Abstract:
Méthode d'amélioration de la qualité des données vibrosismiques, particulièrement celles acquises en mode slip-sweep, par estimation et atténuation des différentes composantes harmoniques (voir fig. 3). On estime ces composantes à partir du signal Ground-Force, par une technique de séparation à deux options, moindres carrées, ou temps-fréquence, toutes deux adaptées à la composante à extraire et on subdivise ce bruit en classes. On calcule les harmoniques propres à l'enregistrement considéré et on procède à leur soustraction. On calcule enfin les bruits de référence relatifs à chaque classe et on procède à leur ré-estimation par une méthode à entrées/sorties multiples avec prise en charge dynamique de la bande fréquentielle, réalisable selon l'une des trois options : globale, cascade ou multi-référence, puis soustraction de l'enregistrement contaminé. On améliore la qualité des données, par une mise en forme appropriée du signal source.
Abstract:
A method of seismic surveying using one or more vibrational seismic energy sources activated by sweep signals. The highest order harmonic that has sufficient strength to cause significant harmonic distortion of a sweep segment is determined. A number of sweep segments in excess of the number of sources is selected. Initial phase angles are selected for each sweep segment of each seismic energy source so that substantially all harmonics up to and including the highest order harmonic are suppressed. Using cascaded sweeps, seismic data are acquired and processed to substantially attenuate harmonics upto the selected order.
Abstract:
Methods and systems for separating seismic data acquired using a plurality of substantially simultaneously fired sources are described. The sources use sweep sequences having low cross correlation levels to generate seismic waves, and their source signatures are determined. Using the source signatures, the wave fields associated with each of the sources are extracted from the seismic data by, for example, performing a time domain deconvolution.
Abstract:
Adaptive filtering method to remove ground roll from seismic data. In an M channel adaptive filter, weights Wi are set using an adaptive algorithm based on seeking the minimum in the partial differential of cost function J. The cost function includes an expansion of the primary trace d into d = dg + ?d (where: dg is ground roll contribution and ?d = dsig + dran, where dsig is the reflected signal component and dran is a random noise component) and a corresponding expansion of the reference x into x = xg + ?x (where xg is ground roll contribution and ?x = xsig + xran; where xsig is a reflected signal component and xran is a random noise component). The delta components are included in the denominator of cost function J to provide an optimal solution of the filter coefficients biased by the reflection signal and random noise is removed.
Abstract:
A method for recording and pre-processing high fidelity vibratory seismic data includes measuring the motion of the vibrator (36) which is related to the vibrator applied force times a transfer function of minimum phase, causal, linar system relating the actual vibrator output with the measured vibrator motion, determining a ratio (52) by dividing the vibratory seismic data by the measured motion of the vibrator to remove the unknown applied force leaving the earcj reflectivity times a time derivative divided by a minimum phase function, minimum phase band pass filtering the resulting ratio and performing mimimum phase deconvolution to remove the time derivative divided by the transfer function of mimimum phase. The method may also include the steps of receiver ensemble deconvolution (56), statics correction (58), F-K filtering for noise (60), zero phase spiking deconvolution (64) and model dephasing (66). The actual signal that the vibrator (36) is sending into the ground is used in pre-processing.
Abstract:
A method for generating a cement bond log, in some embodiments, comprises transmitting sonic or ultrasonic waves in multiple directions from a logging tool disposed in a wellbore, receiving reflected waves at the logging tool and recording waveforms based on the received waves, processing the waveforms to determine numerical values that indicate a degree of bonding associated with multiple portions of a cement sheath disposed in the wellbore, aggregating the numerical values, and generating a composite image based on the aggregated numerical values.
Abstract:
The method of acquiring seismic data comprises: allocating respective binary sequences to a plurality of seismic sources (30); emitting seismic waves into a medium during an acquisition time from the plurality of seismic sources, the acquisition time being divided into a plurality of slots and activation of a seismic source in the slots being conditioned by respective bits of the binary sequence allocated to that seismic source; obtaining a seismic signal sensed by a receiver (15) after propagation of the emitted seismic waves in the medium; and combining the seismic signal with the binary sequence allocated to one of the seismic sources.
Abstract:
The invention relates to a method for improving the quality of vibroseismic data, particularly vibroseismic data acquired in slip-sweep mode, by estimation and attenuation of the different harmonic components (see fig. 3). Said components are estimated from the Ground-Force signal using a separation technique with two options, namely least squares or time-frequency, both of which are adapted to the component to be extracted, and the noise is subdivided into classes. The harmonics specific to the recording in question are calculated and subtracted. Finally, the reference noises relative to each class are calculated and re-estimated using a multiple input/output method with dynamic management of the frequency band, which can be achieved using one of three options: global, cascade or multi-reference, followed by subtraction from the contaminated recording. The data quality is improved by means of appropriate source signal shaping.
Abstract:
Methods and instrumentation for detecting and representing at least one geologic formation in front of an operating drill-bit using the vibration noise generated by the operating drill-bit as a source, comprising at least one receive array comprising more than one receive vibration sensor elements, said at least one receive array are located in one or both of i) at least one receive well, and ii) submerged in water for sub-sea operation, and beam forming at least one receive signal from the signals from said more than one receive elements of said at least one receive array, and forming at least one reference signal representing the vibrations of the operating drill-bit, and correlating said at least one receive signal with said at least one reference signal with different correlation lags, and forming a seismic representation of the at least one geologic formation in front of the drill-bit through said correlating.