Abstract: A method of cancelling ghosts from NMR images. The method involves estimating a phase difference function .DELTA. (n.sub.1, n.sub.2) and using that function to solve a linear system of equations to find the magnitudes of the true object densities at the true image and ghost locations x(n.sub.1,n.sub.2) and x(n.sub.1,n.sub.2 +N/2), respectively, where the image has dimensions N.times.N.sub.s. Experimental values of .DELTA. (n.sub.1, n.sub.2) for a variety of objects indicate that its variation along n.sub.1 is considerably larger than along n.sub.2. Thus, for each column n.sub.1, the phase difference function .DELTA. (n.sub.1, n.sub.2) can be modelled as a one-dimensional function of n.sub.2 with two parameters .alpha. (n.sub.1) and .beta. (n.sub.1), which are estimated from the pixels in the 2-D FFT processed reconstructed image Y(n.sub.1,n.sub.2). These parameters are then used to estimate .DELTA. (n.sub.1, n.sub.2), which is ultimately used to de-ghost the image.

Abstract: An MRI method and device for fast determination of the transverse relaxation time constant T2 utilizes the fact that this time constant introduces asymmetry into all magnetic resonance echo signals (::exp(-t/T2) enabling determination of the time constant T2 from the asymmetry of the echo signals. During the determination of a spin density distribution the value of the time constant T2 can be determined for each pixel. After Fourier transformation of the resonance signal, integration of the imaginary terms is performed (in the coordinate direction of the measuring gradient). The quotient of the current integral and the real term of the associated pixel is an accurate measure of the time constant T2 in the relevant pixel.

Abstract: A method is provided for generating an improved torque-drag model for at least the collar portion of the drill string in a directional oil or gas well. The techniques of the present invention determine the stiffness of incremental portions of the drill string, and uses this information, the borehole clearance, and the borehole trajectory to determine the contact locations between the drill string and the sidewalls of the well. The contact force at these determined locations can be calculated, taking into consideration all significant kinematic, external, and internal forces acting on that incremental portion of the drill string. More acurate torque-drag analysis provided by the improved model of the present invention assists in well planning, prediction, and control, assists in avoiding drilling problems, and reduces total costs for the well.

Abstract: A method of exploring for hydrocarbons is disclosed wherein core is obtained over substantially the entire length of a well and substantially all lithologies represented within the core are analyzed at a core analysis facility located adjacent the well. A measurement of a plurality of physical properties of the core are made promptly after the core is removed from the well. Thereafter, from the measurement of these physical properties, a depth correlated record is generated, and is used (a) to adjust the drilling plan for that well while it is being drilled, (b) used as inputs into other exploration processes, such as seismic surveys, magnetic surveys and gravity surveys, or (c) used for correlation with other depth correlated records obtained from other wells.

Abstract: Downhole measurements are made for accurately determining whether or not a core barrel contains an appropriate amount of core sample before retrieval of the coring tool is attempted. This is accomplished by using a known apparatus for measuring downhole weight on bit (WOB) at the beginning of a coring run to make a first measurement corresponding to the weight of all drillstring components suspended below the measurement point at a selected depth. Thereafter, the coring tool drills down the length of the core barrel. When sufficient drilling takes place to obtain a core, the drillstring is pulled up to the same depth as the measurement and a second measurement is taken. After correcting the data for temperature changes, the difference in between the first and second measurements is obtained and compared to a calculated weight for a full core.

Abstract: A surface coil arrangement for use in a nuclear mangetic resonance apparatus includes two identically constructed surface coils arranged geometrically anti-parallel and electrically connected to each other so that radio-frequency magnetic fields which penetrate both coils do not generate any resultant (difference) current. Each surface coil is formed by a coaxial line section in a loop, with the jacket shielding of the coaxial line having a gap at one location in the loop. Both the inner conductor and the jacket shielding at one end of each section are electrically connected to the jacket shielding at the other end of that coaxial line section.

Abstract: For measurements with increased accuracy in a nuclear magnetic resonance apparatus, the detection device is equipped with one or more surface coils which act as measuring coils. To avoid mutual interference between a radio-frequency transmitting coil and the measuring coil, the measuring coil is provided with a decoupling circuit. The surface coil and the decoupling circuit form a part of a tuned circuit which is tuned to a significantly higher natural frequency during activation of the transmitting coil. On the other hand, the transmitting coil is shorted during detection with the surface coil by a low resistance shorting circuit, thereby avoiding interference with the radio-frequency transmission signals.

Abstract: MR imaging method and apparatus are disclosed in which one image is displayed such that a high-resolution image of a partial region obtained by measurement according to a low-speed sequence is inserted into a low-resolution whole image obtained by measurement according to a high-speed sequence.

Abstract: Truncation artifacts in NMR images are reduced by splicing to the truncated data extrapolated high frequency data derived from the truncated image. The truncated data is Fourier transformed into image space and processed with an edge enhancing filter. The retransformed, filtered data yields edge derived high frequency information that may augment the truncated data. The spliced truncated data and edge enhanced data are then reconstructed into an artifact reduced image. In one embodiment, the edge enhancement is performed by iterative passes of a modified Sigma filter. The spliced data is blended with the truncated data near the regions of the splice by means of a weighted average.

Abstract: Disclosed is a method of obtaining magnetic resonance signals from a body which are spatially and spectrally selective comprising the steps of applying a static magnetic field (Bo) to said body thereby aligning nuclear spins, applying a modulated magnetic gradient (G(t)) to said body, applying an RF excitation pulse (B(t)) to said body to tip said nuclear spins, said RF excitation pulse being related to said modulated magnetic gradient whereby resulting magnetic resonance signals are spatially and spectrally dependent, and detecting said magnetic resonance signals. The steps can be repeated in a multi-slice or multi-spectral acquisition mode. The steps can be repeated in a rapid gradient echo pulse sequence.

Abstract: An RF probe for use in magnetic resonance applications includes a transmitter coil for transmitting RF energy to excite a specimen and a receiver coil for sensing the RF energy absorbed or emitted by the specimen wherein the receiver coil is electrically decoupled from the transmitter coil through the geometrical shape and positioning of the receiver coil with respect to the transmitter coil. Both the transmitter and receiver coils are used to produce well defined RF magnetic fields. The technique includes the concept of physically locating multiple elements of either a transmitter or receiver coil such that the net current induced in the receiver coil is equal to zero. This technique is achieved in a frequency independent manner without orthogonally aligning the receiver coil with the transmitter coil, the coils being suitable for co-axial alignment as well as other alignments, much akin to prior art probes and thus readily adaptable to exisiting devices and protocols.

Abstract: There is disclosed a method of accurately calculating the magnetic field strength at an arbitrary position in an ESR (electron spin resonance) spectrum using Mn.sup.2+ marker. The spectrum contains an ESR signal arising from an unknown sample and an ESR signal arising from a reference sample containing Mn.sup.2+ marker. The resonating magnetic field strengths H.sub.ci and H.sub.cj of two absorption lines of the six absorption lines arising from Mn.sup.2+ are calculated from the applied microwave frequency, the nuclear spin quantum numbers m.sub.Ii and m.sub.Ij producing the two absorption lines, a predetermined g value g.sub.o intrinsic to Mn.sup.2+, and a predetermined isotropic hyperfine coupling constant A. The magnetic field strength H.sub.cx at a position of interest in the ESR spectrum is determined from the distance between the absorption lines, the distance between the position and one of the two absorption lines, and the magnetic field strengths H.sub.ci, H.sub.cj.

Abstract: A sample head (1) with cage resonator includes an insert (51) which can be introduced into the cavity formed by the conductor sections (22) of the cage conductor and which increases the electric length of the cage resonator in such a manner that the cage resonator containing the insert assumes a resonant state at a second predetermined operating frequency f.sub.1, whereas without the insert introduced, it is resonant at a first predetermined operating frequency f.sub.o. By introducing or withdrawing the insert (51), it is therefore possible to operate a sample head of this type selectively with two different frequencies corresponding to the resonance frequencies of different nuclear species, for example the proton and the fluorine resonance.

Abstract: A low-water-pressure-controlled hydrologic test using a measurement pipe containing an inner packer which is equipped with a water pressure gage at its tip is disclosed. Some water is poured into the measurement pipe in advance so as to diminish the pressure head difference between the in-pipe pressure and the pore water pressure of the rock concerned. The permeability coefficient is obtained by measuring changes in the recovered water level in terms of pressure changes. In the case of an aquiclude, the inner pressure is raised by expanding the inner packer, the permeability coefficient being obtained by detecting the changes in inner pressure. Thus, the method allows a permeability test to be conducted continuously at various depths. In addition, it helps to shorten the measurement time to a remarkable extent and enables the rock condition to be investigated without departing from the natural condition.

Abstract: A material sample representative of a subsurface formation is tested for its dynamic interaction with a coring fluid. The material sample is subjected to a pressurized and agitating coring fluid to simulate a coring operation. Thereafter the material sample is x-ray scanned to identify the extent of coring fluid invasion during the dynamic interaction of the material sample and the coring fluid.

Abstract: A method for correcting distortion of a reconstructed image caused by non-uniformity of a static magnetic field in an NMR imaging apparatus, wherein the non-uniformity of a three-dimensional static magnetic field is measured, and the measurement data is stored in the form of a matrix having a size smaller than the size of a matrix used in image reconstruction; then, data on a two-dimensional plane, corresponding to a slice plane of the reconstruction image, is taken out from the matrix, and based on that data, a distortion correcting table is produced and is enlarged to agree with the size of the matrix used in image reconstruction, so that distortion of the reconstructed image is corrected using the enlarged distortion correcting table.

Abstract: The invention relates to a method of determining the porosity of an undergound formation being drilled by a rotating drill bit mounted at the lower end of a drill string. The torque (TOR) and the weight (WOB) applied on the bit when drilling the underground formation are measured; the effect of the geometry of the drill bit on the torque and weight on bit response is determined; the porosity (phi) of the formation being drilled is derived from the measured TOR and WOB taking into account the effect of the geometry of the drill bit. Preferentially, the porosity phi is determined from the following equation:TOR=(k.sub.1 +k.sub.2.phi)WOB.sup.awhere k.sub.1, k.sub.2 and a are parameters characteristic of the geometry of the drill bit.

Abstract: A method to recover MRI signals resulting from the application of time varying gradients. The raw MRI signal is demodulated, low pass filtered, and digitized using an A/D converter sampling linearly at the Nyquist rate. The samples from the A/D converter are compiled into a vector, which is multiplied by a least squares estimator matrix (H*H).sup.- H*, where H is a matrix whose mkth element, in the case of a sinusoidal gradient, is given by ##EQU1## This multiplication is repeated for each vector of samples from the A/D converter, and the vectors resulting from the multiplication are accumulated to form the columns of a matrix, the rows of which are Fourier transformed to obtain the MRI image.

Abstract: A method of and device for the determination with high computational efficiency of spectrum parameters of a spectrum utilizes quantification and model fitting of sampling values of a signal in the time domain on the basis of a model function comprising exponentially damped sinusoids. The method starts with a coarse estimation of a number of spectrum parameters, followed by linearization of the model function and iterative estimation of the coarsely estimated parameters and further parameters, utilizing a least-squares optimization procedure where inner product terms are brought into analytic form and are preferably recursively determined.

Abstract: A method for determining at wellsites the solids content of drilling fluids by high-frequency dielectric measurements including: preparing samples of the drilling fluid, of the drill cuttings from the formation, and of each solids-additives type added to the drilling fluid for uniform dielectric constant measurements at preselected frequencies and obtaining the solids content in accordance with the relationship between the dielectric constant measurements of the drilling fluid-solids, drill cuttings, and each of the solids-additives type. In accordance with the method of the invention two levels of determination are possible. These levels of determination depend upon whether the quantities of solids-additives type added to the drilling fluid are known.