Land Seismic Data Research Articles

Effective parameters in ground roll attenuation using FO CRS stacking

Ground roll is a coherent noise in land seismic data that has high energy, high amplitude, low frequency and low velocity. It has to be attenuated in the seismic data processing as it may mask reflections in the zone of ground roll. In this study, we employed common reflection surface for finite offset (FO CRS) to attenuate the ground roll. The FO CRS stacking operator is a hyperbola; therefore, it fits the hyperbolic reflections in the prestack data. Conversely, the ground roll is linear in the common-midpoint (CMP) and common-shot (CS) gathers and can be distinguished and attenuated by the FO CRS operator. Thus, we search for the dip and curvature of the reflections in the CMP section and CS gather prior to the finite-offset section. When the algorithm is specified, the ground roll and reflections have low and high coherency values, respectively. So, any event with non-hyperbolic traveltime, like the linear traveltime ground roll can be removed.We applied the proposed method on a synthetic and an oilfield data from the west of Iran. Results showed that the FO CRS stacking method properly attenuated the ground roll. Further investigations were the effects of spatial aliasing, frequency content, random noise, ground roll dip, the range of dip and curvature scans and reflection amplitudes on ground roll attenuation by the FO CRS stacking. From mentioned parameters, spatial aliasing, frequency content, and random noise had no significant effects. On the contrary, the proposed method turned out to be strongly dependent upon ground roll dip, the range of dip and curvature scans and reflection amplitudes.

Near-surface imaging using ambient-noise body waves

We have introduced a workflow that allows subsurface imaging using upcoming body-wave arrivals extracted from ambient-noise land seismic data. Rather than using the conventional seismic interferometry approach based on correlation, we have developed a deconvolution technique to extract the earth response from the observed periodicity in the seismic traces. The technique consists of iteratively applying a gapped spiking deconvolution, providing multiple-free images with higher resolution than conventional correlation. We have validated the workflow for zero-offset traces with simple synthetic data and real data recorded during a small point-receiver land seismic survey.

Ground topography effects on near-surface elastic full waveform inversion

AbstractThe effects of neglecting ground surface topography variations in elastic full waveform inversion are investigated using two classes of synthetic example. The models include various high-contrast velocity and density anomalies, as they are often observed in near-surface applications. The first type of example shows that failing to account for even small amplitude fluctuations in topography introduces velocity artefacts in the near-surface part of the tomogram as well as degrades significantly the spatial resolution of features at greater depths. The disturbances are particularly severe when the topographic fluctuations have wavelengths comparable to the minimum seismic wavelength. The second type of synthetic example considers long wavelength topography variations of various amplitudes. It is found that neglecting topography with an amplitude fluctuation greater than half the minimum seismic wavelength leads to appreciable inversion image artefacts. Therefore, the incorporation of surface topography, even if it appears minor, is essential for successful elastic full waveform inversion of land seismic data.

Study on internal multiple elimination method on Land Seismic Data

SUMMARY Multiple is a tough issue in recent years, especially the internal multiples in deep earth. In this paper we proposed to construct virtual events to predict internal multiples. Then adopt the mean value multi-channel adaptive subtraction method for matching the multiple model and seismic data. However, the results depend on the parameters closely. We propose to apply the dynamic time wrapping method in order to accomplish the precise matching. And the regression of multiples can effectively improve the internal multiple elimination results when internal multiples are interfered with effective signal.

The impact of tilted geophones on land seismic data quality

The moving coil geophone is still the most commonly used sensor for land seismic surveys despite the introduction of other sensors. Modern geophone development has reached the stage where the signal recorded is of very high quality, but it can still be affected by the geophone being placed on an angle relative to the vertical ('tilt'). This paper describes the acquisition and analysis of field measurements using tilted geophones. It is shown that the critical angle of the 10 Hz geophones used for this test is 55°. For data recorded using vertically placed geophones separated by only 10 cm the perturbation level (the difference between the data recorded by adjacent geophones) averaged 8% and increased to more than 50% at tilt angles of 40o. The level of perturbation is heavily dependent on the orientation of the tilt angle relative to the source-detector axis, for example, for a geophone tilted at an angle of 30°, the perturbation varied between 14% and 48%. The obvious solution to these issues is to record data using sensors that have been planted extremely carefully or to use other sensors, such as digital accelerometers or 3C sensors that have the effect of tilt removed during processing.

Joining up land and marine seismic data: Case study from Procida and Ventotene Islands (Tyrrhenian Sea, Italy)

The seismic refraction survey, routinely used to obtain information on subsurface geology, has a limited use in the foreshore zone. We have evaluated a nonstandard approach to acquire seismic data in the backshore-foreshore area, joining up land and marine seismic data. The innovative part was the acquisition of a continuous seismic profile that allowed the recording of high-resolution data in a transition zone (TZ) to establish an integrated approach for improving the land-marine seismic model in areas characterized by a complex near surface geology. To achieve this objective, two seismic tests were carried out along the beaches of the Tyrrhenian islands of Procida and Ventotene. We defined the P-wave [Formula: see text] and S-wave velocities [Formula: see text] with depth by integrating the tomography of the refracted first arrivals ([Formula: see text] velocities versus depth) with the inversion of the phase velocities dispersion curves extracted from the surface waves (1D [Formula: see text] velocities models). Working with both seismic methods allowed us to overcame the limitations of each approach and to compare and check the obtained results. The velocity models enabled resolution of the near-surface velocity variations and definition of refractors down to a maximum depth of 40 m below ground level. This has provided useful insights to map the 2D bedrock surface and to evaluate ground stiffness and dynamic behavior of soil. Our study, aiming to demonstrate the feasibility of high-resolution seismic surveys in the land-sea TZ, proved that the use of a marine streamer connected to land cable, was a powerful tool to define different subsoil structures to assist with future planning (coastal management) of these areas.

Ground-Roll Noise Attenuation Using a Simple and Effective Approach Based on Local Band-Limited Orthogonalization

Bandpass filtering is a common way to estimate ground-roll noise on land seismic data, because of the relatively low-frequency content of ground roll. However, there is usually a frequency overlap between ground roll and the desired seismic reflections that prevents bandpass filtering alone from effectively removing ground roll without also harming the desired reflections. We apply a bandpass filter with a relatively high upper bound to provide an initial imperfect separation of ground roll and reflection signal. We then apply a technique called “local orthogonalization” to improve the separation. The procedure is easily implemented, since it involves only bandpass filtering and a regularized division of the initial signal and noise estimates. We demonstrate the effectiveness of the method on an open-source set of field data.

Application of waveform tomography to a crooked-line 2D land seismic data set

Onshore hydrocarbon exploration in the back-arc region of Japan suffers from seismic imaging challenges. Seismic data are typically acquired in a difficult environment: along a crooked line over a rough surface topography underlain by severe near-surface weathering layers. The area is geologically complex, and prestack depth processing is desirable. However, the data quality is suboptimal at near offsets, and it hinders the migration velocity analysis required for depth processing. Thus, a geologic interpretation needs to rely on time-processing results. Nevertheless, some data sets are rich in low-frequency components and contain clear refracted and wide-angle reflected waves, both of which are favorable conditions for the application of waveform tomography. We have used one such data set, and we determined the applicability of waveform tomography to estimate the P-wave velocity distribution. To mitigate difficulties in the data, we carefully optimized waveform tomography strategies and diligently validated the results. We evaluated the effects of the crooked line by conducting waveform tomography in 2D and 2.5D. We determined that for this data set, the effect of the crooked line was not substantial enough to require the 2.5D implementation, but it was large enough to require careful trace editing. We also minimized the effects of large variations in amplitudes due to near-surface effects and source and receiver characteristics, primarily by fitting phase components of the data during waveform tomography, but also by adjusting the amplitudes in a surface-consistent manner to stabilize the source estimation process. The final velocity model delineated known shallow sedimentary structures, but it also revealed deep large-thrust structures critical to the structural understanding of the area. The result confirmed the capability of waveform tomography to yield a reliable velocity model, and it also opened up the possibility of applications of depth processing in the region.

Suppression of near‐surface scattered body‐to‐surface waves: a steerable and nonlinear filtering approach

ABSTRACTWe present an approach based on local‐slope estimation for the separation of scattered surface waves from reflected body waves. The direct and scattered surface waves contain a significant amount of seismic energy. They present great challenges in land seismic data acquisition and processing, particularly in arid regions with complex near‐surface heterogeneities (e.g., dry river beds, wadis/large escarpments, and karst features). The near‐surface scattered body‐to‐surface waves, which have comparable amplitudes to reflections, can mask the seismic reflections. These difficulties, added to large amplitude direct and back‐scattered surface (Rayleigh) waves, create a major reduction in signal‐to‐noise ratio and degrade the final sub‐surface image quality. Removal of these waves can be difficult using conventional filtering methods, such as an filter, without distorting the reflected signal. The filtering algorithm we present is based on predicting the spatially varying slope of the noise, using steerable filters, and separating the signal and noise components by applying a directional nonlinear filter oriented toward the noise direction to predict the noise and then subtract it from the data. The slope estimation step using steerable filters is very efficient. It requires only a linear combination of a set of basis filters at fixed orientation to synthesize an image filtered at an arbitrary orientation. We apply our filtering approach to simulated data as well as to seismic data recorded in the field to suppress the scattered surface waves from reflected body waves, and we demonstrate its superiority over conventional techniques in signal preservation and noise suppression.

A study on the stationarity and Gaussianity of the background noise in land-seismic prospecting

In the denoising of seismic prospecting, background noise is often assumed to be stationary and Gaussian. However, this is not always appropriate for real seismic data. We used statistical tests to assess the stationarity and Gaussianity of land seismic data. The data we used for the analyses were passive noise records collected with receiver arrays in different land environments, e.g., deserts, steppes, and mountains. The results showed that the background noise was not strictly stationary, but locally stationary. The noise could be treated as a stationary series only in short time periods, whereas the stationarity became poor with increasing the time length of the noise records. By analyzing the behavior of noise data, we determined that the nonstationary noise always had more energy in the high-frequency band, which varied with the acquisition environments. The wind strength and the complexity of the environmental conditions also impacted the noise stationarity. Moreover, we found that noise in complex environments has a higher degree of Gaussianity than noise in simpler environment. Most of the noise records appeared to be a Gaussian process when examined over a period longer than 20 s, but they were found to be non-Gaussian when examined over shorter time periods of the order of 1 s.

Shearlet transform in aliased ground roll attenuation and its comparison with f-k filtering and curvelet transform

Ground roll, which is a Rayleigh surface wave that exists in land seismic data, may mask reflections. Sometimes ground roll is spatially aliased. Attenuation of aliased ground roll is of importance in seismic data processing. Different methods have been developed to attenuate ground roll. The shearlet transform is a directional and multidimensional transform that generates subimages of an input image in different directions and scales. Events with different dips are separated in these subimages. In this study, the shearlet transform is used to attenuate the aliased ground roll. To do this, a shot record is divided into several segments, and the appropriate mute zone is defined for all segments. The shearlet transform is applied to each segment. The subimages related to the non-aliased and aliased ground roll are identified by plotting the energy distributions of subimages with visual checking. Then, muting filters are used on selected subimages. The inverse shearlet transform is applied to the filtered segment. This procedure is repeated for all segments. Finally, all filtered segments are merged using the Hanning window. This method of aliased ground roll attenuation was tested on a synthetic dataset and a field shot record from the west of Iran. The synthetic shot record included strong aliased ground roll, whereas the field shot record did not. To produce the strong aliased ground roll on the field shot record, the data were resampled in the offset direction from 30 to 60 m. To show the performance of the shearlet transform in attenuating the aliased ground roll, we compared the shearlet transform with the f-k filtering and curvelet transform. We showed that the performance of the shearlet transform in the aliased ground roll attenuation is better than that of the f-k filtering and curvelet transform in both the synthetic and field shot records. However, when the dip and frequency content of the aliased ground roll are the same as the reflections, ability of the shearlet transform is limited in attenuating the aliased ground roll.

Modified surface boundary conditions for elastic waveform inversion of low-frequency wide-angle active land seismic data

Modified surface boundary conditions for elastic waveform inversion of low-frequency wide-angle active land seismic data

Six-component seismic land data acquired with geophones and rotation sensors: Wave-mode selectivity by application of multicomponent polarization filtering

Multicomponent acquisition systems today record incomplete data because they do not measure rotations. Geophones or accelerometers provide linear motion and hydrophones provide pressure, but no current commercial acquisition system includes sensors that measure rotations. Without rotations, the data provide incomplete recording of the wavefield because in three dimensions, there are six degrees of freedom — three linear displacements and three rotations. In two small 2D seismic surveys recorded with six components, three-component geophones were deployed and three-component rotation sensors that measured pitch, roll, and yaw were deployed. Pitch was measured independently with closely spaced geophones. Measuring rotations with closely spaced geophones is not practical in production, but it can be used in research and development to validate rotation-sensor data. A comparison of pitch measured by two independent methods finds that they fit after instrument designature. Data provided by rotation sensors have additional value because they can be used in analysis of singular value decomposition (SVD) to identify and separate ground roll and body waves.

Scattered ground‐roll attenuation using model‐driven interferometry

ABSTRACTScattered ground roll is a type of noise observed in land seismic data that can be particularly difficult to suppress. Typically, this type of noise cannot be removed using conventional velocity‐based filters. In this paper, we discuss a model‐driven form of seismic interferometry that allows suppression of scattered ground‐roll noise in land seismic data. The conventional cross‐correlate and stack interferometry approach results in scattered noise estimates between two receiver locations (i.e. as if one of the receivers had been replaced by a source). For noise suppression, this requires that each source we wish to attenuate the noise from is co‐located with a receiver. The model‐driven form differs, as the use of a simple model in place of one of the inputs for interferometry allows the scattered noise estimate to be made between a source and a receiver. This allows the method to be more flexible, as co‐location of sources and receivers is not required, and the method can be applied to data sets with a variety of different acquisition geometries. A simple plane‐wave model is used, allowing the method to remain relatively data driven, with weighting factors for the plane waves determined using a least‐squares solution. Using a number of both synthetic and real two‐dimensional (2D) and three‐dimensional (3D) land seismic data sets, we show that this model‐driven approach provides effective results, allowing suppression of scattered ground‐roll noise without having an adverse effect on the underlying signal.

Burying receivers for improved time‐lapse seismic repeatability: CO2CRC Otway field experiment

ABSTRACT4D seismic is widely used to remotely monitor fluid movement in subsurface reservoirs. This technique is especially effective offshore where high survey repeatability can be achieved. It comes as no surprise that the first 4D seismic that successfully monitored the CO2 sequestration process was recorded offshore in the Sleipner field, North Sea. In the case of land projects, poor repeatability of the land seismic data due to low S/N ratio often obscures the time‐lapse seismic signal. Hence for a successful on shore monitoring program improving seismic repeatability is essential.Stage 2 of the CO2CRC Otway project involves an injection of a small amount (around 15,000 tonnes) of CO2/CH4 gas mixture into a saline aquifer at a depth of approximately 1.5 km. Previous studies at this site showed that seismic repeatability is relatively low due to variations in weather conditions, near surface geology and farming activities. In order to improve time‐lapse seismic monitoring capabilities, a permanent receiver array can be utilised to improve signal to noise ratio and hence repeatability.A small‐scale trial of such an array was conducted at the Otway site in June 2012. A set of 25 geophones was installed in 3 m deep boreholes in parallel to the same number of surface geophones. In addition, four geophones were placed into boreholes of 1–12 m depth. In order to assess the gain in the signal‐to‐noise ratio and repeatability, both active and passive seismic surveys were carried out. The surveys were conducted in relatively poor weather conditions, with rain, strong wind and thunderstorms. With such an amplified background noise level, we found that the noise level for buried geophones is on average 20 dB lower compared to the surface geophones.The levels of repeatability for borehole geophones estimated around direct wave, reflected wave and ground roll are twice as high as for the surface geophones. Both borehole and surface geophones produce the best repeatability in the 30–90 Hz frequency range. The influence of burying depth on S/N ratio and repeatability shows that significant improvement in repeatability can be reached at a depth of 3 m. The level of repeatability remains relatively constant between 3 and 12 m depths.

Multidimensional interpolation using a model-constrained minimum weighted norm interpolation

Fourier-based minimum weighted norm interpolation (MWNI) has been widely used to regularize land seismic data. However, it has difficulty interpolating regular missing data that are spatially aliased. Minimizing the aliasing artifacts is still a technical challenge in MWNI. I have developed a novel method to address the aliasing problem in MWNI using a prior model as constraints. The prior model was constructed by a linear interpolation along dominant dips to produce a fully regular initial model. The spectral weights derived from this initial model are typically not aliased and can be used to constrain the least-squares inversion in MWNI, frequency by frequency, to overcome the aliasing artifacts. This new interpolation scheme expands the capability of conventional MWNI to handle spatially aliased data that are often associated with steeply dipping structures, and it reconstructs more reliable interpolation results. Decimation tests of a simple 2D synthetic data set and a complex 3D synthetic salt model revealed that model-constrained MWNI outperforms the conventional MWNI method in handling spatially aliased data. I applied this method to a land field data set and carried out a comprehensive evaluation of interpolated data through the processes of prestack analyses, prestack time migration, and prestack depth migration. The 5D interpolation successfully filled in missing data, increased spatial sampling of prestack gathers, and considerably improved migrated stacked images from the prestacked time and depth imaging.

Numerical modeling of elastic-wave scattering by near-surface heterogeneities

In land seismic data, scattering from surface and near-surface heterogeneities adds complexity to the recorded signal and masks weak primary reflections. To understand the effects of near-surface heterogeneities on seismic reflections, we simulated seismic-wave scattering from arbitrary-shaped, shallow, subsurface heterogeneities through the use of a perturbation method for elastic waves and finite-difference forward modeling. The near-surface scattered wavefield was modeled by looking at the difference between the calculated incident (i.e., in the absence of scatterers) and the total wavefields. Wave propagation was simulated for several earth models with different near-surface characteristics to isolate and quantify the influence of scattering on the quality of the seismic signal. The results indicated that the direct surface waves and the upgoing reflections were scattered by the near-surface heterogeneities. The scattering took place from body waves to surface waves and from surface waves to body waves. The scattered waves consisted mostly of body waves scattered to surface waves and were, generally, as large as, or larger than, the reflections. They often obscured weak primary reflections and could severely degrade the image quality. The results indicated that the scattered energy depended strongly on the properties of the shallow scatterers and increased with increasing impedance contrast, increasing size of the scatterers relative to the incident wavelength, decreasing depth of the scatterers, and increasing attenuation factor of the background medium. Also, sources deployed at depth generated weak surface waves, whereas deep receivers recorded weak surface and scattered body-to-surface waves. The analysis and quantified results helped in the understanding of the scattering mechanisms and, therefore, could lead to developing new acquisition and processing techniques to reduce the scattered surface wave and enhance the quality of the seismic image.

Separating the Near‐Surface Seismic Scattered Waves Using Seismic Interferometry Method

AbstractIt is important to separate the near‐surface seismic scattered waves from low signal‐noise data in mountain seismic exploration, and seismic interferometry is one of promising methods. The seismic interferometry representations of the near‐surface scattered wave are derived according to the seismic interferometry theory and the scattering theory. Those representations are composed of interferometry between actual wavefield and background wavefield and include cross‐correlation type and convolution type seismic interferometry expression. According to the near‐surface scattered wave separation theory and the geometry of land seismic exploration, the mixed configuration of convolution type and deconvolution type seismic interferometry is used. The application effect of the near‐surface scattered wave method is showed using the real land seismic data. The theoretical analysis and real data tests in gravel area indicate that the seismic interferometry method can separate not only scattered wave generated by scattering sources on survey lines, but also partial side scattered wave. The advantages of this technology are that it adapts to the uneven terrain and the complex near‐surface structure without information about topography and near‐surface velocity. In this article, the subtraction method of multi‐traces self‐adaptive matched filter is used to eliminate the near‐surface scattered wave from the real seismic data, and gets preferable results in gravel area.

Model‐based attenuation for scattered dispersive waves

ABSTRACTCoherent noise in land seismic data primarily consists in source‐generated surface‐wave modes. The component that is traditionally considered most relevant is the so‐called ground roll, consisting in surface‐wave modes propagating directly from sources to receivers.In many geological situations, near‑surface heterogeneities and discontinuities, as well as topography irregularities, diffract the surface waves and generate secondary events, which can heavily contaminate records.The diffracted and converted surface waves are often called scattered noise and can be a severe problem particularly in areas with shallow or outcropping hard lithological formations. Conventional noise attenuation techniques are not effective with scattering: they can usually address the tails but not the apices of the scattered events. Large source and receiver arrays can attenuate scattering but only in exchange for a compromise to signal fidelity and resolution.We present a model‑based technique for the scattering attenuation, based on the estimation of surface‐wave properties and on the prediction of surface waves with a complex path involving diffractions.The properties are estimated first, to produce surface‑consistent volumes of the propagation properties. Then, for all gathers to filter, we integrate the contributions of all possible diffractors, building a scattering model. The estimated scattered wavefield is then subtracted from the data. The method can work in different domains and copes with aliased surface waves. The benefits of the method are demonstrated with synthetic and real data.

Innovative Processing of 3D Land-Seismic Data

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 164016, ’Innovative Acquisition and Processing of Low Signal-to-Noise-Ratio 3D Land-Seismic Data Lead to a Leap in Subsurface Understanding: A Case History From Eastern Jordan,’ by Chris Pearse, Nicola Adams, Philip Bateman, Jack Bouska, Carlos Duque, Martyn Gravestock, and Johnathan Stone, BP, prepared for the 2013 SPE Middle East Unconventional Gas Conference and Exhibition, Muscat, Oman, 28-30 January. The paper has not been peer reviewed. The Risha concession, in the desert of eastern Jordan (bordering Iraq, Syria, and Saudi Arabia) contains the partially developed Risha gas field. This has historically been a poor-seismic-data- quality area, mostly because of a complex and variably karstified near-surface region. A high-density wide-azimuth (WAZ) acquisition was carried out in a timely and cost-efficient way, allowing insights into the area’s lithology and potential fracture distribution for the first time. Seismic Acquisition A limited exploration and appraisal license period of up to 5 years required that BP acquire 5000 km2 of 3D-seismic data—a very large survey by onshore standards—faster and more cost-effectively than ever before. These goals would mean that BP Jordan would have to achieve production rates and costs per area typical of marine-seismic surveys. The survey objective was to acquire a high-fold WAZ 3D survey suitable for structural interpretation, attribute analysis, and anisotropy studies. Data quality in Risha is affected by a complex near-surface region with significant karstification, causing a high degree of scattered noise that masks the primary reflection data. Previous 3D vintages were challenging to interpret; they failed to image the Ordovician reservoir adequately, were characterized by poor signal/noise ratio, and lacked resolution and continuity of key reflectors. To overcome the challenge, 3D-survey parameters were chosen to maximize both quality and productivity. To illuminate the subsurface with a high-fold WAZ ray-path distribution, the design used a 22-live-line recording patch, with 600-m receiver-line spacing. The nominal receiver line was 27.5 km long, resulting in 12,100 traces recorded with each vibrator point (VP), using an active spread spanning from 350 to more than 490 km2. The two-way time of the targets allowed for a relatively wide receiver- line spacing so that the recording patch could sample the entire reflected wave front. Use of single line roll ensured that 11 lines were active on either side of the source swath. Implementing a single roll maximizes both the geophysical quality and the line-crew efficiency, providing full azimuth sampling, maximum surface consistency for statics, and good line-crew efficiency. Receiver groups being spaced 50 m apart with a simple linear array of six geophones was intended to further assist line-crew productivity. Source lines were positioned 50 m apart, parallel to receiver lines with a 50-m VP interval, creating both long source lines to maximize vibrator efficiency and a fully sampled source grid (50×50 m) to attenuate scattered noise and create a high-fold data set.