Abstract: Apparatus for obtaining horizontal and/or vertical permeability measurements through a probe having an elongate aperture. The invention uses the elongate aperture in the probe to orient fluid flow in an earth formation horizontally or vertically. The elongate aperture is approximated through the use of a single elongate opening or through the use of a group of aligned openings of varying shapes. Measurements can be taken at different orientations by including additional probe openings along more than one axis.

Abstract: Methods and related apparatus for conducting shear slowness logging are set forth. The methods broadly comprise: detecting dispersive waves such as flexural or Stoneley waves; Fourier transforming the received signals; backpropagating the Fourier transformed signals according to equations using different dispersion curves; stacking the backpropagated signals; and finding semblances in order to choose the dispersion curve of maximum semblance and thereby identifying the shear slowness of the formation. Formation shear slowness may be plotted over borehole depth. Different embodiments are set forth. In one preferred embodiment (QDSTC), prior to Fourier transforming, the signals are stacked according to a previous estimation of slowness (S.sub.0), and are windowed for maximum energy. The reduced set of data in the window are then extracted for Fourier transformation, and prior to backpropagation, multiplied by S.sub.0 to reset them for backpropagation and stacking.

Abstract: A method and apparatus for spatially filtering a signal set to enhance interface echoes representing a borehole configuration. The spatial filtering technique provides information regarding the various interfaces formed between materials in the borehole environment, as well as thicknesses of the various materials present in the borehole. Further, the presence of channels formed during the cementing procedure are detected.

Abstract: A borehole tool has a source probe in fluid contact with the borehole wall, a fluid flow line for bringing fluids to and from the source probe, two injection fluid chambers containing clean oil and clean water and in fluid contact with the fluid flow line, at least one sample chamber for receiving fluid from the formation, valves for selectively routing the formation fluids and the clean oil and water through the fluid flow line, at least one pressure controller for controlling whether fluid is to be injected or withdrawn from the formation via the source probe, and a pressure gauge for measuring the pressure seen at the source probe. Permeability measurements are made by sequentially injecting one clean fluid into the formation, followed by a cleaning of the line with the other fluid which was not injected, followed by the injection of the other fluid into the formation. The order in which the oil and water are injected is based on the type of mud used for drilling.

Abstract: Methods for distinguishing among oil samples, and more particularly between a fluid containing oil base mud and formation oil samples are described. The methods all rely on the discovery that the optical absorption spectrum of all crude oils in the visible and near infrared spectra can be described according to the equation OD=ae.sup.Eb, where (OD) is a measured optical density, (b) is a value between 0.37 and 0.55 chosen according to the wavenumber (E) and can be chosen as a constant equal to 4.6.times.10.sup.-4 cm, and (a) is an unknown which classifies the crude oil. By making measurements and solving for (a), a crude oil can be classified. In a flow stream which has a changing oil content, such as may be obtained by a borehole tool which obtains fluid samples from the formation, by monitoring the unknown (a), a determination may be made as to when a formation oil is being obtained as opposed to a mud filtrate.

Abstract: A single crystal scintillator and apparatus for prospecting underground strata using the scintillator is described. The single crystal scintillator is a cerium doped gadolinium silicate compound of the formula:Gd.sub.2-(x+y) Ln.sub.x Ce.sub.y SiO.sub.5wherein Ln is Sc, Tb, Lu, Dy, Ho, Er, Tm, or Yb; 0.03.ltoreq.x.ltoreq.1.9; and 0.001.ltoreq.y.ltoreq.0.2.

Abstract: Methods and apparatus are described for simultaneously acquiring time-domain (e.g., compressional) and frequency-domain (e.g., monopole Stoneley and/or dipole shear) borehole logs which are separated by frequency filtering. Monopole (Stoneley) data and dipole (shear) data are acquired simultaneously using discrete-frequency sonic emission, preferably at distinct frequencies to avoid cross-mode interference. A preferred embodiment combines discrete-frequency dipole sonic emission at low frequency (up to 5 kHz) to log formation shear wave, high frequency (5 to 30 kHz) time-domain monopole emission with first-motion detection to log formation compressional wave, and discrete-frequency monopole emission at low frequency (below 5 kHz) to log borehole Stoneley wave. The measurements of compressional, shear and Stoneley can be transmitted uphole using a small telemetry bandwidth.

Abstract: Fluid flow measurements are made in situ using a repeat formation tester with a modified probe aperture, or on rock samples using a mini-permeameter with a modified probe aperture. The modified probe aperture has an elongate cross-section, such as elliptic or rectangular. A first flow measurement is made with the longer dimension of the probe aperture in a first orientation (e.g., horizontal or vertical) with respect to the formation bedding planes. A second flow measurement is made with the probe aperture orthogonal to the first orientation, or with a probe aperture of non-elongate (e.g., circular) cross-section. Simultaneous equations relating values of known and measured quantities are solved to obtain estimates of local horizontal and/or vertical formation permeability.

Abstract: Methods for determining hydraulic properties of a formation surrounding a borehole are disclosed. The methods use a borehole tool preferably having a first probe for injecting fluid into a formation or obtaining fluid from the formation, a second probe vertically displaced relative to the first probe, and a third probe azimuthally displaced relative to the first probe. The method generally comprises: varying the pressure at the first probe of the borehole tool; measuring pressures at the second and third probes resulting from the varying of pressure at the first probe; and utilizing the pressures measured at the second and third probes to determine values over time of a function related to the hydraulic properties of the formation. This function is a function of the geometry and rock and fluid properties of the formation but is independent of the manner in which the pressure is varied at the first probe.

Abstract: A slot antenna has a square aperture and two current probes at angles to each other in the aperture. The two current probes are excited simultaneously or separately with different signals. By adjusting the amplitude or phase of the signals in the current probes, the angle of the magnetic moment of the antenna can be adjusted. An array of such antennas in an electromagnetic propagation tool for a well-logging device simultaneously provides better standoff performance by adjusting the magnetic moment to be parallel to a borehole axis, and better image response by adjusting the magnetic moment to be perpendicular to the formation bed. The array can be excited to function as an endfire and broadside array of an electromagnetic propagation tool.

Abstract: The present invention is directed to utilizing data indicative of formation resistivity and calculating the width and depth of a fracture therefrom. In the preferred embodiment, the present invention employs data acquired from a formation microscanner tool. Potential fracture locations are detected for acquired formation microscanner tool data preferably by taking into account the relatively slowly varying conductivity changes in the rock matrix, and separating them out from the high and narrow peaks generated by fractures. Each potential fracture location can be depicted as current from the formation microscanner tool versus azimuth, wherein the current measured by the formation microscanner tool is essentially flat for the formation but peaked for potential fracture locations.

Abstract: A tool which contains a pulsed accelerator neutron source and means for making timing measurements of the thermal neutron response in a localized portion of the environment immediately surrounding the borehole. Formation sigma is determined by parameterizing the detected thermal neutron decay curve, preferably with a diffusion model similar to that known in the art for determining formation sigma on the basis of gamma ray time distributions. In a more comprehensive embodiment of the present invention, which includes a gamma detector in the tool, formation sigma can be measured in parallel using both gamma ray and thermal neutron decay characteristics. Deviations between the neutron and gamma-based signals that occur as the tool traverses the borehole, provide useful indications of local effects immediately surrounding the borehole.

Abstract: A geophysical prospecting method comprises injecting signal energy in the form of at least two pseudo-random pulse sequences of the complementary sequence type into an underground formation. Next, the signal energy is detected after it has been attenuated by passing through the underground formations in the form of response signals. The response signals are correlated with reference signals comprising at least two pseudo-random binary sequences to yield correlations. The correlations are summed so that the resultant signal which corresponds to the subsurface response signal does not have secondary lobes. The method is applicable to seismic prospecting and more particularly to cross-well seismic surveying. It is also applicable to acoustic prospecting for logging measurements. In a preferred embodiment, the pseudo-random sequences comprise a pair of Golay sequences.

Abstract: A technique is disclosed for determining properties of an anisotropic elastic medium, such as earth formations. Acoustic waves are established in the medium. At several spaced locations in the medium, there are measured at least two orthogonal components of acoustic waves which have propagated through the medium. For positions corresponding to a plurality of adjacent ones of the spaced locations, there are computed model composite waves which would result from the superposition of a plurality of model acoustic waves, each having selected model parameters. The model acoustic waves include a plurality of model acoustic shear waves and the model parameters include model velocities and model polarizations for each of the model acoustic shear waves. An error value is determined, the error value depending on the differences, at each of the plurality of adjacent ones of the locations, between measured wave components and the model composite wave. The model parameters are then modified.

Abstract: In a form of the disclosure, electromagnetic propagation logging measurements are made for several magnetic moment directions of the electromagnetic energy, and can be examined and/or processed retrospectively in order to select the logging information which has a particular desired characteristic, such as the sharpest imaging of bed boundaries. By scanning the magnetic moment over a wide range of angles, one is assured of obtaining logging information that has a desired attribute, such as image sharpness. This can be determined by viewing a recorded log and/or by automatically processing the log data. Information from other ones of the several logs may be useful in optimizing other attributes, such as standoff immunity or signal-to-noise ratio.

Abstract: A borehole apparatus detects the presence of gas within a formation fluid sample. A light source transmits light rays to an interface between the fluid sample and the flow line. The interface reflects the light rays toward a detector array. The detector array detects light rays having angles of incidences extending from less than the Brewster angle to more than the critical angle for gas. A data base stores information concerning the Brewster angle and critical angle of gas for a plurality of gas volume categories. A processor determines the percentage of gas present in the formation fluid sample and categorizes the fluid sample as high as, medium gas, low gas, and no gas based on the signal from the detector array and the information from the data base.

Abstract: The apparatus includes a pad (20) pressed against the wall of a borehole (12), the pad comprising a plurality of detecting devices (42, 43, 44, 45) disposed in alignment along the longitudinal direction of the borehole. Each detecting device includes a housing (112, 113) having complementary ends fitted with electrical connectors. The end of one housing (112) is extended by first skirts (117, 118) suitable for interfitting between second skirts (121) of the complementary end of the housing (113) of an adjacent detecting device. An annular element (111) and screws (120, 122) fixed to complementary ends together thus constituting a rigid pad (20) which can be disassembled.

Abstract: A particle accelerator comprises a Cockcroft-Walton voltage multiplier that provides linear axial and radial fields. The Cockcroft-Walton voltage multiplier includes capacitors that are arranged radially relative to one another, such that a linear voltage increase occurs between the capacitors. The particle accelerator is made by placing conductive foils on an insulating sheet, connecting the foils as a Cockcroft-Walton voltage multiplier, and rolling the insulating sheet with the foils into a cylinder to form the radially arranged capacitors.

Abstract: A borehole apparatus detects the presence of gas within a formation fluid sample. A light source transmits light rays to an interface between the fluid sample and the flow line. The interface reflects the light rays toward a detector array. The detector array detects light rays having angles of incidences extending from less than the Brewster angle to more than the critical angle for gas. A data base stores information concerning the Brewster angle and critical angle of gas for a plurality of gas volume categories. A processor determines the percentage of gas present in the formation fluid sample and categorizes the fluid sample as high gas, medium gas, low gas, and no gas based on the signal from the detector array and the information from the data base.

Abstract: A borehole apparatus for analyzing the composition of a formation fluid includes a chamber that contains the fluid, and a light source that directs light through the fluid in the chamber. The optical path of the light is modified such that an output fiber optic bundle receives indirect light through the fluid. One embodiment comprises a diffuser in the optical path, which forward scatters the light to the output fiber optic bundle. Another embodiment comprises the misalignment of an input fiber optic bundle relative to the output fiber optic bundle. Collimators can be subsituted for the fiber optic bundles.