Abstract: Methods and apparatus facilitating measurement of anisotropy are disclosed. According to some aspects, anisotropy can be determined while drilling. Monopole/quadrupole interactions, as well as monitoring dipole excitations and other methods, may be used to find the principal shear directions of a formation while drilling or during wireline or other operations.

Abstract: A tool generates signals indicative a shear wave slowness of the formation surrounding a borehole. The tool comprises a collar portion adapted for mounting in a drill string, a quadrupole sonic transmitter mounted to the collar portion, and a quadrupole sonic receiver array mounted to the collar spaced apart from the transmitter. A method determines shear wave slowness of the formation. The method includes propagating quadrupole wave energy into the formation and detecting quadrupole dispersive waveform received at a second location. Formation shear wave slowness is calculated using dispersive slowness time coherence processing.

Abstract: Methods and apparatus facilitating radial profiling of shear slowness are disclosed. According to some aspects of the invention, acoustic tool bias is accounted for in the calculation of radial profiles. According so some aspects, acoustic tool bias is accounted for by replacing acoustic tool structure with a resonance-impedance model. The resonance-impedance modeling according to principles of the present invention is applicable to vertical, deviated, and horizontal boreholes.

Abstract: Methods and apparatus facilitating radial profiling of shear slowness or shear modulus c66 in the cross-sectional plane of a borehole in an anisotropic formation with the vertical X3-axis are disclosed. According to some aspects of the invention, sonic tool bias is accounted for and removed from radial profiles. According to some aspects, sonic tool bias is accounted for by modeling the sonic tool as a heavy-fluid.

Abstract: A technique for processing acoustic waveforms includes: (a) transforming at least a portion of the acoustic waveforms to produce frequency-domain signals; (b) obtaining a model dispersion curve based on a borehole-formation model having a set of borehole-formation parameters; (c) adjusting phases of the frequency-domain signals according to the model dispersion curve to produce back-propagated signals; (d) computing coherence of the back-propagated signals; (e) repeating steps (b)-(d) by varying values of the set of borehole-formation parameters until the coherence reaches a selected criterion; and (f) outputting at least a portion of the set of borehole-formation parameters.

Abstract: A method for processing acoustic data comprising applying a dynamic filter band. The method and apparatus may be particularly adapted to processing sonic data to measure formation slowness in a borehole.

Abstract: An acoustic logging tool sleeve with a preferably discontinuous, alternating structure that is acoustically opaque in some zones, and acoustically transparent in others. The sleeve may be modular, with several stages connected together. The multiple stages provide a sleeve that may be useful with a variety of borehole logging tools to reduce or eliminate the transmission of noise to the receiving elements.

Abstract: An acoustic logging tool includes external baffle assemblies forming a waveguide structure at the acoustic source. The logging tool is designed for acoustic logging of earth formation surrounding a borehole. The external baffle assemblies form a waveguide structure that is designed to increase signal to noise ratio in an acoustic logging tool using dipole or other acoustic waves. In a preferred embodiment, the acoustic logging tool includes an elongated transmitter module, and a receiver sonde having a linear array of acoustic receivers. The transmitter module includes first and second cylindrical masses spaced apart along the axis by first and second spacers. The first cylindrical mass defines a first circular facing surface and a first cylindrical outer surface. The second cylindrical mass defines a second circular facing surface and a second cylindrical outer surface.

Abstract: A tool generates signals indicative a shear wave slowness of the formation surrounding a borehole. The tool comprises a collar portion adapted for mounting in a drill string, a quadrupole sonic transmitter mounted to the collar portion, and a quadrupole sonic receiver array mounted to the collar spaced apart from the transmitter. A method determines shear wave slowness of the formation. The method includes propagating quadrupole wave energy into the formation and detecting quadrupole dispersive waveform received at a second location. Formation shear wave slowness is calculated using dispersive slowness time coherence processing.

Abstract: A sleeve for an acoustic logging tool has a structure with a window section having fewer bars than a conventional sleeve separated by a slotted region with thin circumferential slots which are stress-relieved at the ends (“dumb-bell” shaped). Steel receiver mounts are provided for hydrophone pressure sensors and this, together with the axially oriented hydrophones makes the tool less susceptible to interfering vibration.

Abstract: An acoustic logging tool includes external baffle assemblies forming a waveguide structure at the acoustic source. The logging tool is designed for acoustic logging of earth formation surrounding a borehole. The external baffle assemblies form a waveguide structure that is designed to increase signal to noise ratio in an acoustic logging tool using dipole or other acoustic waves. In a preferred embodiment, the acoustic logging tool includes an elongated transmitter module, and a receiver sonde having a linear array of acoustic receivers. The transmitter module includes first and second cylindrical masses spaced apart along the axis by first and second spacers. The first cylindrical mass defines a first circular facing surface and a first cylindrical outer surface. The second cylindrical mass defines a second circular facing surface and a second cylindrical outer surface.

Abstract: A sonic logging tool that can be positioned within a fluid-filled borehole includes an axially distributed active vibration control system to reduce tool borne noise. The tool includes an acoustic transmitter, an axial array of acoustic receivers, and actuator assemblies that are coupled to cancel tool mode vibrations at stations along the receiver section of the tool. In a preferred embodiment, force is applied in feedback mode based on tool mode vibrations sensed at each station. The force at each station is applied by a real-time computational algorithm using feedback. The feedback includes weighting to accommodate monopole or dipole tool mode vibration. The computational algorithm includes FIR processing of signals received from a vibration sensor assembly. The force applied at a given station is a function of tool mode vibration measured at that station and the predetermined values of a set of FIR filter coefficients associated with the given station.

Abstract: In one aspect, the invention involves an acoustic logging tool for performing acoustic investigations of subsurface geological formations. In one embodiment, the tool comprises a generally longitudinally extending tool body adapted for positioning in a borehole. At least one transmitter is mounted on the tool body to emit acoustic energy. At least one receiver is also mounted on the tool body at a location axially displaced from the at least one transmitter. The receiver is adapted to receive acoustic energy. An attenuator is also positioned along the body and includes at least one cavity having a plurality of particles disposed therein. The attenuator as disclosed herein may be applied to other logging tools for protecting tool components and enhancing measurement quality. Methods for attenuating acoustic energy transmitted through the body of an acoustic logging tool or other logging tools are also disclosed.

Abstract: A tool generates signals indicative of shear wave slowness of the formation surrounding a borehole. The tool comprises a collar portion adapted for mounting in a drill string, a quadrupole sonic transmitter mounted to the collar portion, and a quadrupole sonic receiver array mounted to the collar spaced apart from the transmitter. A method determines shear wave slowness of the formation. The method includes propagating quadrupole wave energy into the formation and detecting quadrupole dispersive waveforms received at a second location.

Abstract: A tool generates signals indicative of shear wave slowness of the formation surrounding a borehole. The tool comprises a collar portion adapted for mounting in a drill string, a quadrupole sonic transmitter mounted to the collar portion, and a quadrupole sonic receiver array mounted to the collar spaced apart from the transmitter.

Abstract: A sleeve for an acoustic logging tool has a structure with a window section having fewer bars than a conventional sleeve separated by a slotted region with thin circumferential slots which are stress-relieved at the ends (“dumb-bell” shaped). Steel receiver mounts are provided for hydrophone pressure sensors and this, together with the axially oriented hydrophones makes the tool less susceptible to interfering vibration.

Abstract: A sleeve for an acoustic logging tool having a structure with a window section having fewer bars than a conventional sleeve separated by a slotted region with thin circumferential slots which are stress-relieved at the ends (“dumb-bell” shaped). Steel receiver mounts are provided for hydrophone pressure sensors and this, together with the axially oriented hydrophones, makes the tool less susceptible to interfering vibration.

Abstract: A logging tool having a tool body, which can be positioned in a fluid-filled borehole, including a receiver section and a dipole transmitter; wherein the dipole transmitter includes a transducer with a shell having a reaction mass and a motor located therein, the motor operatively connecting the shell and the reaction mass such that only an outer surface of the shell is in contact with the fluid in the borehole. This new type of dipole source for well logging involves shaking all or part (axially) of a dipole tool body to produce a pure, broadband acoustic dipole signal while at the same time coupling as little energy as possible into the tool body. Important variations on this idea include a linear phased array of shaker sources, and active cancellation of tool borne noise.

Abstract: A method, useful in computer-aided design, of identifying possible solutions to an over-constrained system having a collection of entities and constraints. The method represents the entities in terms of degrees of freedom and incrementally assembles the system by adding entities, satisfying constraints and reducing the degrees of freedom of the entities. For an over-constrained system, the method constructs a dependency graph of the system and identifies the set of constraints which over-constrains the system. The over-constraining set includes the constraint which initiated the over-constraint and those constraints back traced in the dependency graph from the initiating constraint. Removal of one or more constraints from the over-constraining set results in a solvable fully or under-constrained system. Intelligent selection of the removed constraint may increase computational efficiency or system stability.

Abstract: A method, useful in computer-aided design, for finding possible configurations of a system having a collection of geometric entities and constraints. The method represents the geometric entities in terms of degrees of freedom and systematically satisfies the constraints reducing the degrees of freedom of the geometric entities. The method uses a number of specialized routines, called plan fragments, which satisfy a particular constraint relating to a particular geometric entity. Each plan fragment changes the configuration of a geometric entity in space--i.e. the location and orientation--satisfying a constraint and reducing a degree of freedom. The series of plan fragments which reduce the degrees of freedom and satisfy the constraints comprise an assembly plan for possible configurations of the system. The method identifies overconstrained, fully constrained, and underconstrained systems to the user and assists in finding possible configurations if the constraints are changed, added, or deleted.