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.

Well logging apparatus and method with borehole compensation including multiple transmitting antennas asymmetrically disposed about a pair of receiving antennas

An apparatus for determining the resistivity of formations surrounding an earth borehole. An elongated electrically conductive body is movable through the borehole. A first transmitter establishes a first current in the body from a first transmitter position on the body, the first current traveling in a path that includes the body and the formations. An electrode is mounted on the body and has a surface that is electrically isolated from the surface of the body. A first electrical signal, resulting from the first current, is measured at the electrode. A second transmitter establishes a second current in the body from a second transmitter position on the body that is spaced from the first transmitter position, the second current traveling in a path that includes the body and the formations. A second electrical signal, resulting from the second current, is measured at the electrode. A current monitor measures the axial current passing a monitor position on the body to obtain a monitor current value. An indication of formation resistivity is derived as a function of the first electrical signal, the second electrical signal, and the monitor current value.

Apparatus and method for determining the resistivity of earth formations

Methods and systems for creating a numerical pseudocore model, comprising: a) obtaining logging data from a reservoir having depth-defined intervals of the reservoir, and processing the logging data into interpretable borehole image data having unidentified borehole image data; b) examining one of the interpretable borehole image data, other processed logging data or both to generate the unidentified borehole image data, processing the generated unidentified borehole image data into the interpretable borehole image data to generate warped fullbore image data; c) collecting one of a core from the reservoir, the logging data or both and generating a digital core data from one of the collected core, the logging data or both such that generated digital core data represents features of one or more depth-defined interval of the reservoir; and d) processing generated digital core data, interpretable borehole image data or the logging data to generate realizations of the numerical pseudocore model.

Method to generate numerical pseudocores using borehole images, digital rock samples, and multi-point statistics

An apparatus for obtaining resistivity parameters of earth formations (7) uses capacitive coupling (5) for injecting measure currents into the formation through a nonconducting mud. In one embodiment, a modulated electrical current is used. Alternatively, multifrequency measurements may be made to obtain the resistivity parameter. In an optional embodiment, the modulation frequency is in the AF range, making it possible to use prior art circuitry designed to reduce cross talk. Measurements may be made either on a wireline or in a MWD configuration.

An apparatus and method for wellbore resistivity determination and imaging using capacitive coupling

A disclosed embodiment utilizes one or more toroidal coil antennas mounted, in an insulating medium, on a drill collar to induce currents which travel in a path that includes the drill collar and earth formations around the drill collar. At least one array of electrodes is provided on at least one stabilizer blade of the drill collar and is utilized to detect currents transmitted by toroidal coil antennas which return via the formations to the electrodes laterally; that is, approximately normal to the axis of the drill collar. Signal traces are obtained from measurements taken at respective ones of the transducers, and a dip characteristic of the formations is determined from the signal traces and from signals representing the rotational orientation of the drill collar.

Dipmeter apparatus and method using transducer array having longitudinally spaced transducers

Methods and apparatuses for electrically investigating a borehole are described. Tool mounted pads are provided, each with a plurality of small measure electrodes from which individually measurable survey currents are injected toward the wall of the borehole. The measure electrodes are arranged in an array in which the measure electrodes are so placed at intervals along at least a circumferential direction (about the borehole axis) as to inject survey currents into the borehole wall segments which overlap with each other to a predetermined extent as the tool is moved along the borehole. The measure electrodes are made small to enable a detailed electrical investigation over a circumferentially contiguous segment of the borehole so as to obtain indications of the stratigraphy of the formation near the borehole wall as well as fractures and their orientations. In one technique, a spatially closed loop array of measure electrodes is provided around a central electrode with the array used to detect the spatial pattern of electrical energy injected by the central electrode. In another embodiment, a linear array of measure electrodes is provided to inject a flow of current into the formation over a circumferentially effectively contiguous segment of the borehole. Discrete portions of the flow of current are separably measurable so as to obtain a plurality of survey signals representative of the current density from the array and from which a detailed electrical picture of a circumferentially continuous segment of the borehole wall can be derived as the tool is moved along the borehole. In another form of an array of measure electrodes, they are arranged in a closed loop, such as a circle, to enable direct measurements of orientations of resistivity of anomalies.

Method and apparatus using pad carrying electrodes for electrically investigating a borehole

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.

Method and apparatus for producing an image log of a wall of a borehole penetrating an earth formation

A high resolution method and apparatus for measuring the depth of a tool suspended from a cable inside a borehole are described. The tool includes accelerometers for measuring its acceleration and this measurement is combined with a cable depth measurement with which the amount of cable in the borehole is determined. A Kalman filter is employed to continually provide estimates of the velocity and depth of the tool from the accelerometer and cable depth measurements. A filter modifier alters operation of the filter during discontinuous motions of the tool such as when it is stuck and slips. A tool sticking detector senses when the tool is stuck and for how long to correspondingly modify the filter by forcing it to more strongly rely upon accelerometer measurements when the tool is stuck and gradually return to normal filter operation when the tool resumes movement after having been stuck.

Method and apparatus for measuring the depth of a tool in a borehole

0 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.

Method and apparatus for producing an image log of a borehole wall penetrating an earth formation

Methods and apparatus, for processing signals derived along portions of the length of a borehole to determine the relative position of geological formation characteristics, effect the correlation of pairs of signals using substantially overlapping correlation intervals to obtain cross-correlation functions for each pair of signals. These cross-correlation functions are then displayed as a function of borehole depth for each pair of curves such that discontinuities in the cross-correlation functions are rendered obvious. From such discontinuities, zoning of the data is enabled through determination of the position of significant continuous intervals. Sequences of cross-correlation functions which belong to one of these intervals may then be used to directly determine the corresponding relative position of a formation characteristic. When applied to dipmeter signals, the method produces more accurate and geologically consistent dip and azimuth values for subsurface formations.

Chan David So Keung

Papers

Method and apparatus using pad carrying electrodes for electrically investigating a borehole

Method and apparatus for producing an image log of a wall of a borehole penetrating an earth formation

Method and apparatus for measuring the depth of a tool in a borehole

Method and apparatus for producing an image log of a borehole wall penetrating an earth formation

Dipmeter data processing technique