nuclei and for providing an output indication of the properties of the material sought to be analyzed.Methods for nuclear magnetic resonance sensing are also described and claimed.