Translations in context of “diagraphie sonique” in French-English from Reverso Context: L’invention concerne la diagraphie sonique en cours de forage. Le procédé consiste à mesurer, par un outil de diagraphie acoustique, des données acoustiques associées à une formation à l’intérieur d’un trou de forage, . Institut Français du Pétrole. Résumé. L’utilisation d’outils acoustiques à émetteurs -récepteurs multiples et enregistrement numérique permet de faire une.
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The fule waveforms recorded by an array of receivers in a borehole sonic tool contain diagraphis set of waves that can be fruitfully used to obtain detailed information about the nearborehole lithology and structure.
Each wave contains information that can be disturbed by the presence of the other waves. The great amount of full-waveform sonic data leads geophysicists and log analysts to implement algorithms for separating waves.
The log analyst diargaphie pay attention to the choice of parameters for acquisition. The acoustic data must be recorded with well suited spatial and temporal sampling-rates to avoid spatial and temporal aliasings.
DIAGRAPHIE SONIQUE (sonic logging): Topics by
The efficiency of the wave-separation algorithms depends on the choice of acoustic data gathers. Acoustic data are sorted either in a common-shot gather or in a constant-offset gather. The wave separation filters commonly used are apparent velocity filters. Less usual filters are a Wiener filter and a spectral matrix filter. The efficiency of an apparent velocity filter is enhanced by application of spectrum equalization.
The signal to noise ratio is enhanced by spectral matrix filtering. We describe different processing sequences applied to a set of field examples. The sonic tool used was a Schlumberger Dipole Imaging tool. The receiver section contains eight dipole-monopole stations spanning 3. The distance between the monopole transmitter and the first receiver station is 9 ft. The source was fired at equal spacings of 6 inches throughout the open hole section.
For this experiment, the monopole transmitter was activated with a low frequency pulse for the purpose of generating low frequency Stoneley waves. The full waveforms taken at each receiver were recorded on magnetic tape. In the part of the well studied, the reservoir layers are clean sandstones or shaly sandstones overlain by impervious shale cap rock.
The well is completed by a casing down to the top of the reservoir layers. The sonic data were recorded to study the reflected Stoneley waves. The borehole Stoneley waves are trapped modes that can be reflected when the direct borehole Stoneley wave encounters permeable fractures Hornby, Johnson, Winkler and Plumb, or a major change in lithology Hornby, Figure 6 shows the common shot gather processing applied to the waveforms recorded when the source was at depth The figure shows, from right to left, the raw data Athe flattened raw data Bthe first eigensection obtained by matrix spectral filtering C and its associated residual eigensection D.
These sonic sections were time shifted to be directly comparable with the raw data, using the picked time of the direct wave arrival. Sonic section E shows the direct Stoneley wave and its downgoing reflected waves mainly between 13 and 15 ms.
Sonic section F shows the upgoing reflected Stoneley waves. Figure 7 shows a constant offset gather. On this section we can observe good correlation between the frequency log and lithology derived from an independent analysis.
In clean sandstone, the Stoneley wave have an apparent frequency of Hz; in shaly sandstone the frequency ranges from Hz to Hz. The value of the Stoneley frequency is directly related to shaliness.
Maximum shalk ness is observed in the depth interval. Figure 8 shows from top to bottom the slowness and the standard deviation of the slowness computed from raw sonic data and filtered sonic data first eigensection as well as the frequency log and its standard deviation.
After filtering, the standard deviation is reduced whatever the depth, but mainly in the depth interval. This depth interval is associated with maximum shaliness. The maximum standard deviation observed at m is due to the interference of downgoing reflected waves and a direct Stoneley wave.
This reflected Stoneley wave is not filtered in the commonshot gather space. Figure 9 shows the energy log derived from the set of first eigenvalues associated with the first eigensections.
This log correlates in depth with the frequency log and exhibits the interval depth where the reflected downgoing Stoneley waves are very strong. Figs 10 to 13 show the sonic fullwaveform sections after constant offset gather processing. This sonic section mainly contains upgoing reflected Stoneley waves. The sonic section shown in Figure 10 has been filtered in order to separate the direct Stoneley wave and downgoing reflected Stoneley waves.
The results are diagraohie in Figs. In the configuration used, the distance between two receivers was 50 cm. The distance between the monopole transmitter and the first receiver station was 3. The source was fired at equal spacings of 5 cm throughout the open hole section of the well. The sonic data were used to compute an accurate compressional-wave velocity-log obtained after picking of the refracted arrivals Fig.
For that purpose, the sonic data were collected in constant offset gathers. For each gather Fig. Each filter was applied in diagraphle time-window in order to select a specific wave. After filtering, the residual sonic section contains the noise and the other waves. In this field case, wave separation was performed in two steps. In the first step, a Wiener filter was applied in diaggaphie 2-to-5 ms time-interval.
It was used to enhance the interface modes Fig. The interface modes are very different in, sandstones and in shales. The transition between these two geological formations are clearly marked at 1 m. In shales 1 – 1 m depth intervalthe interface modes have a high frequency content and propagate with a constant velocity, which is the mud velocity. They are mud waves. In sandstones, the interface modes have strong amplitudes and a low frequency content.
They are Stoneley waves. After filtering, the residual sonic section shows the refracted modes and the leaky modes Fig. In sandstones, we can notice a residue of Stoneley modes at about 2.
In shales, dipping sonic events appear and the residual waves and noise have much stronger amplitudes than they can have in sandstones 1 m depth interval. In the second step, a Wiener filter was applied to the constant-offset sonic-data gather, after elimination of interface modes.
The filter was applied in the 0 to 2. The residual constant-offset section was corrected for normal moveout using the velocity function derived from the acoustic log. At about 1 m, diffractions can be observed on the filtered sonic section Fig. The interpretation of these diffracted patterns shows that they were created by heterogeneities in the shale medium due to dolomitic intercalations situated about 4 m from the well.
Note that the diffractions, at the acoustic log scale, appear as variations in the shape of the reflected event associated with the dolomitic zone, at the VSP-CDP stack scale Fig. The vertical well was drilled to establish a vertical geologic cross-section of the quarry and to identify the acoustic impedance variation boundaries. The set of logs includes: Full waveform acoustic data were recorded using a specific acoustic tool assembly in order to obtain a common-shotpoint gather.
The source-receiver distance varied from 3. The recording length was 10 ms.
Translation of “diagraphie sonique” in English
The receiver spacing was 1 cm. In the common-shot gather, the refracted arrivals and borehole modes have linear moveout across the offset range, while the reflected events have hyperbolic moveout. Under these conditions, all the refracted arrivals and borehole modes can easily be filtered by a set of apparent velocity filters. Each filter is designed to cancel a selected wave, characterized by its velocity.
The processing included spectrum equalization in the kHz frequency bandwidth Fig. After processing, the acoustic data Fig. These reflections come from reflectors situated in the oolithe blanche reservoir layer up to a distance of approximately 10 m. The use of information coming from vertical well VSP and log and synthetic modeling leads us to differentiate the reflections coming from discontinuities situated above A and below B the horizontal well.
Another way is to use an acoustic logging aonique with a modified radiation-pattern in order to illuminate either aboveor belowdiscontinuities. Data correspond to usage on the plateform after Xiagraphie current usage metrics is available hours after online publication and is updated daily on week days.
Metrics Show article metrics. Services Same authors – Google Scholar. IFP Energies nouvelles, Vol. Current usage metrics About article metrics Return to article. Initial download of the metrics may take a while. Volume 47, Number 2March-April