Abstract: A method for magnetizing a wellbore tubular is disclosed. The method includes magnetizing a wellbore tubular at three or more discrete locations on the tubular. In exemplary embodiments the magnetized wellbore tubular includes at least one pair of opposing magnetic poles located between longitudinally opposed ends of the tubular. Wellbore tubulars magnetized in accordance with this invention may be coupled to one another to provide a magnetic profile about a section of a casing string. Passive ranging measurements of the magnetic field about the casing string may be utilized to survey and guide drilling of a twin well. Such an approach advantageously obviates the need for simultaneous access to both wells.

Abstract: A method of estimating standoff in a borehole through an earth formation, includes: disposing a sensor including a plurality of return electrodes and at least one transmitter electrode disposed in a concentric arrangement into the borehole; injecting current, I, into the formation by applying at least two frequencies of alternating current (AC) voltage between at least two of the electrodes; measuring impedance, Z, for each of the frequencies; and using a predetermined relationship between impedance, Z, and standoff, estimating the standoff. A system and a computer program product are provided.

Abstract: An apparatus, method and computer-readable medium for obtaining a resistivity image of an earth formation. The apparatus includes a downhole assembly configured to be conveyed in a borehole penetrating the earth formation; a plurality of sensor electrodes on the downhole assembly, each of the plurality of sensor electrodes having a different capacitance to a wall of the borehole; and at least one processor configured to: (i) process measurements using each of the sensor electrodes; (ii) process a subset of the measurements substantially unaffected by the different capacitances to produce an image of the borehole wall; and (iii) record the image on a suitable medium.

Abstract: Methods and apparatus for determining a presence of a non-conductive coating on electrodes in fluid resistivity measurement devices are described. An example method of determining a presence of a non-conductive coating on electrodes of a fluid resistivity measurement device involves obtaining a first electrical potential value associated with a substantially uncoated condition of first and second electrodes of a fluid resistivity measurement device. The example method also involves measuring a second electrical potential value at a location between the first and second electrodes, comparing the first and second electrical potential values, and determining the presence of a non-conductive coating on at least one of the first and second electrodes based on the comparison.

Abstract: A method for providing a symmetric resistivity image of a formation using at least one asymmetric sensor, includes: collecting a plurality of resistivity images, each of the images collected from the at least one asymmetric sensor disposed on a pad; assembling the plurality of resistivity images about a selected reference point; and processing the plurality of resistivity images to provide a symmetric image of the formation. A computer program product and an instrument are disclosed.

Abstract: Sequential measurements are made using a two terminal resistivity imaging device wherein the measure electrodes are activated sequentially with the remaining electrodes in a floating mode. This eliminates the hardware requirements for focusing electrodes, prevents galvanic leakage between proximal electrodes and the effects of mutual coupling between circuits including proximal electrodes.

Abstract: In some embodiments, apparatus useful for determining at least one dimension of at least one geological feature of an earthen formation from a subterranean well bore includes at least two emitting electrodes and at least one sensing electrode disposed in the well bore. The emitting electrodes are configured to create an electric field and the at least one sensing electrode is configured to detect perturbations in the electric field created by at least one target object.

Abstract: An apparatus for imaging a subsurface material traversed by a borehole, the apparatus including an imaging pad deployed by a logging instrument, the pad including a plurality of measuring sets, each measuring set including a first current injector electrode, a second current injector electrode, a pair of sensor electrodes disposed between the first current injector electrode and the second current injector electrode, and an output for coupling to an electronics unit adapted for producing the imaging of the subsurface material.

Abstract: An apparatus for making azimuthally sensitive resistivity measurements of a subterranean formation is disclosed. The apparatus includes a magnetically permeably ring deployed about an electrically conductive tool body. An AC voltage supply is coupled to the tool body on opposing sides of the magnetically permeable ring, with at least one connecting conductor crossing outside the ring. Exemplary embodiments of this invention may further include one or more current sensing electrodes deployed in and electrically isolated from an outer surface of a blade deployed on the tool body and may be utilized to make azimuthally resolved formation resistivity measurements.

Abstract: An unfocused resistivity imaging device horizontal and vertical currents conveyed into the borehole. Pad mounted electrodes are used to make voltage measurements in orthogonal directions. The voltage measurements are then rotated to give principal resistivity measurements in an anisotropic formation with dipping beds.

Abstract: A combined resistivity tool incorporating both induction/propagation antennas and lateral resistivity antennas disposed in recesses of downhole tubulars, in which a lateral resistivity antenna includes an insulating base layer disposed in the recess; a toroidal antenna disposed over the insulating base layer; and a shield disposed over the recess.

Abstract: A device, method and system for measuring characteristics of a geologic formation using a floating reference signal having a mud chamber, an electrode disposed within the mud chamber, and an electrically conductive plate disposed within the mud chamber, the plate separated from the electrode. An alternating current source is provided on the electrode, whereby an electric field is be maintained between the electrode and the conductive plate. An opening in the mud chamber allows drilling fluids to pass there through.

Abstract: An apparatus used in electrical investigation of geological formations GF surrounding a borehole BH, comprises: an electrically conductive body 102 movable through the borehole BH, at least one first transmitter T1 for inducing a first current from a first transmitter position and traveling in a path that includes a first portion of the body and a selected zone SZ of the geological formations GF, at least one second transmitter T2 for inducing a second current from a second position and traveling in a path that includes a second portion of the body and the selected zone SZ, the second transmitter T2 position being different from the first transmitter T1 position on the body, at least a first M0, second M1 and third M2 axial current sensors for measuring a first, a second and a third axial current flowing along the body, respectively, the first, second and third axial current sensor position on the body being different from each other, and at least one lateral current sensor R2 disposed on the body for meas

Abstract: A sensor electrode for imaging a formation, includes a geometry that one of reduces or substantially limits spatial aliasing in formation data, the aliasing resulting from imaging the formation with an array of the sensor electrodes. A method and a computer program product for designing sensor electrodes are provided. A sensor with a one-row wavelet geometry is disclosed.

Abstract: Logging-while-drilling apparatus and methodologies for measuring streaming potential in an earth formation are provided. The apparatus and methodologies can be utilized to find information relevant to the drilling operations. In particular, since the streaming potential measurement relates directly to fluid flow, the streaming potential measurements can be used to track flow of fluids in the formation. In turn, this information may be used to find information relevant to the drilling operations, such as under-balanced drilling conditions, abnormal formation pressures, open fractures, the permeability of the formation, and formation pressure.

Abstract: A resistivity imaging device injects currents in two orthogonal directions using two pairs of return electrodes and performing impedance measurements of the buttons placed between the returns.

Abstract: Oil-based mud imaging systems and methods that measure formation permittivity. In some embodiments, disclosed logging systems include a logging tool in communication with surface computing facilities. The logging tool is provided with a sensor array having at least two voltage electrodes positioned between at least two current electrodes that create an electric field in a borehole wall, and is further provided with electronics coupled to the voltage electrodes to determine a differential voltage magnitude and phase. From the magnitude and phase, formation resistivity and permittivity measurements can be determined and used to construct a borehole wall image.

Abstract: An apparatus for making azimuthally sensitive resistivity measurements of a subterranean formation is disclosed. The apparatus includes a magnetically permeably ring deployed about an electrically conductive tool body. An AC voltage supply is coupled to the tool body on opposing sides of the magnetically permeable ring, with at least one connecting conductor crossing outside the ring. Exemplary embodiments of this invention may further include one or more current sensing electrodes deployed in and electrically isolated from an outer surface of the tool body and may be utilized to make azimuthally resolved formation resistivity measurements.

Abstract: A logging tool used in a borehole having non-conductive mud. The tool includes a known inductance in series with an electrode. The quality factor of a circuit that includes the electrode, the inductance and the earth formation is indicative of the resistivity of the formation. The quality factor may be determined using either a plurality of signals or by measuring a transient response.

Abstract: An instrument is disclosed for measuring resistivity of Earth formations from within a conductive pipe inside a wellbore drilled through the formations. The instrument includes a plurality of housings connected end to end and adapted to traverse the wellbore. At least one electrode is disposed on each housing. Each electrode is adapted to be placed in electrical contact with the inside of the pipe. The instrument includes a source of electrical current, a digital voltage measuring circuit and a switch. The switch is arranged to connect the source of electrical current between one of the electrodes and a current return at a selectable one of the top of the pipe and a location near the Earth's surface at a selected distance from the top of the pipe, and to connect selected pairs of the electrodes to the digital voltage measuring circuit. The pairs are selected to make voltage measurements corresponding to selected axial distances and selected lateral depths in the Earth formations.

Abstract: A probe 1 for measuring the electromagnetic properties of a down-hole material MC, GF, DM of a well-bore WB comprises a metallic pad 2 in contact with the down-hole material. The pad 2 further comprises an open-ended coaxial wire 4 coupled to an electronic circuit 3. The open-ended coaxial wire 4 comprises an inner conductor 4A sunk in an insulator 4B and is positioned sensibly perpendicularly to the well-bore wall. The electronic circuit 3 is able to send a high-frequency input signal into the open-ended coaxial wire 4 and to determine a reflection coefficient based on a high-frequency output signal reflected by the open-ended coaxial wire 4.

Abstract: A resistivity imaging tool determines formation resistivity by evaluating the resonant frequency and the quality factor of a resonant circuit associated with a current electrode. A planar coil electrode may be used to provide the necessary inductance and capacitance for the resonant circuit.

Abstract: The invention concerns a method for determining the position, in a formation (1) containing at least one electrolytic liquid, of an interface (6) in relation to a bore hole (2). One stimulates at a first instant the interface (6) with an excitation signal, one detects at a second instant (t2) a response signal converted by electro-osmosis or electrokinetic coupling effect and, if appropriate, the exication signal after reflection at a third instant (t3). With the three instants and the propagation velocity of the signals, one calculates the distance between the interface (6) and the bore hole (2).

Abstract: A method is disclosed for determining spatial distribution of resistivity of Earth formations surrounding a wellbore having a conductive pipe therein. The method includes measuring resistivity of the Earth formations using measurements of current leakage along the pipe at selected axial positions. Electromagnetic properties of the Earth formations are measured from within the pipe. The measurements of electromagnetic properties correspond to a larger axial distance and to a greater lateral distance than the measurements of resistivity from current leakage. The current leakage and electromagnetic measurements are jointly inverted to obtain a model of the spatial distribution.

Abstract: A porous geological formation contains electrolytic fluid. During the geophysical prospecting of the formation, a region of interest of the formation where the electrolytic fluid is found is stimulated with an excitation signal. The excitation signal corresponds to an energy of a first type. The excitation signal is converted in the region of interest into a response signal. The response signal corresponds to an energy of a second type. The response signal is detected. An electric polarisation is applied to the region of interest so as to strengthen the response signal relative to what it would be in the absence of polarisation. The electric polarisation comes about by means of a continuous or quasi-continuous polarising electric field. The polarising electric field is modulated in frequency with a frequency which is low relatively to the excitation frequency.

Abstract: A method and apparatus for minimizing direct coupling between transmitters and receivers on a downhole logging tool are disclosed. One embodiment includes a transmitter, a bucking device, and a plurality of receivers, where signals may be directly coupled from the transmitter into the receivers and signals may be indirectly coupled from the transmitter into the receivers through the formation and borehole environment. The bucking device minimizes the magnitude of the signals that are directly coupled from the transmitter into multiple receivers within the plurality. By varying the current in the bucking device, the bucking device minimizes the magnitude of the directly coupled signal of each receiver in the plurality, and each receiver may utilize a common bucking device.

Abstract: The invention provides an apparatus for making an electromagnetic measurement from within a subsurface borehole. The apparatus comprises an elongated support having electrically conductive segments and adapted for disposal within the borehole; an antenna adapted to transmit electromagnetic energy disposed on the support such that its axis is tilted or perpendicular with respect to the axis of the support; a sensor disposed on the support and adapted to detect a current flow along the support when the antenna is activated to transmit electromagnetic energy; and means to process the detected current flow to provide an indication of the measurement quality or the position of the support within the borehole.

Abstract: The invention relates to a device for measuring an electrical parameter through electrically-conductive casing, said device including a current injection electrode (3) and a measurement electrode (7) on one side of the wall of the casing (1). According to the invention, the injection electrode (3) is associated via a first magnetic coupler (4) with a current source (2) and the measurement electrode (7) is associated via a second magnetic coupler (6) with a measurement device (5) situated on the other side of the wall.

Abstract: Methods and apparatus for detecting and monitoring the borehole effect in subsurface measurements. Toroidal sensor configurations address the undesired axial electric currents that travel along the borehole when antennas with tilted or transverse axes are used to make electromagnetic measurements. Embodiments use currents measured along the instrument to determine the quality of measured logs, the borehole size, and instrument position or orientation within the borehole.

Abstract: An apparatus for obtaining resistivity images of a borehole includes an array of measure electrodes separated from a pad or the body of the instrument by a focusing electrode. The focusing electrode is maintained at a slightly higher potential than the measure electrodes. The apparatus is primarily intended for use with conducting fluids but may also be used with non-conducting fluids. A modulated electrical current with a carrier frequency of 1 MHz is injected into the formation. When used with a non-conducting fluid, capacitive coupling between the electrode and the conductive formation is provided by the dielectric of fluid. When used with a conducting borehole fluid, an additional capacitor may be incorporated into the circuit. The current in the measure electrode is indicative of the conductivity of the formation.

Abstract: A downhole electrical power system provides long term electrical power in a downhole environment. In a described embodiment, a downhole electrical power system includes a power source which supplies electrical power to a well tool interconnected in a tubular string. The power source includes a voltaic cell.

Abstract: In an electrical measurement apparatus and method for measuring an electrical characteristic of an earth formation, such as in a hole drilled for the exploration for hydrocarbons, a detection portion has an operational amplifier operating in voltage follower mode, with a measurement resistor in the feedback loop. The detection portion will typically include a plurality of sensor elements, and the operational amplifier can be switched between the sensor elements. The apparatus also includes a measurement portion adapted to measure the current flow through the measurement resistor, the calculation portion including an integrator.

Abstract: A miniaturized electrical resistivity (ER) probe based on a known current-voltage (I-V) electrode structure, the Wenner array, is designed for local (point) measurement. A pair of voltage measuring electrodes are positioned between a pair of current carrying electrodes. The electrodes are typically about 1 cm long, separated by 1 cm, so the probe is only about 1 inch long. The electrodes are mounted to a rigid tube with electrical wires in the tube and a sand bag may be placed around the electrodes to protect the electrodes. The probes can be positioned in a borehole or on the surface. The electrodes make contact with the surrounding medium. In a dual mode system, individual probes of a plurality of spaced probes can be used to measure local resistance, i.e. point measurements, but the system can select different probes to make interval measurements between probes and between boreholes.

Abstract: A petroleum well (20) for producing petroleum products that incorporates a system adapted to controllably measure a formation resistivity using induction chokes (91-95) to form electrically isolated piping structure sections that can be used as the formation contact electrodes for time-varying current, and methods of producing petroleum products while measuring formation resistivity, are provided by the present invention. The system comprises a first induction choke (91), a second induction choke (92), and a device (50). The first induction choke (91) is located about a piping structure (30) of the well (20). The second induction choke (92) is also located about the piping structure (30) of the well (20), but the first induction choke (91) is distally spaced from the second induction choke (92). The device (50) is located outside of the piping structure (30) and comprises two terminals (71, 72).

Abstract: Methods and apparatus are disclosed for minimizing or eliminating an undesired axial electric current induced along a subsurface borehole in the process of subsurface measurements with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Some antennas are disposed within the borehole on instruments having a non-conductive support member. One instrument includes a conductive all-metal body with an antenna adapted for induction frequencies. Antenna shields adapted for controlled current flow are also provided with an all-metal instrument. Methods include providing an alternate path for the current along the instrument body. Another method includes emitting a controlled current to counter the undesired current. Another method corrects for the effect of the current using a superposition technique.

Abstract: A method and apparatus for navigating a tool string down a subsurface borehole to its intended location while simultaneously measuring or sensing the borehole environment, electrically, acoustically, mechanically, or by nuclear means, for a characteristic parameter. The hole-finder apparatus incorporating a locally flexible body adapted for attachment to the tool string. As the tool string is navigated through the borehole, the flexible body provides extreme local flexibility to lessen the likelihood of jamming the tool string while tripping down the borehole by providing a lateral force at the obstruction. The hole-finder apparatus further including a sensor or probe measuring means attached to or within the tip of the flexible body for measuring the characteristic parameter.

Abstract: Inception of hydrocarbon extraction from a reservoir causes the oil-water interface to warp and cusp toward the extraction gates along a well. This invention proposes time-lapse DC/AC measurements with an array of permanently deployed sensors in order to detect and estimate the change in geometry and proximity of the oil-water interface as a result of production, and therefore as a function of time. The estimation is carried out with a parametric inversion technique whereby the shape of the oil-water interface is assumed to take the form of a three-dimensional surface describable with only a few unknown parameters. A nonlinear optimization technique is used to search for the unknown parameters such that the differences between the measured data and the numerically simulated data are minimized in a least-squares fashion with concomitant hard bound physical constraints on the unknowns.

Abstract: A logging apparatus is adapted to be disposed in a mud filled wellbore, and a measurement probe is connected to a bottom of a tool string of the logging apparatus. The measurement probe is adapted for measuring a resistivity of a mud in the mud filled wellbore. The measurement probe includes a bottom electrode disposed on a bottom of the probe when the logging apparatus is disposed in the wellbore, a second electrode, and at least one measurement electrode disposed adjacent the bottom electrode for measuring a voltage potential drop in a region of the mud which is disposed directly below the bottom electrode of the measurement probe when the probe is disposed in the wellbore. When the measurement probe is energized, a current flows in the mud between the bottom electrode and the second electrode.

Abstract: A method for concurrently gathering acoustic and resistivity data for mapping the texture of the sidewall of a borehole using a single imaging tool. The data are sampled, formatted and merged to provide a single composite image of the borehole sidewall.

Abstract: A method of interpretation of electrical dispersion data relating to porous media such as soil, the media having a solid phase and a fluid phase, includes the steps of electromagnetically taking, as a function of megahertz frequency, a plurality of bulk material measurements of the parameters of conductivity and dielectric constant. The method further includes the step of inputting said conductivity and dielectric data into dispersion functions having, as their solvable variables, parameters including at least solid phase conductivity and dielectric constant, fluid phase conductivity and dielectric constant, and solid-fluid phase interface conductivity and dielectric constant. Information may also be obtained with respect to the parameters of particle shape, particle size, particle orientation, porosity, water content, and non-water content.

Abstract: An electrode for use in the electrical investigation of a medium such as a borehole wall, comprises a sheet (32) of electrically resistive material having opposed first (34) and second (33) surfaces, one or more elongate electrical conductors (35,36) of low resistivity, an end face of each conductor abutting the first surface of the sheet (32) and means for sensing electric current passing through each conductor. In use, the second surface (33) of the sheet (32) is exposed to the medium to be investigated.

Abstract: A rigid bridle for supporting a current emitting logging tool in a sonde is set forth. The rigid bridle is formed of multiple segments of tubular members, normally formed of metal. At selected locations along the length thereof, they are interrupted by electrical insulators which prevent current flow along the length thereof. Moreover, the external surface is coated with first one and then the second layer of insulative material; three such units in serial assembly support a return current electrode for use in a current emitting logging tool. In an alternate form, a short electrical isolator joint is set forth which includes concentric metal members which are spaced from one another when assembled by insulative members positioned therebetween so that current flow along the length thereof is prevented.

Abstract: A method of determining parameters of a geological environment having a known electrical resistivity R.sub.h, with a heterogeneity in the environment having an electrical resistivity R.sub.e, and with a borehole extending into either the environment or the heterogeneity at an unknown distance p from the interface between the environment and the heterogeneity. A measuring assembly is extended into the borehole, including an electrical emitter and two or more electrical detectors. Electrical energy is applied to the emitter and detected by one of the detectors at a distance d from the emitter, and the borehole resistivity R.sub.a at the distance d is determined. This is repeated for others of the detectors at other distances d. A curve is plotted of the resistivity ratio R.sub.a /R.sub.h as a function of the distance d. The plotted curve is compared with previously obtained curves of the resistivity ratio R.sub.a /R.sub.h as a function of d for various combinations of the values of the resistivity ratio R.sub.

Abstract: The logging tool comprises a gas void fraction measurement section (37) consisting of a first set (37) of eight longitudinal electrodes (38) extending parallel to the longitudinal axis of the tool and positioned and regularly spaced around said longitudinal axis, a sleeve (40) made of dielectric material and located in contact and around the electrodes for obtaining an electric field pattern distributed essentially radially between the electrodes and the wall (12) of the borehole facing the electrodes (38), a centralizer (32) for substantially centralizing the tool in the borehole, and a circuit means (69-115) for measuring sequentially the capacitance between two adjacent electrodes for each pair of electrodes, said capacitance being characteristic of the gas void fraction of the fluid flowing in the wellbore. The logging tool comprises in addition a cross correlation gas velocity measurement section (28) which includes a second (48) and a third (50) set of electrodes.

Abstract: An articulated downhole surveying instrument and method for measuring parameters of a wellbore includes one or more laterally flexible coupling sections. The laterally flexible coupling sections are rigid in axial tension and axial compression, and are smaller in cross-section than the surveying instrument housing. A separate housing is used for each component of the surveying instrument, and each component housing is interconnected with the laterally flexible coupling. One or more flexible spacer bars are also provided. The spacer bars and coupling sections enable the assembly to be passed through a short-radius angle wellbore with greatly reduced risk of sticking or hanging up.

Abstract: A method and apparatus for investigating earth formations surrounding a borehole operates by selectively heating a region of the formations, and measuring the thermal response to obtain useful information concerning the characteristic length scales of the pores in the heated region. The thermal response is obtained indirectly by measuring the electrical conductivity response. The invention can be utilized to obtain, inter alia, indications of porosity, permeability, and the distribution of pore geometries. In accordance with an embodiment of the method of the invention, the following steps are performed: heating a region of the formations with a series of pulses of microwave electromagnetic energy; measuring the conductivity characteristic of the region which result from the heating pulses; and determining a property of the region of the formations from the measured conductivity characteristic.

Abstract: A tool with a switch is inserted and moved down the inside of tubular-shaped and electrically conductive casing in the well. Spaced apart contacts on the tool are connected between upper and lower electrically conductive casings located on opposite sides of a high impedance separation in the casing. The switch is operated for creating a changing electrical conductance between the upper and lower casings representative of data. The electrical conductance across the high impedance separation is interrogated with an alternating current signal to retrieve the data.

Abstract: An acoustic method and apparatus for investigating an earth formation penetrated by a borehole are described. Acoustic transducers are mounted on a tool to accurately determine the distance between a segment of the tool and the wall of the borehole. The acoustic transducers are positioned in such manner that the stand-off distance between individual resistivity measuring electrodes in an array, which is also mounted on the tool segment, and the borehole wall can be measured. The stand-off measurement is recorded and may be used to correct the electrode resistivity measurements. In one embodiment a calibration of acoustic transducers as a function of depth is obtained by employing acoustic calibrating transducers to compensate for borehole environment effects on the performance of the acoustic transducers as well as determine the acoustic velocity of the borehole fluid, such as mud. Several embodiments are described.

Abstract: A tool changes the electrical conductance across a nonconductive separation in a string of electrically conductive casing in a well located in the earth. The tool is for transmission of data up the well. The casing has at least one inwardly extending landing shoulder for the tool. The tool has a housing elongated between first and second ends. The housing has a first contact for electrical connection to the casing on one side of the nonconductive separation. The housing has a second contact spaced from the first contact for electrical connection to the casing on the other side of the nonconductive separation from the one side. The housing also has a nonconductive housing portion, substantially circular in cross-section, between the first and second contacts. An outwardly extending landing shoulder is provided on the housing for landing and for supporting the tool on the casing landing shoulder.

Abstract: A technique is described for producing an image log of an investigation of the wall of a borehole with a high resolution tool. The tool employs sensors for measuring a characteristic such as the conductivity of the wall at locations which circumferentially overlap. An accurate tool depth measuring device is employed to modify the measured characteristic so that the measurement can be displayed as a linear function of depth without visually detectable artifacts. Various signal processing and image enhancing techniques are described to produce an image log on which the characteristic can be seen as a variable intensity image in which small scale variations of the measured characteristic remain discernable and significant features visually stand out from the log.