Abstract: A method for enhancing measurement resolution is disclosed. In one embodiment, the method includes (1) obtaining multiple measurement samples at each of multiple positions along a borehole; (2) extracting reference index samples from the set of measurement samples; (3) determining a difference between each of the reference index samples and corresponding modeled index samples; and (4) updating a set of enhanced index samples based on the difference. The index samples are preferably chosen to be representative of the measurement samples obtained at each position, and accordingly, may be selected ones of the measurement samples, or alternatively, may be averages of the measurement samples. The aforementioned modeled index samples may be found from application of a predetermined tool response to the enhanced index samples, which in turn, may be found by iteration.

Abstract: Techniques are provided to transform attenuation and phase measurements taken in conjunction with a drilling operation into independent electrical parameters such as electrical resistivity and dielectric values. The electrical parameters are correlated with background values such that resulting estimates of the electrical parameters are independent of each other. It is shown an attenuation measurement is sensitive to the resistivity in essentially the same volume of an earth formation as the corresponding phase measurement is sensitive to the dielectric constant. Further, the attenuation measurement is shown to be sensitive to the dielectric constant in essentially the same volume that the corresponding phase measurement is sensitive to the resistivity. Techniques are employed to define systems of simultaneous equations that produce more accurate measurements of the resistivity and/or the dielectric constant within the earth formation than are available from currently practiced techniques.

Abstract: A resistivity tool and associated method include measuring the phase shift of an electromagnetic signal at different locations. Preferably, this is accomplished by a resistivity tool having three receivers. The difference of the phase shifts at the different locations indicates with precision the depth in a borehole of a bed boundary. The preferred resistivity tool also yields improved radial resolution.

Abstract: A shield apparatus for use in conjunction with a well tool to selectively attenuate one or more electromagnetic energy field components as the components interact with the shield. The shield composed of a flexible strip or conductive body and comprising at least one sloped slot or sloped conductive element therein. The shield being adapted to surround an antenna mounted on a well tool. A method for rotating the axis of the magnetic dipole of a transmitter or receiver coil. A method for winding and shielding an electric coil such that the resultant coil emits or receives selected electromagnetic energy field components.

Abstract: Resistivity data acquired at two different epochs using different types of tools are jointly inverted. For example, a multiple propagation resistivity (MPR) tool is run first, preferably at several frequencies and several transmitter-receiver spacings. At a later epoch, an induction tool may be run, preferably on a wireline. The joint inversion process identifies bed boundaries based on inflection points in the propagation resistivity and induction logging raw data. An initial guess for an uninvaded earth model is generated using the selected bed boundaries and the apparent raw resistivity values. An inversion run using shallow measurements of propagation resistivity logging data is performed to estimate a resistivity structure representative of the near borehole zone resistivity (invaded zone). The bed boundary positions of the layers are also updated as part of the inversion process. Synthetic data for both the shallow and deep measurements are generated to delineate the invasion zones.

Abstract: A shield apparatus for use in conjunction with a well tool to selectively attenuate one or more electromagnetic energy field components as the components interact with the shield. The shield composed of a flexible strip or conductive body and comprising at least one sloped slot or sloped conductive element therein. The shield being adapted to surround an antenna mounted on a well tool. A method for rotating the axis of the magnetic dipole of a transmitter or receiver coil. A method for winding and shielding an electric coil such that the resultant coil emits or receives selected electromagnetic energy field components.

Abstract: A shield apparatus for use in conjunction with a well tool to selectively attenuate one or more electromagnetic energy field components as the components interact with the shield. The shield composed of a flexible strip or conductive body and comprising at least one sloped slot or sloped conductive element therein. The shield being adapted to surround an antenna mounted on a well tool. A method for rotating the axis of the magnetic dipole of a transmitter or receiver coil. A method for winding and shielding an electric coil such that the resultant coil emits or receives selected electromagnetic energy field components.

Abstract: A highly accurate, fully compensated, high spatial resolution, wave propagation system for measuring dielectric constant and resistivity of fluids or solids in a cylindrical enclosure and method for measuring well core characteristics in-situ or in a laboratory. One embodiment of the invention relies on waves propagated from transmitters above and below two spaced receivers which transmit and receive electromagnetic waves via slots on the inner periphery of a cylinder structure. The data is then processed with a CPU either down hole for later retrieval or on the surface for real-time monitoring.

Abstract: A method and apparatus for evaluating the resistivity of earth formations surrounding a borehole, particularly high-contrast thin-layer formations or at high dip angles. The method involves positioning a pair of transmitters and a pair of receivers within the borehole, the receivers or transmitters adhering to specific spacing limitations, alternately transmitting electromagnetic energy of a particular frequency and receiving voltage data associated with the transmitted energy. Multiple voltage data are acquired and a representation of a resistivity or conductivity profile is created from a formulated difference of the data from a particular depth and/or neighboring depths. The apparatus forms part of a well logging system including a well tool adapted to be moveable through a borehole. The apparatus being coupled to the well tool and adapted with means to input voltage data developed by the receivers disposed on the well tool.

Abstract: The present invention relates generally to the use of polyaryletherketone-based thermoplastic materials in high pressure, high temperature, production logging applications. A polyaryletherketone resin bonded with glass fibers is formed into a housing for formation evaluation sensors permanently located downhole. The housing is constructed by any of the following processes: filament winding, fiber placement, or compression molding or injection molding. When used in a production well, the housing encloses the formation evaluation sensors and protects the sensors from borehole fluids. Housing properties can be modified with changes in materials added to the resin in order for the housing to function as casing or coiled tubing. This would allow wireline or logging-while-drilling conveyed sensors passing through the casing or coiled tubing to sense the formation and borehole fluid properties.

Abstract: Methods and apparatus for making directional measurements of earth formations surrounding a borehole. New antenna coil shield designs are utilized to provide selective attenuation of at least one electromagnetic energy field component as the component interacts with the shield. The new shields are implemented in several downhole tool configurations to provide azimuthally focused formation measurements. In effect, the new shield filters interacting electromagnetic energy field components to pass those components corresponding to a magnetic dipole oriented at an angle from the tool axis. The shields thereby alter a coil's envelope of influence to electromagnetic energy. The new shields also form part of a system for making directional measurements while drilling.

Abstract: A morphological survey of geological formations traversed by a borehole includes constructing, from an initial image of the wall of the borehole representative of variations in a physical parameter of the formation in the longitudinal direction of the borehole (“depth”), and in the peripheral direction of the borehole wall (laterally), a “crossing-component image.” The cross-component image includes only those components of the parameter that extend all the way across the initial image from one side of the image to the other. The survey includes determining variations in one or more attributes relating to the parameter in the crossing-component image as a function of depth. The variations providing information relating to morphology to indicate solid zones, bedded zones, or different types of heterogeneous zones, for example.

Abstract: A shielding method and apparatus for an antenna disposed on an elongated support adapted for disposal within a borehole. The shield providing predetermined attenuation of one or more electromagnetic energy field components as the field components interact with the shield. The shield composed of a flexible strip or cylindrical body and respectively comprising a transverse conductive element or a transverse slot therein. The shields being adapted to cover an antenna mounted on the support. The shields being compatible for use in conjunction with saddle, tilted coils or multi-layered tri-axial coils to produce a pure transverse magnetic dipole electromagnetic field. The shields are also used in methods for shielding an antenna disposed on a support to provide predetermined attenuation of an electromagnetic field component as the field components interact with the shield.

Abstract: A resistivity tool for use in an LWD system includes an asymmetric transmitter design with multiple transmitters capable of generating EM signals at multiple frequencies. A pair of receivers are positioned at one end of the transmitter array to detect the EM signals after they have traversed the region in the vicinity of the borehole. A calibrating transmitter is positioned between the receivers, which can be used in two different modes of operation. In a first mode, the calibrating transmitter is used to calibrate the receivers for thermal drift. In this calibration mode, an attenuation correction and phase shift correction can be calculated to correct for thermal drift of the receivers while the resistivity tool is in the borehole. Thus, the thermal drift of the receivers can be re-calibrated as often as desired while the tool is in the well. In a second mode of operation, the calibrating receiver may be used to measure the resistivity of the drilling mud in the borehole.

Abstract: The present invention is directed to a method and apparatus for determining the dip angle and horizontal and vertical conductivities of a wellbore during drilling operations. If the dip angle is not known, the present invention allows for the use of multifrequency measurements and a model which maps dielectric permitivities to conductivities to calculate the horizontal conductivity, the vertical conductivity, the horizontal dielectric permitivity, the dielectric permitivity, and the dip angle. If the dip angle is known, the present invention allows a multifrequency tool to be utilized alone to calculate the horizontal conductivity, the vertical conductivity, the horizontal dielectric permitivity, and the vertical dielectric permitivity.

Abstract: A resistivity tool suitable for use in a borehole and configured to obtain a resistivity radial profile at multiple depths of investigation in a geological formation comprises a receiver pair and an array of transmitters. The distance of each transmitter from the receivers corresponds to a particular depth of investigation into the formation. Using as few as two transmitters, the resistivity tool derives resistivity values at any number of depths of investigation, including depths of investigation that do not correspond to transmitter/receiver spacings on the tool. A measurement processor combines signals received from the existing transmitters using linear interpolation, geometric interpolation, and/or other techniques to derive the resistivity measurements.

Abstract: An apparatus and method for implementing azimuthal capabilities on electromagnetic wave resistivity well logging tools. The apparatus comprises a structurally simple antenna shield positioned around either the transmitting or receiving antennas, or both, positioned on the well logging tool on the drill string. The shields partially surround the tool and provide an electromagnetic barrier for either the transmission or reception of electromagnetic waves, as the case may be. Positioned on the shield are appropriately placed and sized windows through which electromagnetic waves may either be transmitted or received, depending upon the function of the antenna that the shield surrounds. Variations in window dimensions allow optimization of the device for use in conjunction with a variety of formations and a variety of drill mud characteristics.

Abstract: A wireline, coiled tubing, and measurement while drilling resistivity tool having three or more receivers is disclosed. This results in a tool capable of gathering substantial resistivity data about a subterranean formation while being drawn quickly past a borehole wall. One embodiment of this resistivity tool includes four receivers and a pair of transmitters, resulting in six resistivity measurements from each firing of a transmitter. The transmitters are arranged to obtain a regularly spaced series of resistivity measurements. The transmitters may be fired at two or more frequencies to result in further information about the formation. Another embodiment of this resistivity tool places its transmitters and receivers to obtain a number of redundant resistivity readings, resulting in error checking and increased reliability. For enhanced performance, transceivers may also be used. An analogous method is also disclosed.

Abstract: An azimuthally tunable resistivity measurement tool is provided. In one embodiment, the tool comprises a set of three skewed receiver antennas and a transmitter antenna. The three skewed receiver antennas are oriented in equally-spaced azimuthal directions to give them preferential sensitivity in those directions. The transmitter antenna transmits a radio-frequency signal that propagates through the formation surrounding a borehole. The signals from the three receiver antennas can be measured and combined to synthesize the signal that would be received by a virtual antenna oriented in any desired direction. Accordingly, virtual receivers oriented perpendicular to the tool axis and with variable azimuthal orientations can be synthesized. The orientation of such a virtual receiver that has a maximized receive signal amplitude can be used to identify the direction of a nearby bed boundary, and the maximized amplitude can be used to estimate the distance to the boundary.

Abstract: This invention is directed to a downhole method and apparatus for simultaneously determining the horizontal resistivity, vertical resistivity, and relative dip angle for anisotropic earth formations. The present invention accomplishes this objective by using an antenna configuration in which a transmitter antenna and a receiver antenna are oriented in non-parallel planes such that the vertical resistivity and the relative dip angle are decoupled. Preferably, either the transmitter or the receiver is mounted in a conventional orientation in a first plane that is normal to the tool axis, and the other antenna is mounted in a second plane that is not parallel to the first plane. Although this invention is primarily intended for MWD or LWD applications, this invention is also applicable to wireline and possible other applications.

Abstract: An apparatus and method for determining a location and an orientation of an underground boring tool by employment of a radar-like probe and detection technique. The boring tool is provided with a device which generates a specific signature signal in response to a probe signal transmitted from above the ground. Cooperation between the probe signal transmitter at ground level and the signature signal generating device provided at the underground boring tool results in accurate detection of the boring tool location and, if desired, orientation, despite the presence of a large background signal. Precision detection of the boring tool location and orientation enables the operator to accurately locate the boring tool during operation and, if provided with a directional capacity, avoid buried obstacles such as utilities and other hazards. The signature signal produced by the boring tool may be generated either passively or actively, and may be a microwave or an acoustic signal.

Abstract: Earth formation evaluation for detection of hydrocarbon fluids is carried out by a microwave frequency range sensor (antenna or wave guide) disposed in the face of a diamond or PDC drill bit configured to minimize invasion of drilling fluid into the formation ahead of the bit. The sensor is connected to an instrument disposed in a sub interposed in the drill stem for generating and measuring the alteration of microwave energy. In particular, the dielectric constant of the earth formation in a zone which is substantially uninvaded by drilling fluid may be detected and compared with density and/or porosity logs to determine the presence of hydrocarbons in relatively thin layers of formation material.

Abstract: A directional induction logging tool is provided for measurement while drilling. This tool is preferably placed in a side pocket of a drill collar, and it comprises transmitter and receiver coils and an electromagnetic reflector. The reflector, which may be a layer of highly conductive material placed between the coils and the body of the drill collar, serves to focus the electromagnetic fields generated and sensed by the tool in the direction away from the reflector, thus providing a directional response to formation conductivity with a relatively high depth of investigation. In preferred embodiments of the invention, magnetically permeable cores are placed within the coils to concentrate the magnetic fields that pass through them. Circuitry is described for balancing the mutual inductive coupling of the coils by injecting a direct current signal through one or more of the coils, which alters the magnetic permeability of the core material.

Abstract: An adjacent well telemetry system for changing the operational state of a downhole device and a method for use of the system is disclosed. The system comprises an electromagnetic transmitter disposed in a wellbore that transmits an command signal that is received by an electromagnetic receiver disposed in an adjacent wellbore. The electromagnetic receiver sends the command signal to an electronics package that generates a driver signal in response to the command signal that prompts the downhole device to change operational states.

Abstract: A retrievable resistivity logging system is provided for obtaining directional resistivity information while drilling (e.g., in an MWD system). The information obtained by this system can be used to determine the proximity of resistivity discontinuities and for use in steering the progress of the wellbore in the presence of geological boundaries of interest. In preferred embodiments, the logging system comprises passive transmitter and receiver electrodes built into subs that are incorporated into the drillstring, and a retrievable instrument cartridge that comprises spring loaded contacts that engage contact surfaces in the subs to connect the electrodes to the cartridge. In some embodiments, the cartridge comprises toroidal transformers coaxial to the cartridge for generating the survey current and for detecting the received current from the receive electrode.

Abstract: The system of the present invention includes measurement instrumentation that is located in or near the drill bit and used in a measuring-while-drilling system. The instrumentation can be located in a bit box, an extended sub between the drilling motor assembly and the bit box or in the drill bit. The drill bit is connected directly to the bit box or extended sub. The close proximity of the instruments to the drill bit allows for more reliable and useful measurements of drill bit, drilling and formation conditions. The bit box houses instruments that measure various downhole parameters such as inclination of the borehole, the natural gamma ray emission of the earth formations, the electrical resistivity of the earth formations, and a number of mechanical drilling performance parameters. Sonic or electromagnetic signals representing these measurements are transmitted uphole to a receiver associated with receiving equipment located uphole from the drill bit.

Abstract: A method for generating a flow profile of a wellbore whereby a resistivity tool is run through the wellbore, while the wellbore is being drilled, to sequentially measure and record, at each of a sequence of selected points along the wellbore, a sequential series of resistivities measured while drilling (MWD). Fluid from the wellbore is then allowed to permeate into the formation. The resistivity tool is then run through the wellbore, after the drilling mud has permeated into the formation, to sequentially measure and record, at substantially the same points at which the MWD resistivity measurements were made, a sequential series of resistivities measured after drilling (MAD). For each point, the arithmetic difference between the MWD resistivity and the corresponding MAD resistivity recorded for the respective point is calculated.

Abstract: A method and apparatus is disclosed for determining the properties of formations surrounding an earth borehole that have been invaded by borehole fluid to form an invaded zone.

Abstract: Apparatus for sensing the resistivity of geological formations surrounding a borehole includes a tubular body member (1) which is adapted to form a portion of a length of drill string. An antenna (10) is mounted within the body member (1) and the body member (1) has apertures (2) adjacent to the antenna (10) to permit an electro-magnetic signal to pass through the body member (1) after transmission from, or for reception by, the antenna (10).

Abstract: An antenna includes a transmitter including a first transmit coil wound in a first direction. A second transmit coil is electrically coupled to the first transmitter and wound in a second direction opposite to the first direction.

Abstract: An apparatus and method for determining a location and an orientation of an underground boring tool by employment of a radar-like probe and detection technique. The boring tool is provided with a device which generates a specific signature signal in response to a probe signal transmitted from above the ground. Cooperation between the probe signal transmitter at ground level and the signature signal generating device provided at the underground boring tool results in accurate detection of the boring tool location and, if desired, orientation, despite the presence of a large background signal. Precision detection of the boring tool location and orientation enables the operator to accurately locate the boring tool during operation and, if provided with a directional capacity, avoid buried obstacles such as utilities and other hazards. The signature signal produced by the boring tool may be generated either passively or actively, and may be a microwave or an acoustic signal.

Abstract: A well logging method and apparatus are disclosed for determining borehole corrected formation resistivity, borehole diameter, and downhole borehole fluid (mud) resistivity with improved accuracy. A logging device in the borehole transmits electromagnetic energy from a transmitter, which energy is received at receivers on the logging device. The phase and amplitude of the received energy are measured at the receivers and a phase shift, phase average, and attenuation are associated with the transmitter-to-receivers spacing. The process is then repeated for a plurality of further transmitters having different spacings from the receivers. A formation and borehole model having model values of borehole corrected formation resistivity, borehole diameter, and borehole fluid resistivity is generated.

Abstract: A propagation resistivity measurement-while-drilling device is used to measure borehole environmental parameters along with electromagnetic properties of the formation. Multiple transmitter-receiver pairs operating at one or more transmitter frequencies are used to obtain a set of amplitude and phase measurements. A model of the response of the borehole instrument in varying formation and borehole conditions is also utilized. Formation and borehole parameters of interest are selected by the analyst. The measured amplitude and phase data set is then combined with the model of the tool response to obtain the selected parameters of interest.

Abstract: A method is disclosed for determining the horizontal resistivity, vertical resistivity, and dip of formations surrounding a borehole, comprising the following steps: (a) suspending a logging device in the borehole; (b) transmitting electromagnetic energy from a transmitter location on the logging device, and receiving the transmitted electromagnetic energy at receiver locations on the logging device for a first transmitter-to-receivers spacing associated with the transmitter and receiver locations; (c) determining, from the received electromagnetic energy, measurement characteristics associated with the first transmitter-to-receivers spacing; (d) repeating steps (b) and (c) for a plurality of further transmitter-to-receivers spacings to obtain measurement characteristics for the plurality of further transmitter-to-receivers spacings; (e) generating a model of anisotropic formations that has horizontal resistivity Rh, vertical resistivity Rv, and a Dip angle with respect to a borehole reference; (f) selecting

Abstract: An arrangement of two closely spaced transmitters and two spaced apart receivers symmetrically disposed about the transmitters in a measurement while drilling tool avoids the effects of mutual coupling between the receivers. In one method of operation of the transmitters, each transmitter is sequentially activated while the other transmitter is decoupled to eliminate mutual coupling, and the recorded signals processed to take advantage of reciprocity relations. In another method of operation, both transmitters are operated simultaneously with one relative polarity and then with another relative polarity, to eliminate the effects of mutual coupling and to take advantage of reciprocity relations.

Abstract: A method of determining the conductivity of earth formations penetrated by a wellbore. The method includes inserting an induction well logging instrument into the wellbore. The instrument includes a transmitter, a source of alternating current connected to the transmitter, and a receiver. The transmitter is energized with the alternating current, voltages induced in the receiver are recorded, and area enclosed with respect to a baseline, by voltage peaks present in the recorded voltages is determined. The enclosed area corresponds to the conductivity.

Abstract: A propagation resistivity measurement-while-drilling system is used to determine the resistivity (or conductivity) of the conate formation fluid, the dielectric constant of the dry rock matrix, and the water filled porosity of the formation. One or more transmitter-receiver pairs are utilized with the transmitter component of the transmitter-receiver pairs operating at a plurality of frequencies. Water filled porosity measurements can be combined with an independent measurement which responds to the total fluid porosity of the formation to obtain a measure of formation hydrocarbon saturation in fresh or saline conate water environments.

Abstract: The present invention is directed to a measurement-while-drilling logging tool which includes a minimum number of analog electrical and electronic components, and which instead utilizes digitally-controlled electronic and electrical components to obtain an accuracy which is not possible utilizing prior art measurement-while-drilling logging tools. Additionally, the present invention allows for calibration operations to be conducted before, during, and after logging operations. Preferably, the calibration operations are performed periodically or intermittently during logging operations, and recorded, to be utilized later in explaining any irregularities in the log data. This calibration operation during drilling operations is not found in prior art devices, and is rendered practical by the utilization of digitally-controlled electrical and electronic components in lieu of analog components which are traditionally utilized in logging tools.

Abstract: Method and an apparatus for determining a vertical distance between a first marker and a second marker embedded in a formation traversed by a borehole so as to quantify the occurrence of earth layer compaction or subsidence. The markers are implanted within a formation and their relative position is monitored over time to detect the presence of formation subsidence and compaction. A tool having three or more detectors adapted to sense signals emitted from the markers is positioned proximate the markers, where the detectors are separated from each other by a known vertical spacing. The tool is positioned at least at three elevations such that a reference elevation of a reference portion of the tool is determined when (a) the first detector detects a signal emitted from the first marker, (b) the second detector senses a signal emitted from the second marker, and (c) the third detector detects a signal emitted from one of the markers.

Abstract: The porosity and permeability of a geological formation (2) are determined on the basis of an electrofiltering phenomenon by exploiting the existence of non-linear electrofiltering phenomena. One or two pressure generators (11 ) are used to propagate a pressure wave in the formation. Electrodes (14, 15) applied against the wall of the formation pick up the electric response of the formation. The detection of a resonance frequency or a phase shift corresponding to an extremum of the electric response of the formation makes it possible to calculate the porosity or permeability of the formation or find their values from charts.

Abstract: A logging apparatus is provided for use in a wellbore for measuring an attribute of at least one of the wellbore and a surrounding formation, when coupled to a wellbore tubular expended in the wellbore. The logging apparatus includes a housing, at least one transmitter, and at least one receiver. The transmitter is carried by the housing and is individually and selectively operable for producing electromagnetic interrogating signal at selected interrogation frequency for passage to the wellbore and surrounding formation. The receiver is carried by the housing in a selected position relative to the transmitter, and is tuned to receive electromagnetic signals at the interrogation frequency to the exclusion of other frequencies.

Abstract: A method for locating underground cylindrically symmetrical magnetic sources, particularly boreholes, from magnetic field measurements. The method is based on the shape of magnetic field produced by magnetic materials with cylindrical axes. As the field caused by the magnetic source always points away from or towards its cylindrical axis, lines extended from magnetic field vectors caused by the magnetic source will always pass through the axis. Numerical techniques are used to find the common line to all the extended magnetic field vectors and thus calculate the axis of the magnetic source.

Abstract: The present invention is directed to an improved logging apparatus. The logging apparatus includes transmitters, receivers, and a controller member. The controller member is utilized to selectively energize the transmitters to generate an interrogation signal. The receivers are utilized to obtain measurements of the interrogation signal. The controller member can be utilized to substantially simultaneously process the recorded samples--such as by mathematically combining a plurality of measurements in order to obtain a measure of an attribute value which relates to at least one of the wellbore and surrounding formation.

Abstract: A sealed, modular downhole antenna for measuring electrical characteristics of wellbore fluids and formations. An antenna includes a thin-walled curved metal tube, which houses coil of a length of conductive wire. The wire may be insulated by an insulating coating, as well as a filler that resides in the tube. The tube includes a coupling gap, to facilitate coupling electromagnetic energy through the tube, to and from the conductive wire. The tube also has a wall opening, for ends of the wire to attach to an adapter-connector. The adapter-connector includes suitable features for modular connection to an electrical cable, electrical connectors, or other electrical equipment. Features of the invention may be provided to ensure that such connection is resistive to the high pressures that are often encountered downhole. In this respect, the tube may be also coated with a sealant layer, to hermetically seal the tube, coupling gap, and junction between the adapter-connector and the tube.

Abstract: Formation anisotropic properties are determined using knowledge of the borehole dip angle and an induction logging instrument to obtain two formation derived resistivities. Separate shale layer anisotropic properties are further determined utilizing the logging instrument in a like manner. A sand resistivity and a net/gross ratio may be derived from the formation and shale layer anisotropic information.

Abstract: A sensor protection system for use with an MWD tool includes a tubular body having lesser and greater diameter portions, antennas mounted in grooves in the lesser diameter portion, shield sleeves covering the antennas and being locked in place against longitudinal and rotational movement, and a wear band on the greater diameter portion to provide a standoff for the shield sleeve, the wear band also being locked against movement in the longitudinal and rotational directions. The locking mechanism also can be used to fix a sleeve-type stabilizer on the tubular body.

Abstract: A method of extracting a phase and amplitude modulation signal impressed on a carrier is disclosed. The method includes generating the carrier at a frequency which is a multiple of the bandwidth of the modulation signal. The multiple equals 4N+1, where N is an integer. The modulation signal is impressed on the carrier, generating a phase and amplitude modulated carrier, The modulated carrier is digitally sampled at a frequency of four times the bandwidth the modulation signal. The digital sampling is initiated substantially contemporaneous with initiation of generating the carrier. A 90-degree phase shift is applied to the digitally sampled carrier to generate a quadrature component of the digitally sampled carrier.

Abstract: An apparatus for determining a property of earth formations surrounding a borehole is presented. In accordance with a particular embodiment, an elongated logging device movable through a borehole is provided with a transmitter array consisting of only first, third, and second transmitting antennas longitudinally spaced on the device. A pair of longitudinally spaced receiving antennas are also provided and are located between the second transmitting antenna and one of the first and third transmitting antennas. In particular, the first, third, and second transmitting antennas are spaced from the midpoint between the receiver pair by first, third, and second distances, respectively, where the first and second distances are substantially the same while being different from the third distance. This antenna arrangement is possible while still providing a borehole compensated output.

Abstract: The present invention is directed to a measurement-while-drilling logging tool which includes a minimum number of analog electrical and electronic components, and which instead utilizes digitally-controlled electronic and electrical components to obtain an accuracy which is not possible utilizing prior art measurement-while-drilling logging tools. Additionally, the present invention allows for calibration operations to be conducted before, during, and after logging operations. Preferably, the calibration operations are performed periodically or intermittently during logging operations, and recorded, to be utilized later in explaining any irregularities in the log data. This calibration operation during drilling operations is not found in prior art devices, and is rendered practical by the utilization of digitally-controlled electrical and electronic components in lieu of analog components which are traditionally utilized in logging tools.

Abstract: A method for detecting and sensing boundaries between strata in a formation during directional drilling so that the drilling operation can be adjusted to maintain the drillstring within a selected stratum is presented. The method comprises the initial drilling of an offset well from which resistivity of the formation with depth is determined. This resistivity information is then modeled to provide a modeled log indicative of the response of a resistivity tool within a selected stratum in a substantially horizontal direction. A directional (e.g., horizontal) well is thereafter drilled wherein resistivity is logged in real time and compared to that of the modeled horizontal resistivity to determine the location of the drill string and thereby the borehole in the substantially horizontal stratum. From this, the direction of drilling can be corrected or adjusted so that the borehole is maintained within the desired stratum.