Abstract: The present disclosure belongs to the field of geological exploration, and particularly relates to a seismic acquisition system and a sensor based on an MEMS sensor with low power consumption, so as to solve the problem that the existing seismic wave acquisition technology cannot balance high accuracy and low power consumption when the MEMS sensor is used. The present disclosure comprises: the MEMS sensor is used for receiving seismic wave signals and outputting MEMS sensor electrical signals; a common-mode voltage adjustment module is used for adjusting the MEMS sensor signals to be within the input range of common-mode voltage of a readout circuit, so as to obtain low voltage MEMS sensor signals. In the present disclosure, high voltage ensures the detection accuracy of the MEMS sensor; and low voltage is supplied to the readout circuit, thereby reducing the power consumption of the overall seismic acquisition system.

Abstract: Disclosed are systems and methods for high precision acoustic logging processing for compressional and shear slowness. The method comprises measuring, by a sonic logging tool, sonic data associated with a formation within a borehole, attempting a detection of a first arrival within the sonic data determining whether the attempted detection of the first arrival is accurate, and in response to an accurate detection of the first arrival determining a travel time of the first arrival, generating a coherence map including the first arrival, and determining, based on the coherence map, a characteristic of the formation.

Abstract: The invention relates to petroleum seismic exploration, and more specifically to a method for gas-bearing reservoir characterization using logging information. In the method, logging information is used as a constraint to indirectly characterize the distribution range of the gas-bearing reservoir by determining the upper and lower boundaries. In addition, this method enables the automatic determination of the optimal calculation parameters according to the characteristics of input data, allowing for more accurate results.

Abstract: A method and apparatus for measuring parameters of a borehole using an acoustic logging system. By transmitting a high frequency acoustic signal essentially perpendicular to the major axis of a borehole casing using a transducer, the high frequency acoustic signal may produce one or more acoustic echoes. By receiving and analyzing a first acoustic echo from an inner wall of the borehole casing and at least one second acoustic echo from a back wall of the borehole casing, borehole parameters such as the impedance of the casing cement and the thickness of thicker borehole casings, up to and greater than 1 inch, may be determined.

Abstract: The present disclosure is related to a velocity model update with a full waveform inversion gradient. At least one method can include updating a velocity model of a subsurface, which can include suppressing high wavenumber components of the velocity model provided by reflected energy with a decomposed full waveform inversion gradient. Low wavenumber components can be preserved in the velocity model.

Abstract: Systems and methods which determine geologic properties using acoustic analysis are shown. Acoustic signals are collected during processing (e.g., crushing, shearing, striking, compressing, etc.) of geologic media, such as rock samples, for determining geologic properties according to embodiments. The acoustic signals collected may include frequency information, amplitude information, time information, etc. which may be utilized in determining geologic properties, such as geologic media properties (e.g., mineralogy, porosity, permeability, sealing capacity, fracability, compressive strength, compressibility, Poisson's Ratio, Youngs Modulus, Bulk Modulus, Shear Modulus), geologic structure properties (e.g., lithology, seal quality, reservoir quality), geologic acoustic properties (e.g., acoustic logging effectiveness, acoustic response, natural or harmonic frequencies, etc.).

Abstract: Apparatus and methods are provided. An ultrasonic tool with an array of axially spaced receivers and a transmitter is located in a borehole and is activated. Ultrasonic waveform indications recorded by the receivers are processed and analyzed to determine the presence of non-dispersive headwave signatures. If a non-dispersive headwave signature is located, the presence of a solid such as cement in the annulus is confirmed, and one or more of the compressional and shear velocities of the cement can be determined. If only casing dispersive mode signatures are found, the annulus is determined to possibly contain no cement at the location of interest and additional processing is required.

Abstract: A method for determining properties of a formation comprises disposing at least one acoustic logging tool in a well and moving the logging tool along the well. An acoustic logging is performed during movement of the acoustic logging tool together with simultaneous thermal treatment of the formation. A temperature of a formation zone being thermally treated is measured as well as attenuation and velocity of the Stoneley waves excited by the acoustic logging tool. Based on the obtained dependencies of measured parameters as functions of the formation zone temperature formation relative phase permeabilities, formation fluid viscosity and viscous flow activation energy are determined.

Abstract: An apparatus for use in a wellbore is provided that in one embodiment may include at least one transmitter configured to generate acoustic signals in the wellbore, at least one receiver configured to receive acoustic signals from a formation surrounding the wellbore in response to the transmitted acoustic signal and also configured to provide electrical signals representative of the received acoustic signals, a circuit configured to apply a time-variable gain to the electrical signals to amplify the electrical signals, and a processor configured to process the amplified electrical signals and provide a property of interest.

Abstract: A method for measuring three-dimensional coordinates of a probe center includes: providing a spherically mounted retroreflector; providing a probe assembly; providing an orientation sensor; providing a coordinate measurement device; placing the spherically mounted retroreflector on the probe head; directing the first beam of light from the coordinate measurement device to the spherically mounted retroreflector; measuring the first distance; measuring the first angle of rotation; measuring the second angle of rotation; measuring the three orientational degrees of freedom based at least in part on information provided by the orientation sensor; calculating the three-dimensional coordinates of the probe center based at least in part on the first distance, the first angle of rotation, the second angle of rotation, and the three orientational degrees of freedom; and storing the three-dimensional coordinates of the probe center.

Abstract: Embodiments of this invention relate to compositions and methods of processing a subterranean formation including collecting microseismic data from one wellbore, collecting amplitude ratio information for the microseismic data, comparing the amplitude ratio to an expected ratio, generating a representation of a formation based on the microseismic data and the comparison of the amplitude ratio and expected ratio, and performing an oil field services activity based on the representation.

Abstract: A method and apparatus for correcting an input seismic trace. The method includes receiving the input seismic trace and creating a t by Q gather using the input seismic trace, where t represents traveltime, Q represents absorption parameter, and the t by Q gather has traveltime as the vertical axis and a ratio of t and Q as the horizontal axis. The ratio of t and Q is referred to as R. The method further includes applying an interpolation algorithm to the t by Q gather to derive a corrected input seismic trace.

Abstract: A microseismic monitoring system includes a seismic sensor positioned proximate to a wellbore traversing a formation; an orientation source producing an orientation shot; a hydraulic apparatus operationally connected with the formation to produce a fracture in the formation; a computer control system operationally connected with a database of known spectral attributes for event categories; and a computer readable medium that carries instructions executable by the computer control system that, when executed: receive data from the seismic sensor; select an event of interest from the data received; determine a spectral estimate of the selected event of interest; compare the determined spectral estimate of the selected event of interest to the known spectral estimates; and select from the data received by the seismic source the orientation shot for orientation of the seismic sensor.

Abstract: Acoustic waves from a controllable downhole acoustic source in a cased borehole are focused into a region of an earth formation. A hydrophone is used to monitor acoustic signals for onset of cavitation. The estimated pressure from the source in the focus region provides an estimate of formation pore pressure.

Abstract: A method and apparatus for determining an effective cross-sectional area of a borehole including one or more sources for generating tube or Stoneley waves in the borehole; receivers for measuring amplitudes of the waves; and means to relate said measured amplitudes to said effective cross-sectional area or related parameters.

Abstract: The present disclosure is related to apparatuses and methods for estimating borehole parameters using a plurality of reflections caused by a plurality of acoustic pulses. The reflections may overlap each other and/or the acoustic pulses. The methods may include estimating an envelope of the received acoustic signal at the at least one element of the array of transducers; and estimating at least one arrival time of at least one of the plurality of overlapping events from the envelope of the received acoustic signals, the arrival times being characteristic of the geometry of the borehole. The method may also include imaging the borehole wall. The apparatus may include an array of transducers on a rotatable transducer assembly with at least one element on the array configured to generate a plurality of acoustic pulses and receive reflections and a processor configured to perform the method.

Abstract: In some embodiments, an apparatus and a system, as well as a method and an article, may include exciting a plurality of signal source pairs having a substantially equal and non-zero acoustic signature amplitude difference in a frequency domain to provide acoustic signal data, and acquiring the acoustic signal data along a selected azimuth. The plurality of signal source pairs may comprise acoustic bender plates, perhaps included in the outer wall of a downhole tool.

Abstract: Formation evaluation measurements are used to estimate formation lithology. The estimated lithology is used to provide an estimate of acoustic wave slowness. The estimated acoustic wave slowness is used to provide processing parameters for acoustic data that are less sensitive to noise.

Abstract: An apparatus and a method for migration of three components, 3-Dimensions seismic (3-C, 3-D) data acquired by down-hole receivers and surface seismic sources. This method utilizes full 3 components reflection wave field. It uses a dynamic, vector energy mapping method to image a reflection position and maps each time sample only to its reflected image point. Therefore, this method reduces unwanted data smearing and false mirror images. This method overcomes the weakness of using only a single component trace or pre-rotated three-component traces in the 1-C or 3-C 3-D VSP migration and produces better 3-D image.

Abstract: A method and apparatus for determining an effective cross-sectional area of a borehole including one or more sources for generating tube or Stoneley waves in the borehole; receivers for measuring amplitudes of the waves; and means to relate said measured amplitudes to said effective cross-sectional area or related parameters.

Abstract: In some embodiments, an apparatus and a system, as well as a method and an article, may include generating attenuation values associated with a set of multiple signals received by multiple receivers from a transmitted signal as a function of reception time and material velocity. The attenuation values may be stored in a memory and/or displayed on a display, perhaps in conjunction with a semblance map.

Abstract: Disclosed herein is a method of delineating a second wellbore from a first wellbore. The method includes, emitting acoustic waves from a tool in the first wellbore, receiving acoustic waves at the tool reflected from the second wellbore, and determining orientation and distance of at least a portion of the second wellbore relative to the tool.

Abstract: An apparatus and a method for migration of three components, 3-Dimensions seismic (3-C, 3-D) data acquired by down-hole receivers and surface seismic sources. This method utilizes full 3 components reflection wave field. It uses a dynamic, vector energy mapping method to image a reflection position and maps each time sample only to its reflected image point. Therefore, this method reduces unwanted data smearing and false mirror images. This method overcomes the weakness of using only a single component trace or pre-rotated three-component traces in the 1-C or 3-C 3-D VSP migration and produces better 3-D image.

Abstract: Measurements of acoustic velocities are made through a case borehole in the absence and presence of an applied magnetic field. A formation resistivity parameter may be estimated from differences in the acoustic velocities.

Abstract: Methods and systems for taking measurements related to subterranean formations. The methods and systems provide robust, reliable first arrival data for component signals of interest, which may be used to estimate formation slowness, characterize formation slowness zones, or act as an input to other processes. The methods and systems are capable of automatically providing good first arrival data based on signals received without any human interaction, and without setting or changing any parameters.

Abstract: Directional acoustic measurements made in the borehole are used for imaging a near-borehole geological formation structure and determination of its orientation. Four-component cross-dipole data set measured in a deviated borehole in combination with the directionality of the compressional waves in the dipole data give the orientation of bed boundaries crossing the borehole. The low-frequency content (2˜3 kHz) of the data allows for imaging the radial extent of the formation structure up to 15 m, greatly enhancing the penetration depth as compared to that obtained using conventional monopole compressional-wave data. A combination monopole/dipole arrangement of sources and receivers may also be used for imaging of bed boundaries.

Abstract: The present invention provides a method of performing the time picking step in a VSP (vertical seismic profile) survey. In a preferred embodiment of the invention the time picking step is carried out on a combined three-component amplitude of the received seismic energy, which contains the amplitude of all the seismic energy received at the receiver. The amplitude of the direct pulse in the combined trace will not decrease to zero as the offset of the source is changed, as can be the case for the single-component amplitude of the direct pulse. In a particularly preferred embodiment of the invention, the combined three-component amplitude is calculated by summing the Hilbert instantaneous amplitudes of the x-, y- and components of the seismic data using the equation (I). The present invention also provides two new time picks. One time pick involves finding the maximum positive gradient of A(t).

Abstract: A seismic signal is represented as a combination of a geologic signal and a noise signal. The representation of the seismic signal is decomposed into a linear combination of orthonormal components. One or more components are identified in which the geologic signal and the noise signal are uncorrelated. The noise signal is expanded as a product of an unknown noise amplitude modulation signal and a known noise spatial periodicity signal at the identified components. The expansion is solved for an estimate of the noise amplitude modulation signal at the identified components. The noise signal is estimated by multiplying the estimated noise amplitude modulation signal by the noise spatial periodicity signal. The estimated noise signal can be removed from the seismic signal to generate an estimate of the geologic signal.

Abstract: A method and system of dual wavefield reinforcement or increasing the contributions to each image point in the seismic image can be accomplished by aligning the upward traveling energy, U, and the downward traveling energy, D, and then summing U and D in the stacking process. A method of dual wavefield reinforcement includes receiving seismic data having both up going and down going wavefields. The up going wavefields are separated from the down going wavefields. Pre-NMO and post NMO statics for each of said up going and said down going wavefields are calculated. The determined pre-NMO static is applied to each of the up going and the down going wavefields. NMO/DMO stacking velocities for the seismic data on an up going wavefield floating datum is determined.

Abstract: A transducer configuration for use in acoustically imaging a target region behind an acoustically reflective layer includes a sonde having a geometrical center and constructed and arranged to support a plurality of transducers. The system includes a first transducer disposed within the sonde at a first distance from the geometrical center for generating a first acoustic pulse and for receiving a first acoustic signal. The acoustic signal comprises a first reflection from the reflective surface, a first set of fluid multiples arising from reflections between the reflective layer and a surface of the first transducer, and a first signal associated with the target area. The system also includes a second transducer disposed within the sonde at a second distance from the geometrical center for generating a second acoustic pulse and for receiving a second acoustic signal.

Abstract: A system for acoustically imaging a target region behind an acoustically reflective layer includes a transducer configuration for acquiring acoustic image data from the reflective layer and target region, wherein the reflective layer and target region are divided into voxels circumferentially disposed about a central point. The system includes a mechanism for processing the data comprising a transmitting transducer for transmitting a first acoustic pulse, a receiving transducer for detecting a first arrival of a first acoustic reflection signal associated with the first acoustic pulse, and a mechanism for suppressing multiple reflected signals from the acoustic reflection signal associated with the first acoustic pulse, wherein the suppressing mechanism facilitates the acquisition of image data from the target region.

Abstract: A method is disclosed for inverting 3-D seismic reflection data obtained from seismic surveys to derive impedance models for a subsurface region, and for inversion of multiple 3-D seismic surveys (i.e., 4-D seismic surveys) of the same subsurface volume, separated in time to allow for dynamic fluid migration, such that small scale structure and regions of fluid and dynamic fluid flow within the subsurface volume being studied can be identified. The method allows for the mapping and quantification of available hydrocarbons within a reservoir and is thus useful for hydrocarbon prospecting and reservoir management. An iterative seismic inversion scheme constrained by actual well log data which uses a time/depth dependent seismic source function is employed to derive impedance models from 3-D and 4-D seismic datasets. The impedance values can be region grown to better isolate the low impedance hydrocarbon bearing regions.

Abstract: An acoustic wave transducer useful in sonic logging while drilling a borehole through an adjacent earth formation includes an array of transducer elements mounted circumferentially around a drill collar. The elements are bonded in an elastomer ring that is received in an external groove in the collar and are protected by a shield having windows. The elements are electrically connected in parallel so that when excited by an electrical pulse, the elements generate a monopole acoustic wave that propagates out into the formation. When used as a receiver, the electrically connected array of elements detect averaged acoustic waves from the formation around the circumference of the drill collar and have minimum sensitivity to acoustic multipole waves traveling through the drill collar.

Abstract: A method for detecting alteration of earth formations penetrated by a wellbore. The method includes determining a first arrival velocity of dipole acoustic energy propagated through the earth formations. A first frequency dependent velocity of the dipole acoustic energy is then determined. A first dispersion characteristic is determined from the difference between the first arrival and frequency dependent velocities. The method includes determining a frequency dependent velocity and a first arrival velocity for synthesized waveforms for an unaltered formation. The synthesis uses the first arrival velocity of the dipole acoustic energy as a shear velocity. A second dispersion characteristic, related to a difference between the frequency dependent velocity and the first arrival velocity of the synthesized waveforms is determined. The alteration is detected by finding a difference between the first dispersion characteristic and the second dispersion characteristic.

Abstract: A method for using geometrical data to determine characteristics of a wellbore penetrating a subterranean formation is disclosed. The method involves converting data obtained form acoustic well logging into cartesian coordinates and solving a general quadratic equation by a least squares fit to an elliptical or circular model. More specific information, such as tensor strain and formation compaction along the wellbore may then be obtained from the geometrical data.

Abstract: Methods for determining an optimal frequency band for processing of flexural waves according to bias-corrected STC or QSTC are disclosed. A preliminary estimate of the formation shear slowness S and a determination of the borehole diameter D are first obtained, and the flexural waves are processed in a frequency band having a center frequency f.sub.c which is a function of preliminary estimate of S and the product of that estimate of S and diameter D. Where the preliminary estimate of S indicates a slow formation, f.sub.c is chosen as 0.6/SD. Where the estimate indicates a fast formation, f.sub.c is chosen as 0.2/SD. In other or all formations, a smooth function such as [0.2+((0.8/.pi.) arctan ((S-100)/100))/SD] can be used to choose the center frequency. Alternatively, if errors in the environmental parameters can be estimated statistically, they can be used to select an optimum center frequency. Once f.sub.

Abstract: The invention is a method of determining the thickness of a casing in a wellbore penetrating an earth formation using group delay determined casing resonance extracted from processed reflection signals from an acoustic pulse-echo imaging tool. A first Fourier transform coefficient series is calculated from the digitized reflection signal. Individual samples of the reflection signal are multiplied by their sample index values to obtain a modified digitized data string. A second Fourier transform coefficient series is calculated from the modified digitized data. The complex group delay function is calculated directly from the first and second Fourier coefficient series.

Abstract: Methods are provided which utilize a sonic tool for quantitatively determining parameters of a velocity profile of an altered zone in a rock formation traversed by a borehole. Synthetic amplitude information for the formation is generated by a computer model, by providing the computer with a proposed velocity profile for the formation, including values for parameters such as the radius of the altered zone and the acoustic velocities in the altered zone. The synthetic amplitude information is then compared with amplitude information (e.g. peak or total energy) of a compressional headwave as measured by the array sonic tool. If the comparison provides differences exceeding predetermined thresholds, the values for the parameters of the model are adjusted according to a least squares fit procedure until suitable values are found. The suitable values are then taken as the parameter values.

Abstract: An acoustic borehole logging system employs an acoustic tranmitter excited by a sweep frequency tone burst to produce an acoustic output having a free-field frequency spectrum of at least one resonant frequency of vibration. A closely-spaced acoustic receiver detects a borehole frequency spectrum that is representative of the acoustic transmitter free-field frequency spectrum altered by the effects of the properties of the subsurface formulation materials comprising the borehole wall. Such detected borehole frequency spectrum is recorded in correlation with depth as a log of the material properties of the subsurface formations surrounding the borehole.

Abstract: Amplifier gain is time ramped to increase amplification of the signal with increasing mud transit time and attenuation. Amplitude, ramp slope, and ramp onset time are independently controllable from the surface.

Abstract: In an acoustic logging system for providing information regarding selected parameters of the wall of a borehole in the earth, and of the rock formation which is adjacent the borehole, in which a single transmit/receive transducer system (T/RTS) mounted on a rotating assembly probes the wall of the borehole in a circular scanning pattern as a function of depth, the improvement which includes at least a second T/RTS mounted on the rotating assembly in known geometrical relation to the first T/RTS, and means to process two or more analog electrical scan signals for transmission over one or more electrical transmission channels in a logging cable. In particular, methods and means are described for the transmission of multiple scan signals, whereby more bottom hole parameters are transmitted, including composite electrical scan signals, in which the early part provides a gated high frequency scan signal and the latter part, the gated flow frequency scan signal, for greater penetration into the rock.

Abstract: Waveform data obtained in a borehole by a tool having a sonic source and an array of sonic detectors is analyzed to obtain an image of formation features within several tens of feet of the borehole, such as fractures, bed boundaries and other boreholes. A value of background sonic slowness is derived from the data and used to determine the sonic energy transit time from the source to each detector via each point in a grid of points extending into the formation and along the borehole. The time for a particular detector/point pair is used to extract the amplitude of the waveform from that detector at that time relative to operation of the source. Such amplitudes for the same point and for different detectors and tool positions are cumulated. The final values for all points are plotted as a variable density display which provides the desired image.

Abstract: Techniques are described whereby measurements derived from acoustic investigations made from inside a borehole penetraing an earth formation are factorized into components with high depth resolution. In one embodiment travel times of an acoustic wave such as the compressional is factored into mud travel time and interval travel times through the earth formation. In another embodiment amplitude measurements of an acoustic wave are factored into components such as receiver gain, earth formation attenuation, and coupling effectiveness at the boundary between the borehole and the earth formation. In both embodiments an additional component can be factored out that is a function of transmitter to receiver spacings. A modified Gauss-Seidel iteration technique is described whereby iterations can rapidly converge with less sensitivity to large variations in the measurements. Factorization of receiver gains effectively enables calibration of the receivers during well logging.

Abstract: The present invention is directed to an apparatus and method for obtaining azimuthally dependent measurements for evaluating the casing cement bond quality and, more particularly, for detecting and specifically locating channels or fissures between the casing and cement. The quality of the bond behind one or more arcs of known location on the casing is determinable by the present invention. The apparatus and method of the present invention employ a plurality of sonic transducers disposed in near contact with the casing in defined segmented locations about or around the exterior surface of a downhole tool. The transducers are arranged in a plurality of arrays, each array comprising four transducers, two transmitting and two receiving transducers, disposed along a single arc about or around the exterior of the tool.

Abstract: Disclosed are a well logging process and a well logging system using dipmeter and other logs to find subsurface faults and unconformities and automatically produce therefrom, and with user interaction, a subsurface map of the structural and depositional environment and stratigraphic characteristics of subsurface formations particularly important in the search for and exploitation of subsurface resources such as hydrocarbons.

Abstract: A borehole televiewer logging tool employs a transducer assembly having a transmitter of acoustic energy pulses and a receiver of acoustic energy pulses representing reflections of the transmitted acoustic energy pulses from the walls of a borehole traversing a subsurface formation. The transducer assembly is rotated within the borehole and also advanced along the borehole. The received reflection signals are corrected for amplitude modulation resulting from oblique angles of incidence of the transmitted acoustic energy pulses when the logging tool is off-center of the borehole, is in an eliptical borehole, or is tilted from the vertical axis of the borehole. The corrected reflection signals modulate an image display so that the full 360.degree. of the borehole wall can be delineated.

Abstract: An acoustic well logging method employing a tool having at least two acoustic transmitters and at least two acoustic receivers. In a preferred embodiment, one receiver is positioned midway between the two transmitters, and the other receiver is spaced from the first receiver along the longitudinal axis of the tool between the transmitters. Two signals, each representing an acoustic wave that has propagated from a transmitter through a portion of the formation surrounding the borehole to a receiver, are recorded when the tool is in each of two positions relative to the longitudinal axis of the well. In each of the tool positions, one recorded signal is associated with the midpoint receiver and the other with another receiver. From the four recorded signals, a new signal is generated. This derived signal has Fourier amplitude spectrum indicative of the formation parameters, but is independent of components associated with the transmitters and receivers.

Abstract: A method of sonic logging in which there is established at a depth of interest in a borehole a set of peak matrices comprised of peak vectors representative of a plurality of different characteristics of sonic signals traversing an earth formation. A set of rules is established based upon borehole sonic characteristics including the utilization of past histories of slowness and coherence values of wave components of interest. The matrices are searched in accordance with the rules to identify the presence in the sonic signals of wave components of interest, such, for example, as casing, compressional, shear and Stoneley. The identified wave components are recorded as a function of depth of interest, and the aforesaid steps are repeated at each depth of interest.

Abstract: A method for producing a display of acoustic signals received during full waveform acoustic well logging. In a preferred embodiment, the signals received at the individual receiver (or receivers) of the logging tool are stacked along lines of constant acoustic velocity to produce for display a stacked signal. Preferably, the raw signals are weighted prior to the stacking step, to compensate for decreasing amplitude of the acoustic arrival of interest with increasing transmitter to receiver distance. The stacked signals produced may be displayed in various formats, such as on a linear or logarithmic scale of inverse acoustic velocity, or of formation porosity.

Abstract: In the apparatus and method of the invention, acoustic energy is propagated in two slightly differing, or offset, circumferential paths in such a way as to interact with the formation under investigation. The propagating energy is detected and the resulting waveforms are compared using semblance. The waveforms corresponding to the respective paths will be quite similar provided that the length of the paths are equal and that there are no fractures or other similar anomalies between the source and receiver. The waveforms for the respective paths will be quite dissimilar, however, if a fracture or similar anomaly does lie between the source and receiver for the respective paths. The semblance may be displayed in log format.