FK Filtering Research Articles

An unsupervised machine learning algorithm approach using K-Means Clustering for optimizing Surface Wave Filtering in seismic reflection data

Surface waves often cause significant noise in seismic data, complicating the interpretation of subsurface structures. Traditional filtering methods, such as FK filtering, usually struggle with non-stationary noise and require extensive manual parameter tuning. This study explores the effectiveness of using K-means clustering, incorporating attributes such as amplitude, frequency, and phase to filter surface waves from seismic data. Synthetic seismic data were first generated to test the proposed method, ensuring its robustness before application to real field data. Attributes were extracted from each seismic trace, including instantaneous amplitude, frequency, and phase. These attributes were used as input parameters for the K-means clustering algorithm. The identified clusters corresponding to surface waves were then used to filter these waves from the seismic data. The K-Means clustering effectively differentiated surface waves from reflected waves in both synthetic and real seismic datasets. The method demonstrated that by including phase as an attribute, alongside amplitude and frequency, the accuracy of surface wave detection and filtering significantly improved. The synthetic data showed a clear separation of wave types, validating the method. When applied to real field data, the approach consistently removed surface waves, clarity of seismic reflections crucial for subsurface analysis.

Ground roll intelligent suppression based on spatial domain synchrosqueezing wavelet transform convolutional neural network

AbstractGround roll is usually considered as a common linear noise in land seismic data. The existence of the ground roll often masks the effective reflection information of underground media, resulting in the deterioration of seismic data quality. Therefore, ground roll suppression is one of the main tasks in seismic data processing. A large number of previous studies have proved that the time‐frequency signal processing method based on mathematical transformation has shown excellent performance in ground roll attenuation and still has development potential. Meanwhile, a convolutional neural network, as one of the popular deep learning technologies, has also been widely used in the field of seismic signal processing. In this paper, we combine the convolutional neural network with the time‐frequency signal processing method based on mathematical transformation, that is, spatial domain synchrosqueezing wavelet transform, and propose a complete ground roll suppression workflow of shot gathers in spatial wavenumber domain, realizing high‐precision and automatic ground roll removal. Field data examples show that compared with bandpass filtering, FK filtering, time domain synchrosqueezing wavelet transform, spatial domain synchrosqueezing wavelet transform and the convolutional neural network, the spatial domain synchrosqueezing wavelet transform convolutional neural network has achieved satisfactory results in effectively attenuating ground roll and retaining valid information.

Application of Noise Attenuation on 2D Shallow Offshore Seismic Reflection Data: A Case Study from the Baltic Sea

Noise is always present in offshore seismic data, as there isn't a single method that could eliminate all the forms of noise. In this study, noise removal techniques were applied to attenuate different noises in 2D shallow-marine seismic data from the Baltic Sea area. Amplitude recovery should be applied before the noise attenuation stage as a preconditioning process for showing all noises in the deeper part of the seismic data. Frequency filters (notch filter and low-cut filter), frequency-wavenumber (FK) filter, and swell noise attenuation (Deswell) were applied as robust noise attenuation techniques. The method of directly modifying the amplitude spectrum of the seismic data is known as frequency filtering. A notch filter can be used to remove the harmonic noise of the power line harmonic noise (mono-frequency noise). A low-cut filter can be used to remove the low-frequency noises due to the influence of hydrostatic pressure variations. The linearly correlated events, such as tail-buoy and operational noise, were removed using the FK filter. Incoherent noise, such as swell noise, can be attenuated by swell noise attenuation (Deswell). The seismic results are displayed before and after the applied noise attenuation techniques to prove the validity of the applied filters. This study aimed to show the importance of shallow offshore seismic data processing in removing different types of noise, as it increases the value of data for seismic data interpretation and marine geohazard assessment.

Integrity Testing of a Platform‐Pile System Using a Sensor Array and Wavenumber Domain Analysis

Appropriate impact and sensor locations must be chosen in pile integrity tests to prevent three‐dimensional effects caused by the torsional and flexural modes. The three‐dimensional characteristics cause high‐frequency interference, especially in bridge and wharf piles. A method is required to minimize the high‐frequency interference without reducing the accuracy of the pile integrity test. A multivelocity integrity test method is proposed based on a sensor array and frequency‐wavenumber (FK) domain analysis to eliminate high‐frequency interference and reduce the errors in the output of integrity tests of platform‐pile systems. FK filtering is performed to eliminate the spatial alias frequency and separate the upward and downward wavefield and the vibration modes in an integrity test of a platform‐pile system. The optimum sensor location to minimize the influence of interference signals is at the bending plane relative to the impact location. Using a sensor array reduces the influence of the sensor location on the test results and minimizes the requirements for determining the location of the excitation point and sensors in the traditional low‐strain integrity testing (LST) method, thereby improving the applicability of this method.

Attenuation of the Multiple Reflection-Refraction in 2-D Common-Shot Gather via Random-Derangement-Based FX Cadzow Filter

The attenuation of coherent noise plays a crucial role in reflection seismology but still poses some technical challenges. The multiple reflection-refraction (MRR) is one of the main coherent noises in land seismic surveys. The Cadzow filter can effectively attenuate incoherent noise. But it struggles in attenuating coherent noise. After keeping reflection events relatively horizontal, some researchers randomly rearrange the trace orders of the input data to realign coherent noise in an incoherent position so that the Cadzow filter can treat the realigned coherent noise as incoherent noise. Accordingly, a random-derangement-based FX Cadzow filter is proposed to attenuate MRRs in 2-D common-shot gathers based on the linear feature of MRR events and randomization of limited trace orders of the input data. In practice, after linear-move-out (LMO) with an estimated dip, the input data are divided into several small windows to obtain a group of relatively horizontal MRR events. Then, these windows are randomized and filtered one by one. Due to the limited trace orders of each window, there are many possible rearrangements after randomization. Some rearrangements may lead to undesirable filtering performance. To obtain the rearrangements that lead to good filtering performance, each window's trace orders are randomly deranged by resampling from the input orders with uniform distribution. A 2-D synthetic data experiment shows the influence of different rearrangements on the filtering performance. Both 2-D synthetic data and 2-D field data demonstrate that the proposed method outperforms the 2-D FK filter to attenuate both aliased and nonaliased MRRs.

Frequency–Wavenumber (FK)-Based Data Selection in High-Frequency Passive Surface Wave Survey

Passive surface wave methods have gained much attention from geophysical and civil engineering communities because of the limited application of traditional seismic surveys in highly populated urban areas. Considering that they can provide high-frequency phase velocity information up to several tens of Hz, the active surface wave survey would be omitted and the amount of field work could be dramatically reduced. However, the measured dispersion energy image in the passive surface wave survey would usually be polluted by a type of “crossed” artifacts at high frequencies. It is common in the bidirectional noise distribution case with a linear receiver array deployed along roads or railways. We review several frequently used passive surface wave methods and derive the underlying physics for the existence of the “crossed” artifacts. We prove that the “crossed” artifacts would cross the true surface wave energy at fixed points in the f–v domain and propose a FK-based data selection technique to attenuate the artifacts in order to retrieve the high-frequency information. Numerical tests further demonstrate the existence of the “crossed” artifacts and indicate that the well-known wave field separation method, FK filter, does not work for the selection of directional noise data. Real-world applications manifest the feasibility of the proposed FK-based technique to improve passive surface wave methods by a priori data selection. Finally, we discuss the applicability of our approach.

Application of FK Filtering for Coherent Noise Removal in High Frequency Shallow Marine Data

The use of seismic reflection to study earth subsurface is commonly troubled by the presence of the coherent noise in the seismic data. This unwanted signal were generated by various sources and therefore had their own noise characteristic. The acquisition of the shallow marine seismic survey were done using a sparker source to obtain a high frequency seismic data. This however results in a stronger noise level in the recorded data. The application of FK filter were used to eliminate this unwanted noise using the data obtained from the Malacca Strait and Terengganu Bay. The result obtained prove to be successful in reducing the coherent noise while preserving the frequency content of the seismic data.

Combined adaptive multiple subtraction based on optimized event tracing and extended wiener filtering

The surface-related multiple elimination (SRME) method is based on feedback formulation and has become one of the most preferred multiple suppression methods used. However, some differences are apparent between the predicted multiples and those in the source seismic records, which may result in conventional adaptive multiple subtraction methods being barely able to effectively suppress multiples in actual production. This paper introduces a combined adaptive multiple attenuation method based on the optimized event tracing technique and extended Wiener filtering. The method firstly uses multiple records predicted by SRME to generate a multiple velocity spectrum, then separates the original record to an approximate primary record and an approximate multiple record by applying the optimized event tracing method and short-time window FK filtering method. After applying the extended Wiener filtering method, residual multiples in the approximate primary record can then be eliminated and the damaged primary can be restored from the approximate multiple record. This method combines the advantages of multiple elimination based on the optimized event tracing method and the extended Wiener filtering technique. It is an ideal method for suppressing typical hyperbolic and other types of multiples, with the advantage of minimizing damage of the primary. Synthetic and field data tests show that this method produces better multiple elimination results than the traditional multi-channel Wiener filter method and is more suitable for multiple elimination in complicated geological areas.

A PRELIMINARY STUDY OF SUBMARINE COLD SEEPS BY SEISMIC OCEANOGRAPHY TECHNIQUES

AbstractSubmarine cold seeps are widely distributed in the continental margin seas around the world. In this study, we apply a conventional multichannel seismic reflection (seismic oceanography) method to image the water column near the seafloor in order to detect cold seeps. In addition to analyzing the fluid escape structures, we also describe and discuss the development positions, seismic reflection characteristics as well as features of the cold seeps. The seismic reflection from the water column is very weak; therefore, the seismic sections above and below the seafloor are processed in two different sequences as follows: (1) geometry definition, direct wave attenuation and amplitude recovery, high‐pass filter, common midpoint sorting, constant velocity (seawater sound velocity) stack, and post‐stack FK filter in some sections; and (2) data quality control, amplitude recovery, 6∼100 Hz bandpass filter, multiple attenuation, deconvolution, velocity analysis, normal move‐out correction, common midpoint stack, post‐stack noise attenuation, 4∼70 Hz bandpass filter, and FX migration. The processed sections are then assembled together along the seafloor after carefully adjusting the color scale. The analysis shows that active cold seeps primarily present plume, broom, and/or irregular shapes that have weak and chaotic seismic reflections in the water column. The seismic reflection amplitude is enhanced at times; this could be attributed to the suspension of mud or particles in the water column. Cold seepage activities are typically associated with fluid escape structures, including mud diapirs, pipes, faults, fractures, gas chimneys, seabed pockmarks, and mud volcanoes. This indicates fluid migration from deep to shallow strata, fluid seepage or escape at the seafloor, as well as the formation of widespread cold seep activities. All the results herein are derived from a comprehensive interpretation of the seismic sections of the water columns and strata; however, further field studies, theoretical simulations, and experiments are required to confirm these conclusions.

Ground roll attenuation using SVD and time–frequency–wavenumber filters

Ground roll (GR) is a coherent noise phenomenon with high-amplitude and low-frequency patterns that conceal reflections. To create a correct velocity model, especially from medium to great depth, attenuation of the GR is unavoidable. To carry out attenuation and preserve a virgin data set, out of noise-cone singular value decomposition (SVD) and time–frequency–wavenumber (TFK) filters are used. Here four steps are introduced: (1) SVD, (2) FK filtering, (3) the Gabor transform (GT) and (4) a time-variant band-pass filter. SVD decomposes data into singular vectors and gives us the ability to have sub-images that relate to different singular values. The data set is reconstructed using first singular-vectors that relate to first singular-values, and include more signal and less noise. To preserve the reflection signal, the GR event is flattened using a forward normal move out correction (NMO) followed by the application of SVD to preserve 50% of the introduced events (to remove a part of the GR) and then finally reverse NMO is conducted. Although the FK filter is able to remove all of the GR energy based on the low velocity, the choice of low-dip for filtering causes high-amplitude smearing and distorts waveforms. Consequently, FK is applied to remove events with dips of more than 40 . The results of SVD plus high-dip FK have some issues that are created by merging high-amplitude and low-frequency events at the apex of the noise cone with reflections. Since at shallow depth and near offsets primary reflections have a higher frequency than the GR, the GT was used to deduce the dominant frequency of the GR for different times. Based on the estimated noise frequency, a cone area was chosen to filter the remaining noise and detect reflection events. These procedures were applied on real shot gathers to show the results of GR attenuation.

Near-surface fault detection by migrating back-scattered surface waves with and without velocity profiles

We demonstrate that diffraction stack migration can be used to discover the distribution of near-surface faults. The methodology is based on the assumption that near-surface faults generate detectable back-scattered surface waves from impinging surface waves. We first isolate the back-scattered surface waves by muting or FK filtering, and then migrate them by diffraction migration using the surface wave velocity as the migration velocity. Instead of summing events along trial quasi-hyperbolas, surface wave migration sums events along trial quasi-linear trajectories that correspond to the moveout of back-scattered surface waves. We have also proposed a natural migration method that utilizes the intrinsic traveltime property of the direct and the back-scattered waves at faults. For the synthetic data sets and the land data collected in Aqaba, where surface wave velocity has unexpected perturbations, we migrate the back-scattered surface waves with both predicted velocity profiles and natural Green's function without velocity information. Because the latter approach avoids the need for an accurate velocity model in event summation, both the prestack and stacked migration images show competitive quality. Results with both synthetic data and field records validate the feasibility of this method. We believe applying this method to global or passive seismic data can open new opportunities in unveiling tectonic features.

Iterative deblending using shaping regularization with a combined PNMO-MF-FK coherency filter

Simultaneous shooting achieves a much faster acquisition but poses a challenging problem for subsequent processing because of the interference from the neighbor crews. Separation of different sources, also called deblending, becomes important for the overall success of the new acquisition technology. In this paper, we propose a novel deblending approach following the shaping regularization framework. The shaping operator is chosen as an effective filter, combining pseudo normal-moveout, median filtering, and frequency wavenumber filtering (PNMO-MF-FK). We combine the median-filter based deblending approaches and the FK filter based deblending approach within the proposed framework. Instead of simply using the median filter to remove blending noise, we apply a pseudo NMO (PNMO) to prepare a relatively flatter profile in advance, which can make the median filter more effective. It is the first time that the PNMO, median filtering, and FK filtering are combined to form a powerful coherency filter in order to improve the performance of iterative deblending. The proposed deblending approach with the PNMO-MF-FK filter can obtain successful performance within small number of iterations. Compared with the alternative MF-FK filter and FK filter, the PNMO-MF-FK filter can obtain obviously better deblending results. We use both simulated synthetic and field data examples to demonstrate the performance of the proposed approach.

Impact of pulsed electric field and preheating on the lime purification of raw sugar beet expressed juices

This work discusses the effects of pulsed electric field (PEF) and preheating on the lime purification of raw sugar beet expressed juices. The PEF pre-treatment was applied to sugar beet cossettes before their pressing at 20°C with the PEF strength and duration of respectively E=600V/cm and tPEF=10ms. Alternatively, cossettes were preheated at 80°C for 10min before pressing to produce the thermal juice.A lime-carbonation process was applied for the purification of raw expressed juices. The influences of lime quantity (varied from 0 to 15kg/m3) on the filterability and the quality of juices were investigated. It was shown that the filtration kinetics of cold PEF juice is faster than that of thermal juice leading to lower values of filtration coefficient Fk and specific filter cake resistance α. Analysis showed that thin juices obtained after purification of PEF juices presents better qualitative characteristics than those obtained from thermal expressed juices. For instance, at the optimal lime quantity (10kg/m3), the purified PEF juice was less coloured (540 vs. 1360IU), less turbid and had less proteins and colloids leading to a higher juice purity (0.961 vs. 0.945) comparatively to the purified thermal juice.

Processing and interpretation of vintage 2D marine seismic data from the outer Hanö Bay area, Baltic Sea

A grid of previously unpublished, vintage 2D marine seismic lines has been processed and interpreted to the east of Hanö Bay, SW Baltic Sea. The 3200 km 2 study area lies on the transition between the Hanö Bay Basin to the West and Baltic Synelcise to the East, NE of the Tornquist intra shield tectonic zone. Data from the NA79, NA80 and RW84 surveys were selected for this study from the extensive Oljeprospektering AB (OPAB) Baltic Sea dataset. New processing workflows have been developed for the data which focus on suppressing two significant forms of noise, namely multiple and side scattered noise. Deconvolution in the tau-p domain, parabolic radon demultiple and post stack deconvolution are shown to be effective at attenuating multiple noise, while FK filtering in shot and receiver gathers is effective at removing side scattered noise. The newly processed data were interpreted and a series of maps detailing the structure of the basement, Cambrian and Silurian/Paleozoic horizons were constructed. These maps differ significantly to previously published interpretations of the area. Within the study area, a region of significant Late Carboniferous/Early Permian transtensional faulting and Late Cretaceous inversion is mapped in detail. This structure would have exhibited normal offsets of up to 600 m before inversion with later inverted displacements of up to approximately 200 m in places. This feature appears to extend some 20 km to the SW of the study area to the major fault bounding the Christiansø High. Based on the seismic interpretation, the area appears to have had a similar overall geological history as the adjacent Tornquist Zone to the SW. • A grid of 2D lines is processed and interpreted from the outer Hanö Bay area. • Key data issues are multiple and side scattered noise and large receiver spacing. • Parabolic radon demultiple, tau-p deconvolution and FK filtering are used. • A zone of major late Palaeozoic faulting and late Cretaceous inversion is mapped.

The use of F-K filter in the elimination of artefacts from a shallow seismic reflection data in Zaria, Nigeria

Near surface high resolution 2-D seismic reflection survey was carried out along the Zaria batholith. Zaria area forms part of the Precambrian basement complex of north central Nigeria which comprises Precambrian rocks made up of granite, gneiss and Low-grade metasediments. The granitic Zaria batholith intruded the gneiss and metasediments which forms the country rock. Reflection signals from shallow seismic survey in this area are often marred by surface waves, refraction and multiple reflections. The processing of the seismic data if not well handled often leads to migration artefacts which could be misconstrued as a seismic event. The field procedure employed for the geophysical survey was the split spread mode. The geophones were fixed at an interval of 1m, and a constant offset of 0.5 m. The common depth point method (CDP) with 12 fold coverage was adopted for the survey.Several artefacts were noticed on the result of the seismic migrated section, when the fk filter was initially applied only on the pre-stacked seismic data. The filtering and the common midpoint stacking could not completely eliminate the seismic noise on the pre-stacked seismic data. However, when an fk filter was applied on the post-stacked seismic section, the remaining seismic noise that survives the initial processing flow was eliminated. When migration was carried out on the filtered post-stack seismic section, the resulting seismic section was free from artefacts, andshowed clear seismic events.KEYWORDS: f-k filter, artefacts, shallow seismic, reflection, migration. Zaria

Feasibility of detecting near-surface feature with Rayleigh-wave diffraction

Detection of near-surfaces features such as voids and faults is challenging due to the complexity of near-surface materials and the limited resolution of geophysical methods. Although multichannel, high-frequency, surface-wave techniques can provide reliable shear (S)-wave velocities in different geological settings, they are not suitable for detecting voids directly based on anomalies of the S-wave velocity because of limitations on the resolution of S-wave velocity profiles inverted from surface-wave phase velocities. Therefore, we studied the feasibility of directly detecting near-surfaces features with surface-wave diffractions. Based on the properties of surface waves, we have derived a Rayleigh-wave diffraction traveltime equation. We also have solved the equation for the depth to the top of a void and an average velocity of Rayleigh waves. Using these equations, the depth to the top of a void/fault can be determined based on traveltime data from a diffraction curve. In practice, only two diffraction times are necessary to define the depth to the top of a void/fault and the average Rayleigh-wave velocity that generates the diffraction curve. We used four two-dimensional square voids to demonstrate the feasibility of detecting a void with Rayleigh-wave diffractions: a 2 m by 2 m with a depth to the top of the void of 2 m, 4 m by 4 m with a depth to the top of the void of 7 m, and 6 m by 6 m with depths to the top of the void 12 m and 17 m. We also modeled surface waves due to a vertical fault. Rayleigh-wave diffractions were recognizable for all these models after FK filtering was applied to the synthetic data. The Rayleigh-wave diffraction traveltime equation was verified by the modeled data. Modeling results suggested that FK filtering is critical to enhance diffracted surface waves. A real-world example is presented to show how to utilize the derived equation of surface-wave diffractions.

High-resolution coherent noise removal

In shallow hard water-bottom areas seismic data can be contaminated with linear refracted noise that may totally obscure signal amplitudes at medium and far offsets. Such noise is often highly aliased and resistant to removal via conventional approaches such as FK filtering or linear slant-stack. These can fail to remove the noise sufficiently for an accurate interpretation of amplitudes at far offsets, and have a tendency to smear signal amplitudes at all offsets.

SUMIC, a new strategic tool for exploration and reservoir mapping

We demonstrate that diffraction stack migration can be used to discover the distribution of near-surface faults. The methodology is based on the assumption that near-surface faults generate detectable back-scattered surface waves from impinging surface waves. We first isolate the back-scattered surface waves by muting or FK filtering, and then migrate them by diffraction migration using the surface wave velocity as the migration velocity. Instead of summing events along trial quasi-hyperbolas, surface wave migration sums events along trial quasi-linear trajectories that correspond to the moveout of back-scattered surface waves. We have also proposed a natural migration method that utilizes the intrinsic traveltime property of the direct and the back-scattered waves at faults. For the synthetic data sets and the land data collected in Aqaba, where surface wave velocity has unexpected perturbations, we migrate the back-scattered surface waves with both predicted velocity profiles and natural Green's function without velocity information. Because the latter approach avoids the need for an accurate velocity model in event summation, both the prestack and stacked migration images show competitive quality. Results with both synthetic data and field records validate the feasibility of this method. We believe applying this method to global or passive seismic data can open new opportunities in unveiling tectonic features.

Gathering good seismic data from the Otway Basin

Cultus Petroleum N.L. began exploration in petroleum permit EPP 23 of the offshore Otway Basin in December 1987. The permit was sparsely explored, containing only 2 wells and poor quality seismic data. A regional study was made taking into account the shape of the basin and the characteristics of the major seismic sequences. A prospective trend was recognised, running roughly parallel to the present shelf edge of South Australia. A new seismic survey was orientated over this prospective trend. The parameters were designed to investigate the structural control of the prospects in the basin. To improve productivity during the survey, north-south lines had to be repositioned due to excessive swell noise on the cable. The new line locations were kept in accordance with the structural model. Field displays of the raw 240 channel data gave encouraging results. Processing results showed this survey to be the best quality in the area. An FK filter was designed on the full 240 channel records. Prior to wavelet processing, an instrument dephase was used to remove any influence of the recording system on the phase of the data. Close liaison was kept with the processing centre over the selection of stacking velocities and their relevance to the geological model. DMO was found to greatly improve the resolution of steeply dipping events and is now considered to be part of the standard processing sequence for Otway Basin data. Seismic data of a high enough quality for structural and stratigraphic interpretation can be obtained from this basin.

The application of high resolution seismic processing to low relief structures – Harriet oil accumulation*

The Harriet structure is located within the offshore permit WA-192-P on the north-west shelf of Western Australia, near Barrow Island. The structure is a low-relief feature controlled by late faulting. An oil-bearing sand of Lower Cretaceous age forms the reservoir which has excellent porosity and permeability. The reservoir has a low seismic acoustic impedance contrast with the overlying deep marine shales. This low acoustic impedance contrast, combined with penetration problems due to near surface carbonates, results in a generally weak reflector at the top of the reservoir sands at a two-way time of approximately 1.5 s. Four recent vintages of seismic surveys using different recording parameters have been shot over the structure with a resultant grid spacing of 250 m. After the Harriet No. 1 discovery well, all the data over the structure were reprocessed using ‘state-of-the-art’ processing techniques to improve the resolution of the reflecting event at the top of the reservoir sand. The reprocessing was also carried out to minimize mis-ties between the various vintages of seismic data, and to improve the match between the surface seismic data and the vertical seismic profile at the wells. The above three aims were achieved by replacing standard pre-stack predictive deconvolution by deterministic deconvolution, i.e. instrument phase compensation and spectral equalization and by statistical wavelet extraction and shaping to ‘zero phase’. Also a pre-stack FK filter was applied to suppress noise on the data. Additionally, the application of spectral equalization to the suppression of low frequency short period multiples is demonstrated.