A hydrophone vertical seismic profiling experiment

Geophysics ◽  
1988 ◽  
Vol 53 (11) ◽  
pp. 1437-1444 ◽  
Author(s):  
Thomas L. Marzetta ◽  
Marion Orton ◽  
Alfred Krampe ◽  
Lucian K. Johnston ◽  
Paul C. Wuenschel
Keyword(s):  
Body Wave ◽  
Vertical Array ◽  
Pressure Signal ◽  
Vertical Seismic Profiling ◽  
Vsp Data ◽  
First Arrival ◽  
Tube Wave ◽  
The Cost ◽  
Velocity Filtering ◽  
Hydrophone Array

To reduce the cost of VSP data acquisition, it is necessary to record the VSP signal from a vertical array of geophones for a single operation of the source. Until a vertical array of clamped three‐component geophones is available, it seems logical to evaluate the capabilities of a vertical array of hydrophones, which is much easier to fabricate. It is well known that elastic waves in the solid couple to pressure waves in the borehole fluid. It is also well known that this coupling excites in the borehole fluid energy known as tube‐wave noise that dominates the borehole pressure signal after the first arrival. (The borehole acts as a waveguide.) In this paper we test the effectiveness of velocity filtering of the borehole pressure signal to attenuate the slowly propagating tube‐wave noise and enhance the faster propagating body‐wave signals. Our initial test satisfactorily extracted from the hydrophone array data a strong reflected event that was also observed in the conventional clamped geophone VSP taken in the same borehole. We were not as successful in recovering subsequent weaker reflected signals from the hydrophone data, because of the strong incoherent ambient tube‐wave noise. This incoherency resulted from instrumental limitations that allowed us to record, for each shot, only three of the twelve hydrophone channels available in the vertical array.

An examination of tube wave noise in vertical seismic profiling data

Geophysics ◽  
1981 ◽  
Vol 46 (6) ◽  
pp. 892-903 ◽  
Author(s):  
B. A. Hardage
Keyword(s):  
Body Wave ◽  
Effective Means ◽  
Power Spectra ◽  
Effective Field ◽  
The Body ◽  
Seismic Profiles ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Vsp Data ◽  
Tube Wave

Tube waves act as noise that camouflages upgoing and downgoing body wave events which are the fundamental seismic data measured in vertical seismic profiling (VSP). In two onshore vertical seismic profiles, the principal source of tube waves is shown to be surface ground roll that sweeps across the well head. Secondary tube wave sources revealed in these VSP data are the downhole geophone tool itself and the bottom of the borehole. Body wave signals are also shown to create tube waves when they arrive at significant impedance contrasts in the borehole such as changes in casing diameter. Computer simulated vertical geophone arrays are used to reduce these tube waves, but such arrays attenuate and filter body wave events unless static time shifts are made so that the body wave signal occurs at the same two‐way time at each geophone station. Consequently, actual downhole vertical geophone arrays are not an effective means by which tube waves can be eliminated. Power spectra comparisons of tube wave and compressional body wave events demonstrate that band‐pass filters designed to eliminate tube waves also suppress body wave signals. A simple but effective field technique for reducing tube waves is shown to be proper source offset. Using velocity filters to retrieve upgoing compressional events from VSP data heavily contaminated with tube wave noise yields in one example an agreement with surface measured reflections that is superior to that obtained from synthetic seismograms calculated from log data recorded in the same well.

Analysis and removal of multiply scattered tube waves

Geophysics ◽  
2000 ◽  
Vol 65 (3) ◽  
pp. 745-754 ◽  
Author(s):  
Gérard C. Herman ◽  
Paul A. Milligan ◽  
Qicheng Dong ◽  
James W. Rector
Keyword(s):  
Wave Field ◽  
Large Amplitude ◽  
Data Set ◽  
Impedance Function ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Total Data ◽  
Vsp Data ◽  
Tube Wave

Because of irregularities in or near the borehole, vertical seismic profiling (VSP) or crosswell data can be contaminated with scattered tube waves. These can have a large amplitude and can interfere with weaker upcoming reflections, destroying their continuity. This type of organized noise cannot always be removed with filtering methods currently in use. We propose a method based on modeling the scattered tube‐wave field and then subtracting it from the total data set. We assume that the scattering occurs close to the borehole axis and therefore use a 1-D impedance function to characterize borehole irregularities. Estimation of this impedance function is one of the first steps. Our method also accounts for multiply scattered tube waves. We apply the method to an actual VSP data set and conclude that the continuity of reflected, upcoming events improves significantly in a washout zone.

Hydrophone VSP imaging at a shallow site

Geophysics ◽  
1997 ◽  
Vol 62 (3) ◽  
pp. 842-852 ◽  
Author(s):  
Paul A. Milligan ◽  
James W. Rector ◽  
Robert W. Bainer
Keyword(s):  
Primary Source ◽  
Acquisition Time ◽  
Coherent Noise ◽  
Cross Sectional ◽  
Reflection Data ◽  
Shallow Site ◽  
Vsp Data ◽  
Mapping Techniques ◽  
Tube Wave ◽  
Hydrophone Array

We evaluated the capabilities of vertical seismic profiling (VSP) for imaging the complex heterogeneous unconsolidated sedimentary structures at a shallow site. We deployed a 24‐level hydrophone array with 0.5-m level spacing down a preexisting poly vinyl chloride (PVC) cased well. Data acquisition time was quick. Only 15 multioffset shot points using a hammer‐on‐plate source were needed to acquire reflection data between the water table at 3 m and the bedrock at 35 m to produce a depth section image. This image extended 9 m from the receiver well, yielding resolutions between fresh‐water‐bearing sands and impermeable muds and clays of better than 1 m. Depth accuracy of the image was confirmed by good correlation with cone penetrometer logs. We used conventional wavefield separation and VSP-CDP mapping techniques to image the data. Tube waves, created by seismic arrivals at cross‐sectional area changes in the borehole fluid column, were the primary source of coherent noise in the data. The tube‐wave arrival structure was complicated by the hydrophone array, which generated and scattered tube waves at each hydrophone pod. To combat the tube wave interference, we inserted closed‐cell‐foam baffles between elements. The baffles attenuated and slowed the tube waves, and reduced generation and scattering. A comparison between unbaffled and baffled VSP data showed that baffling increased the maximum useful frequency from 300 Hz to over 900 Hz. By contrast, surface shot data recorded at the same site, using buried 40-Hz vertical geophones, exhibited useful frequencies of less than 250 Hz. In addition, coherent noise in surface shot records caused by air waves and first arrivals made it very difficult to identify shallow reflections above 25 m. Reflections from depths as shallow as 10 m were easy to identify in the baffled VSP data.

scholarly journals An extraction method of dispersion curve from vertical seismic profiling data

2020 ◽  
Author(s):  
Zhi Hu ◽  
Jinghuai Gao ◽  
Yanbin He ◽  
Guowei Zhang
Keyword(s):  
Dispersion Curve ◽  
Group Velocity ◽  
Body Wave ◽  
Seismic Signal ◽  
Time Frequency ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Wave Data ◽  
Vsp Data ◽  
The Relationship

Abstract The dispersion curve describes the relationship between velocities and frequencies. The group velocity is a kind of dispersion, which presents the velocities of the energy with different frequencies. Although many studies have shown methods for estimating group velocity from a surface wave, the estimation of group velocity from body-wave data is still hard. In this paper, we propose a method to calculate the group velocity from vertical seismic profiling (VSP) data that is a kind of body-wave data. The generalised S-transform (GST) is used to map the seismic signal to the time-frequency (TF) domain and then the group delay (GD) can be extracted from the TF domain. The GD shows the travelling time of different frequency components. The group velocity can be calculated by the GD and the distance between receivers. Unfortunately, the GD is hard to measure accurately because of the noise. Inaccurate GD introduces errors in estimating the velocity. To reduce the errors, we make use of the multiple traces and the iterative least-squares fitting to extract the relationship line between GD and depths. The slope of the line is the reciprocal of the group velocity. Two numerical examples prove the effectiveness of the method. We also derive the formula of group velocity in diffusive-viscous media. In the field data example, the dispersion intensity at different depths and the geological layers can be well matched. These examples illustrate the proposed method is an alternative method for dispersion estimation from VSP.

scholarly journals Experimental testing of semirigid corrugated baffles for the suppression of tube waves in vertical seismic profile data

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. D131-D149 ◽  
Author(s):  
Andrew Greenwood ◽  
J. Christian Dupuis ◽  
Anton Kepic ◽  
Milovan Urosevic
Keyword(s):  
Wave Attenuation ◽  
Experimental Testing ◽  
Low Cost ◽  
High Amplitude ◽  
Seismic Profile ◽  
Vertical Seismic Profile ◽  
Vsp Data ◽  
Scale Experiment ◽  
Tube Wave ◽  
The Cost

Multichannel borehole hydrophone strings are a low-cost, low-risk, alternative to borehole clamping geophones. Vertical seismic profile (VSP) data collected with hydrophones, however, suffer from high-amplitude coherent tube-wave noise. This reduces the usable data to the first arrivals and traveltimes for check-shot surveys. To significantly reduce tube-wave noise from VSP data acquired with hydrophones, we have designed and tested a novel tube-wave attenuation baffle. The effectiveness of the baffle was first verified in a laboratory-scale experiment and then in a borehole drilled into a hardrock environment. The laboratory experiments tested the performance of four different baffle topologies, whereby the best performing topology was the semirigid corrugated pipe baffle. This design reduced the amplitude of the tube wave with more than 40 dB and was logistically easy to deploy. The field experiment investigated the effectiveness of three different semirigid corrugated pipe baffle topologies in a PQ (123 mm) diamond drillhole in Western Australia. Here, we found that the semirigid corrugated pipe baffle was effective in disrupting tube-wave propagation. The 100 mm diameter baffle achieved an impressive 60 dB of tube-wave attenuation, whereas the 50 mm baffle had a modest attenuation of 10–15 dB. This suggests that the performance of this new type of baffle is best when the diameter of the baffle is closely matched to the diameter of the borehole. The results of these experiments have significant implications because hydrophone arrays with a large number of receivers are comparatively inexpensive and simpler to deploy than borehole geophone counterparts. The development of hydrophone arrays that are free of interfering borehole modes could allow VSPs to be acquired in situations in which seismic-polarity information is not required and could help VSP gain traction in cases in which the cost of acquisition has precluded its use until now.

A blind interpretation of drill‐bit signals

Geophysics ◽  
2000 ◽  
Vol 65 (3) ◽  
pp. 970-978 ◽  
Author(s):  
Flavio Poletto
Keyword(s):  
Seismic Signal ◽  
Dominant Frequency ◽  
Drill Bit ◽  
Coherent Noise ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Vsp Data ◽  
First Arrival

The role of kurtosis in evaluating the quality of vertical seismic profiling (VSP) drill‐bit data is investigated. The calculations show how kurtosis depends on the dominant frequency, bandwidth, and phase content of a seismic signal. This analysis is applied to synthetic and real common‐offset and common‐shot drill‐bit seismograms to evaluate the prominence and quality of the first arrival and other coherent events. High values of kurtosis correspond to an isolated first arrival or to a compressed coherent noise event, while low values are typical of low S/N (distributed) ratio traces. Kurtosis analysis applied to drill‐bit VSP data while drilling proved to be successful at identifying high‐quality traces with little interpretational input.

scholarly journals Recording seismic reflections using rigidly interconnected geophones

Geophysics ◽  
2001 ◽  
Vol 66 (6) ◽  
pp. 1838-1842 ◽  
Author(s):  
C. M. Schmeissner ◽  
K. T. Spikes ◽  
D. W. Steeples
Keyword(s):  
Wave Propagation ◽  
Data Acquisition ◽  
Seismic Reflection ◽  
Spatial Sampling ◽  
P Wave ◽  
Signal Distortion ◽  
Reflection And Refraction ◽  
First Arrival ◽  
The Cost ◽  
Seismic Reflections

Ultrashallow seismic reflection surveys require dense spatial sampling during data acquisition, which increases their cost. In previous efforts to find ways to reduce these costs, we connected geophones rigidly to pieces of channel iron attached to a farm implement. This method allowed us to plant the geophones in the ground quickly and automatically. The rigidly interconnected geophones used in these earlier studies detected first‐arrival energy along with minor interfering seismic modes, but they did not detect seismic reflections. To examine further the feasibility of developing rigid geophone emplacement systems to detect seismic reflections, we experimented with four pieces of channel iron, each 2.7 m long and 10 cm wide. Each segment was equipped with 18 geophones rigidly attached to the channel iron at 15‐cm intervals, and the spikes attached to all 18 geophones were pushed into the ground simultaneously. The geophones detected both refracted and reflected energy; however, no significant signal distortion or interference attributable to the rigid coupling of the geophones to the channel iron was observed in the data. The interfering seismic modes mentioned from the previous experiments were not detected, nor was any P‐wave propagation noted within the channel iron. These results show promise for automating and reducing the cost of ultrashallow seismic reflection and refraction surveys.

scholarly journals Appraising structural interpretations using seismic data — Theoretical elements

Geophysics ◽  
2019 ◽  
Vol 84 (2) ◽  
pp. N29-N40
Author(s):  
Modeste Irakarama ◽  
Paul Cupillard ◽  
Guillaume Caumon ◽  
Paul Sava ◽  
Jonathan Edwards
Keyword(s):  
Seismic Data ◽  
Structural Model ◽  
Synthetic Data ◽  
Target Region ◽  
Structural Interpretation ◽  
Vertical Seismic Profiling ◽  
Seismic Image ◽  
Vsp Data ◽  
Phase Shift Data ◽  
Seismic Images

Structural interpretation of seismic images can be highly subjective, especially in complex geologic settings. A single seismic image will often support multiple geologically valid interpretations. However, it is usually difficult to determine which of those interpretations are more likely than others. We have referred to this problem as structural model appraisal. We have developed the use of misfit functions to rank and appraise multiple interpretations of a given seismic image. Given a set of possible interpretations, we compute synthetic data for each structural interpretation, and then we compare these synthetic data against observed seismic data; this allows us to assign a data-misfit value to each structural interpretation. Our aim is to find data-misfit functions that enable a ranking of interpretations. To do so, we formalize the problem of appraising structural interpretations using seismic data and we derive a set of conditions to be satisfied by the data-misfit function for a successful appraisal. We investigate vertical seismic profiling (VSP) and surface seismic configurations. An application of the proposed method to a realistic synthetic model shows promising results for appraising structural interpretations using VSP data, provided that the target region is well-illuminated. However, we find appraising structural interpretations using surface seismic data to be more challenging, mainly due to the difficulty of computing phase-shift data misfits.

scholarly journals Tube Wave removal from vertical seismic profiling (VSP) surveys

2012 ◽  
Vol 2012 (1) ◽  
pp. 1-4
Author(s):  
Dariush Nadri ◽  
Milovan Urosevic ◽  
Paul Wilkes ◽  
Mehdi Asgharzadeh
Keyword(s):  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Tube Wave
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