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. This invention also relates to a method and apparatus for steering a downhole tool during a drilling operation in order to maintain the borehole within a desired earth formation. The steering capability is enabled by computing the difference or the ratio of the phase-based or amplitude-based responses of the receiver antennas which are mounted in planes that are not parallel to the planes of the transmitter antennas. Although this invention is primarily intended for MWD or LWD applications, this invention is also applicable to wireline and possibly other applications.

Electromagnetic wave resistivity tool having a tilted antenna for geosteering within a desired payzone

The short hop communication link includes a sensor module (125) positioned downhole from a motor (100) in a well. The module (125) includes sensors that monitor operational, directional and environmental parameters downhole and provide an electrical data signal indicative thereof. Sensors may also be positioned in the drill bit (50) for obtaining parameters related to the bit, and communicating data signals reflecting the sensed parameters to the sensor module (125). The sensor module (125) includes a transceiver, with an annular antenna (25), for transmitting electromagnetic sensor data signals to a point above the motor (100). A control module (40), which also includes a transceiver with an annular antenna (37), is located above the motor (100), and receives the electromagnetic signals from the sensor module (125) reflecting the sensed parameters. In addition, the control module (40) is capable of transmitting command signals to the sensor module (125) requesting data regarding desired parameters. The command module (40) connects to a host module (10) which orchestrates all measurement-while-drilling components downhole. The host module (10) connects to a mud pulser (35) for transmitting desired data to the surface for real-time processing. The sensor module (125) is strategically placed within a removable, interchangeable sub (200) below the motor (100), or alternatively, within an extended driveshaft (400) of the motor (100), while the sensor antenna (25) is located on an exterior shoulder of the sub (200) or driveshaft (400). The sensor module (125) and an associated battery pack (55) reside within a pressure container (99) which forms pan of a current return path from the sensor antenna (25) to the circuitry within the sensor module (125).

Short hop communication link for downhole mwd system

A compression and decompression system in which a reversible wavelet filter are used to generates coefficients from input data, such as image data. The reversible wavelet filter is an efficient transform implemented with integer arithmetic that has exact reconstruction. The present invention uses the reversible wavelet filter in a lossless system (or lossy system) in which an embedded codestream is generated from the coefficients produced by the filter. An entropy coder performs entropy coding on the embedded codestream to produce the compressed data stream.

Method and apparatus for compression using reversible wavelet transforms and an embedded codestream

A method and apparatus for determining the distance and direction of a well from a borehole. A toroidal inductor surrounds a drill stem within a borehole. The inductor acts as a primary for a transformer, with the drill stem, the earth surrounding the borehole, and electrically conductive material at the target well forming a single loop transformer secondary. An oscillator is connected to the primary to produce an induced AC current in the secondary. Secondary current flowing in the target well produces an AC secondary magnetic field which is detected at the borehole.

Apparatus for locating an elongated conductive body by electromagnetic measurement while drilling

A compression and decompression method uses a wavelet decompositin, frequency based tree encoding, tree based motion encoding, frequency weighted quantization, Huffman encoding, and/or tree based activity estimation for bit rate control. Forward and inverse quasi-perfect reconstruction transforms are used to generate the wavelet decomposition and to reconstruct data values close to the original data values. The forward and inverse quasi-perfect reconstruction transforms utilize special filters at the boundaries of the data being transformed and/or inverse transformed. Structures and methods are disclosed for traversing wavelet decompositions. Methods are disclosed for increasing software execution speed in the decompression of video. Fixed or variable length tokens are included in a compressed data stream to indicate changes in encoding methods used to generate the compressed data stream.

Data compression and decompression

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.

Method and apparatus for directional well logging with a shield having sloped slots

An electrical induction sonde for measuring a characteristic of an earth formation traversed by a borehole having improved vertical resolution and excellent depth of penetration. The sonde has two or more transmitter-receiver spacings preselected to provide at least two separate induction signals received from the formation that, when combined, produce a response function indicative of formation physical properties with no zeros in the spatial frequency response function over the frequency domain of interest.

Spatial frequency method and apparatus for investigating earth conductivity with high vertical resolution by induction techniques

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. An embodiment of the instrument includes an antenna disposed between a pair of electrically coupled electrodes. The antenna is disposed on the instrument such that it comprises a tilted or transverse magnetic dipole. Another embodiment of the instrument includes a non-conductive housing with a conductive segment disposed thereon. An antenna is disposed on the instrument about the conductive segment. Another embodiment includes an antenna disposed between two pairs of electrodes with means to measure a voltage at the electrodes when electromagnetic energy is transmitted within the borehole. Yet another instrument includes an antenna disposed between a first pair of electrodes and means to measure a voltage at the electrodes when electromagnetic energy is transmitted within the borehole. This embodiment also includes means to energize a second electrode pair in response to the voltage measured at the first electrode pair.

Method and apparatus for cancellation of borehole effects due to a tilted or transverse magnetic dipole

Induction logging sonde including transmitter and receiver solenoid coils mounted on a support and axially separated from each other. The support is made of conductive material and comprises at least one first longitudinal portion for mounting the coils and second longitudinal portions on each side of the first portion. At least the first portion has a substantially continuous and axisymmetric outer surface so as to favor the flow of eddy currents around the surface, whereby the electric field on that surface is substantially cancelled.

Thomas D. Barber

Papers

Method and apparatus for directional well logging with a shield having sloped slots

Spatial frequency method and apparatus for investigating earth conductivity with high vertical resolution by induction techniques

Method and apparatus for cancellation of borehole effects due to a tilted or transverse magnetic dipole

Induction logging sonde with metallic support

Induction logging sonde with metallic support having a coaxial insulating sleeve member