Marine Vibrator Research Articles

Modeling acoustic wavefields from moving sources in the presence of a time-varying free surface

Marine vibrators are increasingly being recognized as a viable alternative to seismic airguns for ocean-bottom acquisition due to their ability to generate more low-frequency content and their less adverse impact on marine wildlife. However, their use introduces processing challenges, such as the Doppler effect and time-dependent source-receiver offsets, which are negligible in conventional airgun acquisition. In addition, the time-varying nature of the sea surface during the multisecond acquisition time introduces further challenges for processing and inversion. To accurately account for source motion and time-varying sea-surface effects in seismic data processing, we develop a reliable and robust numerical modeling tool. We use a mimetic finite-difference method in a generalized coordinate system to model the full acoustic wavefield triggered by a moving source in the presence of a time-varying sea surface. Our approach uses a time- and space-dependent coordinate transformation, which tracks the source movement and conforms to the irregular time-varying sea surface, to map an irregular physical domain in Cartesian coordinates to a regular computational domain in generalized coordinates. We formulate this coordinate transformation such that the coordinate systems conformally match below the ocean-bottom level. Numerical examples demonstrate that this approach is accurate and stable, even for an unrealistically exaggerated sea state. This computational tool is not limited to modeling but also could be used to develop advanced processing techniques for marine vibrator data, such as imaging and inversion.

Marine vibrator source motion correction for strictly monotonic sweeps

AbstractMarine vibrators represent an alternative seismic source technology that could come to market in the near future. A key challenge related to marine vibrator seismic data is the effect that phase dispersion from source motion has on the signal during transmission. As such, the recorded moving vibrator data will benefit from being phase corrected, so that the data appear as if they had been shot with a stationary source. This transformation is called the source motion correction. Previous source motion corrections used either specific dephasing operators for specific sweep types or pre‐correlation methods for any sweep type. A source motion correction dephasing operator has been derived, demonstrated and applied to real seismic data collected during a Marine Vibrator Joint Industry Project field trial of an array of marine vibrators. This dephasing operator has been made more general so that any strictly monotonic sweep through time may be used for this correction regardless of sweep type (e.g. linear or exponential). Moreover, the correction uses the pilot sweep as a direct input, measuring from it, the instantaneous frequency which can then be used to build the dephasing operator. This new more general form brings two key advantages over previous dephasing operator corrections: (1) Non‐analytically defined sweeps can now be source motion corrected, and (2) even when an analytically defined sweep (e.g. linear) is used, the transmitted sweep from the marine vibrator can vary from the theoretical input sweep; this correction can account for these changes. Furthermore, given that this source motion correction is a dephasing operator, it can be applied pre‐ or post‐correlation of the raw data with the pilot sweep, thus allowing greater flexibility in the processing. Lastly, some previously derived source motion corrections based on dephasing operators contained errors in their derivation; this new derivation addresses these errors resulting in an improved correction.

Technology Focus: Seismic (February 2024)

2023 wrapped up nicely with COP28 in Dubai. The key highlights were the commitments by both governments and the private sector to zero-methane production by 2030, net-zero greenhouse gas emissions from operations by 2050, and triple renewable power-generation capacity and double energy efficiency in this decade. There has been tremendous progress on our collective journey toward cleaner energy production, and now we must take it a notch higher. In the past couple of years, JPT’s Seismic feature has been marked by highly innovative seismic techniques and machine-learning work flows focused on reduction of carbon footprint; frontier exploration, expanding heartlands and brownfield development; and improved seismic survey, imaging, and attribute analysis for reservoir characterization and fracture diagnostics, which are in line with the COP28 pledges. This year’s feature is no different. Recent technical-paper titles have further shown the steady increase in the application of advanced seismic techniques and machine learning to mature “stranded” and “advantaged” hydrocarbon-bearing accumulations to production; improve carbon capture, storage, and leak detection; and analyze naturally and artificially induced fractured reservoirs and seismicity. The selected papers are reflective of these themes. In addition, some remarkable applications of seismic techniques are presented in the recommended papers. They include the following: - 2D nonlinear seismic site response analyses used to determine if the capacity of a silty sedimentation could support the load of a pipeline end termination in the event of an earthquake - The results of a pilot test of the Marine Vibrator, an industry-leading seismic-survey technique - High-resolution modeling to infer if an increase in seismicity is caused by an increase in pore pressure from wastewater injection in the Fort Worth Basin of north central Texas - 4D time/depth shifts and strain signals successfully used to estimate pressure depletion in the Gulf of Mexico Others are applying advanced measurement and modeling techniques to optimally place a long horizontal injector well in multilayered heterogeneous sandstone reservoirs and predicting reservoir presence from seismic velocity and pore-pressure prediction. These topics will supply the insights that will help us achieve the COP28 targets while we look forward to more exciting innovations in 2024. Recommended additional reading at OnePetro: www.onepetro.org. OTC 32267 Seismic Stability Assessment of a Mudmat on Liquefiable Seabed by Brian Carlton, Norwegian Geotechnical Institute, et al. OTC 32393 Predicting Reservoir Presence From Seismic Velocity Mapping and Pore-Pressure Prediction by Matthew James Legg, Shell OTC 32741 Marine Vibrator Milestone: A Pilot Seismic Survey by R. Alfaro, TotalEnergies, et al. SPE 212951 High-Resolution Modeling of Pore-Pressure Change, Fault Slip Potential, and Induced Seismicity in the Fort Worth Basin by Changqing Yao, Texas A&M University, et al. URTeC 3870451 Impact of Fracture Roughness on Fines Migration and Fracture-Aperture Growth in Calcareous Shale Rocks During Acidized Corefloods by Hasan J. Khan, King Fahd University of Petroleum and Minerals, et al.

Continuous sound from a marine vibrator causes behavioural responses of free-ranging, spawning Atlantic cod (Gadus morhua)

Marine vibrators are a new technology being developed for seismic surveys. These devices can transmit continuous instead of impulsive sound and operate over a narrower frequency band and at lower peak pressure than airguns, which is assumed to reduce their environmental impacts. We exposed spawning Atlantic cod (Gadus morhua) to sound produced by a prototype, but full-scale, marine vibrator, and monitored behavioural responses of tagged cod using acoustic telemetry. Fish were exposed to 10 × 3 h continuous sound treatments over a 4-day period using a randomised-block design. Sound exposure levels were comparable to airgun exposure experiments conducted previously with the same set-up ranging from ∼115 to 145 dB re 1 μPa2s during exposure. Telemetry data were used to assess 1) whether marine vibrator exposure displaced cod from the spawning ground, through estimation of residence and survival probabilities, and 2) fine-scale behavioural responses within the test site, namely swimming depth, activity levels, displacement, and home ranges. Forty-two spawning cod were tagged prior to the exposure, with 22 present during the exposure. All 22 tags were equipped with pressure sensors and ten of these additionally with accelerometers. While no premature departure from the spawning site was observed, cod reacted to the exposure by decreasing their activity levels (by up to 50%, SE = 7%) and increasing their swimming depth (by up to 2.5 m, SE = 1.0 m) within the test site during the exposure period. These behavioural responses varied by sex and time of day. Cod reactions to a marine vibrator may be more pronounced than reactions to airguns, possibly because continuous sound is more disturbing to fish than intermittent sound at the same exposure levels. However, given sample size limitations of the present study, further studies with continuous sound are necessary to fully understand its impact and biological significance.

A Deconvolution–Interpolation Method for Correction and De-Noising of Doppler-Shifted Marine Vibrator Data in the Frequency–Wavenumber Domain

A Deconvolution–Interpolation Method for Correction and De-Noising of Doppler-Shifted Marine Vibrator Data in the Frequency–Wavenumber Domain

3-D curvelet-based WPOCS reconstruction, Doppler-shift correction, and noise attenuation of jittered sampled marine vibrator data

3-D curvelet-based WPOCS reconstruction, Doppler-shift correction, and noise attenuation of jittered sampled marine vibrator data

Modeling the seismic wavefield of moving marine vibrator source

Marine vibrators are an emerging alternative to conventional air guns in ocean-bottom acquisition due to their ability to generate low-frequency waves and limited adverse impact on marine wildlife. However, using marine vibrators introduces challenges not found in conventional air-gun-based acquisition where receivers are placed on the ocean bottom, including handling the phenomena associated with the Doppler effect and time-dependent source-receiver offsets due to the source motion. Standard seismic data processing solutions assume stationary sources and receivers for the duration of any seismic experiment (e.g., a shot); however, accurately accounting for source motion effects in processing is critical for optimal subsurface imaging. To address these challenges, we develop a finite-difference approach for modeling the full acoustic wavefield in a generalized coordinate system that tracks a moving source. Synthetic examples demonstrate that this technique accurately and stably models high-velocity moving sources and accurately accounts for the wavefield distortion predicted by the Doppler effect. This approach is not limited to modeling wavefield propagation for a moving source and can be used to develop advanced imaging and inversion techniques (e.g., reverse time migration and full waveform inversion) for data acquired using marine vibrators. In addition, the developed approach is not only limited to modeling mobile sources but also can model conventional towed-streamer data.

The music of marine seismic: A marine vibrator system based on folded surfaces

Marine vibrators have bespoke geophysical benefits that are yet to be harnessed because of robustness and efficiency issues. We have developed a new marine vibrator source technology that is efficient and stable. The source technology overcomes the historical problems of inefficiency and robustness by using folded surface technology and resonance frequency tuning. We show measured output examples that demonstrate that the folded surface concept combined with small displacements can provide the required output levels. Our source system consists of a low-frequency module covering 1–10 Hz and a high-frequency module covering 10–125 Hz. The source control system has shown high stability and precision and can handle harmonic distortion. With the aid of synthetic data examples, we demonstrate that seismic data acquired using marine vibrators in either intermittent or continuous mode can be processed. Finally, we demonstrate the environmental friendliness of the source in comparison to air gun-based sources.

Advances in marine vibrators for seismic survey

The reducing impact of noise from traditional air-guns on marine mammals is an actual problem for oil and gas producers. The application of coherent, broadband signals instead of explosive, high intensity, and air-gun pulses is the potential way of noise mitigation. The three major oil companies, Shell, Exxon, and Total, are sponsoring the Marine Vibrator Joint Industry Project MVJIP. Marine Vibrators are a coherent type of seismic source, which are less harmful for marine inhabitants and give a clearer, higher resolution imaging of the sub-bottom formations. Teledyne as one of the participants in the MVJIP using a large underwater bubble resonator as a new type of seismic source. The cylindrical bubble keeps its shape in the water and can be towed with the speed 8 knots. The polyurethane membrane covering the gas-filled bubble supports a high volume displacement. The research shows that the best driver for ultra-low frequency 1–10 Hz source is the blower with the airflow controlled by a proportion valves. The experimental prototype has good performance with a maximum more than SPL 200 dB at the frequency 5–12 Hz. However, for a limited sound pressure level of 185 dB in a frequency band of 10–100 Hz, the subwoofer driver shows very good performance.

The shape of things to come — Development and testing of a new marine vibrator source

Ten years ago, CGG launched a project to develop a new concept of marine vibrator (MV) technology. We present our work, concluding with the successful acquisition of a seismic image using an ocean-bottom-node 2D survey. The expectation for MV technology is that it could reduce ocean exposure to seismic source sound, enable new acquisition solutions, and improve seismic data quality. After consideration of our objectives in terms of imaging, productivity, acoustic efficiency, and operational risk, we developed two spectrally complementary prototypes to cover the seismic bandwidth. In practice, an array composed of several MV units is needed for images of comparable quality to those produced from air-gun data sets. Because coupling to the water is invariant, MV signals tend to be repeatable. Since far-field pressure is directly proportional to piston volumetric acceleration, the far-field radiation can be well controlled through accurate piston motion control. These features allow us to shape signals to match precisely a desired spectrum while observing equipment constraints. Over the last few years, an intensive validation process was conducted at our dedicated test facility. The MV units were exposed to 2000 hours of in-sea testing with only minor technical issues.

Marine vibrators: the new phase of seismic exploration

ABSTRACTMarine seismic vibrators are generally considered to be less intrusive than airguns from an environmental perspective. This is because they emit their energy spread out in time, rather than in a single, high‐intensity pulse. There are also significant geophysical benefits associated with marine vibrators, and they stem from the ability to specify in detail the output acoustic waveform. The phase can be specified independently at each frequency. Such detailed control cannot be achieved with conventional airgun sources, where the phase can only be modified using simple overall time delays. The vibrator phase can be employed in several different ways: it can be applied to the overall source phase in a sequence so that it varies from one source point to the next; it can be applied to the individual vibrators within the source array so the source directivity is changed; it can be applied to the overall source phase of each source in a simultaneous source acquisition. Carefully designed phase sequences can attenuate the residual source noise, and this in turn allows extra source points to be interleaved between the conventional ones. For these extra source points, the relative phase of the vibrators within the array can be chosen to create a transverse gradient source, which illuminates the earth predominantly in directions out of the plane of the sail line without left/right ambiguity. If seismic vibrator data are acquired using interleaved conventional and transverse gradient sweeps, more information is collected per kilometre of vessel travel than is the case in conventional acquisition. This richer data acquisition leads to the possibility of acquiring all the necessary seismic data in a shorter time. Three‐dimensional reconstruction techniques are used to recover the same image quality that would have been obtained using the conventional, more time‐consuming acquisition. For a marine vibrator to be suitable for these techniques it must, in general terms, have ‘high fidelity’. The precise device specifications are defined through realistic end‐to‐end simulations of the physical systems and the processing. The specifications are somewhat more onerous than for a conventional vibrator, but they are achievable. A prototype vibrator that satisfies these requirements has been built. In a simulated case study of a three‐dimensional deep‐water ocean bottom node survey, the seismic data could have been acquired using marine vibrators in one third of the time that it would have taken using airguns.

Latest field trial confirms potential of new seismic method based on continuous source and receiver wavefields

eSeismic is a novel seismic methodology based on the emission and recording of continuous source and receiver wavefields. One of the motivations behind developing the methodology has been the increased focus on the potential environmental impact of marine seismic acquisition, which the new methodology seeks to reduce. A particular focus has been placed on the peak sound pressure levels emitted from seismic sources and their potential impact on marine mammals and fish with swim bladders. Consequently, authorities across the world have started to introduce stronger regulations concerning the use of seismic sources. The industry has responded by engaging in the development of marine vibrator systems that emit lower-amplitude transient signals and hence are expected to comply with stricter environmental regulations. Different marine vibrator systems are currently being developed or tested but none have reached full-scale commercial readiness. The methodology described in this paper has not been developed with any specific marine source technology in mind. The desired signal for the outlined methodology is that of white noise, as this enables deconvolution of the data with the total source wavefield. Indeed any type of mechanical device that produces a source signal that approaches the properties of white noise can be utilized in the eSeismic method. As described later, existing air gun equipment used on board modern seismic vessels has been used to generate the results discussed here and is equally suited for this method as are any marine vibrator systems of the future.

The Marine Vibrator Joint Industry Project: four years on

The Marine Vibrator Joint Industry Project (MVJIP), sponsored by Shell, Total and ExxonMobil, has been ongoing for four years. During this time significant progress has been made towards developing fully commercial marine vibrators. We begin by describing the history of, and need for, marine vibrator development, including the successes and shortcomings of the technology development before the MVJIP. Following this, we discuss the motivation for initiating the MVJIP, including the specifications required and initial phases of the project. Next, we move on to the vendors that are developing the different options. For each of the three vendors, we shall discuss their background with the technology, the type of technology being developed and their results to date. After discussing the vendors, we shall move on to the impact the MVJIP has had on the commercial marine vibrator industry. Finally, we will discuss our experiences to date and conclude with further work and the way forward for the project.

Underwater bubble low frequency source for Arctic acoustic tomography, navigation, and communication

Arctic acoustic tomography requires a broadband source in the frequency range of 5–100 Hz. To meet this requirement, Teledyne Marine suggests applying a seismic source, recently developed for the Marine Vibrator Joint Industry Project. The source is considered to be less harmful for marine inhabitants and gives more precise and higher resolution imaging of the subsurface formations and structures. The coherent source is based on the application of an underwater, gas filled bubble resonator covered by an elastic membrane. The membrane supports high volume displacement. The sources are not sensitive to cavitation and to coupling effects. The fluid dynamics and acoustics of a spherical resonator are defined by the Rayleigh-Plesset equation. The buoyancy deforms the shape of a real bubble from spherical. The 3D simulation and experiments have shown that a cylindrical form is a practical engineering solution. It performances similar to a spherical bubble, keeps its shape and can be towed with a high speed. The Q-factor of a practical bubble resonator is ~10. Two systems are considered to cover a wide frequency band: a tunable resonator and a broadband multi-resonance system. The research proved that the bubble sound source is a practical solution for a frequency below 100 Hz.

A comparison of random and periodic marine simultaneous-source encoding

Separation algorithms for marine simultaneous-source data generally require encoded sources. Proposed encoding schemes include random time delays (time dithers), periodic time sequences (such as those referred to as seismic apparition), and periodic phase sequences (for sources with fully controlled phase like a marine vibrator). At a given frequency, time dithers spread energy at a given wavenumber over all wavenumbers, phase sequences shift the energy by a fixed wavenumber (independent of frequency), and time sequences split energy over multiple wavenumbers in a frequency-dependent way. The way the encoding scheme distributes energy in the wavenumber domain is important because separation algorithms generally assume that, in the absence of encoding, all energy falls into the signal cone. Time dithering allows separation by inversion. At low frequencies, the inverse problem is overdetermined and easily solved. At higher frequencies, sparse inversion works well, provided the data exhibit a sufficiently sparse representation (consistent with compressive sensing theory). Phase sequencing naturally separates the sources in the wavenumber domain at low frequencies. At higher frequencies, ambiguities must be resolved using assumptions such as limited dispersion and limited complexity. Time sequencing allows a simple separation at low frequencies based on a scaling and subtraction process in the wavenumber domain. However, the scaling becomes unstable near notch frequencies, including DC. At higher frequencies, a similar problem to that for phase sequencing must be solved. The encoding schemes, therefore, have similar overall properties and require similar assumptions, but differ in some potentially important details. Phase sequencing is clearly only applicable to phase-controllable sources, and the different encoding schemes have other implications for data acquisition, for example, with respect to operational complexity, efficiency, spatial sampling, and tolerance to errors.

Offshore Seismic Feeling Pressures to Change

Seismic surveys are created using bursts of acoustic energy that are referred to as “marine sound, or noise, depending on your perspective.” With that thought, John Young, director of the sound business line for CSA Ocean Sciences, introduced a recent panel discussion that included seismic innovators working on new sound sources designed to produce better subsurface images as well as scientists and regulators concerned about the environmental impact of that noise. At that session and others at the recent annual meeting of the Society of Exploration Geophysicists (SEG), there was discussion about multiple ways to move away from the intense pulses of acoustic energy produced by air guns. The industry standard emits both useful sound for seismic imaging and higher-frequency noise that dissipates in the ground. One sign that this talk may lead to alternatives to air guns for marine seismic is a joint industry project by three major oil companies backing a new generation of offshore seismic sound sources designed to reduce noise and improve the seismic signal. Their goal is to “de-risk” vibrator technology, said Mike Jenkerson, geophysical advisor for marine seismic at Exxon Mobil, who represented the Marine Vibrator Joint Industry Project ( JIP) at the conference. The JIP managed by Texas A&M University is supporting development and testing to determine if there is an alternative to air guns that is effective and reliable even with a smaller acoustic signal. The signal is the critical difference between sounds created using controlled vibrations and air guns, which are called impulsive sound sources and create loud, sharp booms as a large volume of air is emitted. Marine science and regulatory experts on the SEG panel indicated that research on the impact of subsea noise on sea life is likely to gradually lead to increasing limits on seismic surveys, where noise regulation is already a costly fact of life.

Frequency-domain iterative learning control of a marine vibrator

To the purpose of marine seismic acquisition, new acoustic sources have been developed to reduce the environmental impact. The use of marine vibrators makes it possible to define emission frequency ranges, consequently allowing limitation of the frequencies that disturb marine animal life. Constructing marine vibrators with high efficiency and linear dynamics is however difficult, and the vibrators suffer from both friction, backlash and high-order harmonics. These nonlinear effects, in combination with drifting dynamics, make the required control a crucial and challenging problem. This paper presents a model-based iterative learning control solution, performed in the frequency-domain. Additionally, an adaptive reidentification algorithm is developed to cope with drifting dynamics. The proposed solutions are successfully evaluated in experiments with a marine vibrator.

Method of seismic surveying, a marine vibrator arrangement, and a method of calculating the depths of seismic sources

A method of seismic surveying comprises emitting seismic energy at two or more different depths during a sweep. In one embodiment, the depth of a seismic source is varied during a sweep, by raising or lower the source while it is emitting seismic energy. In another embodiment, an array of two or more marine vibrators is used as the source of seismic energy, with the vibrators in the array being disposed at different depths. The invention allows notch frequencies in the amplitude spectrum to be eliminated, and allows improvements in both the spectral flatness and the amplitude at low frequencies.

An electrical marine vibrator with a flextensional shell

A completely new electro-mechanical marine Vibroseis concept is introduced that uses a flextensional shell with a uniquely developed form. Two controllable output resonances achieve a very high efficiency and repeatability, with a typical frequency bandwidth of 6-100 Hz. The marine vibrator can be used as a standard towed acoustic source in shallow water, or as a stationary source in transition zone environments. It is particularly significant that the vibrator requires only an electrical power supply, cannot leak hydraulic fluids, is easily transported, and is suitable for applications requiring very low environmental impact. A marine vibrator will provide several environmental advantages. Vibrator technology spreads the net source energy over a long period, reducing the acoustic power in comparison to impulsive sources. This is attractive for applications where high peak power may be problematic. This fact was established by the original hydraulic vibrators developed previously. An electrical marine vibrator offers even more advantages than hydraulic vibrators. There is no need for heavy equipment and hydraulic systems that can cause hydraulic oil spills. As the electrical vibrator requires only an electrical power supply it can be easily transported to different vessels and locations without any costly installations and potential environmental hazards. The marine vibrators discussed here have been tested as a standard towed acoustic source in shallow water, and as a stationary source in transition zone environments (4-6 ft of water). These applications are particularly well suited for this type of source.

An electrical marine vibrator with a flextensional shell: DECEMBER 2005 DRAFT

A completely new electro-mechanical marine vibroseis concept is introduced that uses a flextensional shell with a uniquely developed form. Two controllable output resonances achieve a very high efficiency and repeatability, with a typical frequency bandwidth of 6 - 100 Hz. The marine vibrator can be used as a standard towed acoustic source in shallow water or as a stationary source in transition zone environments. Of particular significance, the vibrator requires only an electrical power supply, cannot leak hydraulic fluids, is easily transported, and is suitable for applications requiring very low environmental impact.