Marine Streamer Research Articles

Crossline wavefield reconstruction from multicomponent streamer data: Part 2 — Joint interpolation and 3D up/down separation by generalized matching pursuit

Computation of the 3D upgoing/downgoing separated wavefield at any desired position within a marine streamer spread is enabled by multicomponent streamers that can measure the crossline and vertical components of water-particle motion in addition to the pressure. We introduce the concept of simultaneous interpolation and deghosting and describe a new technique, generalized matching pursuit (GMP), to achieve this. This method is based on the matching-pursuit technique and iteratively reconstructs the signal as a combination of optimal basis functions. In the GMP method, the basis functions describing the unknown 3D upgoing wavefield are filtered by appropriate forward ghost operators before being matched to the multicomponent measurements. As a data-dependent method, GMP can operate on data samples that are highly aliased in the crossline direction without relying on assumptions about seismic events such as linearity. The technique is naturally suitable for data with only a small number of samples that may be irregularly spaced. We demonstrate the efficacy and robustness of the GMP method on several synthetic data sets of increasing complexity and in the presence of noise.

Elastic full waveform inversion of multicomponent ocean-bottom cable seismic data: Application to Alba Field, U. K. North Sea

Elastic full waveform inversion of multichannel seismic data represents a data-driven form of analysis leading to direct quantification of the subsurface elastic parameters in the depth domain. Previous studies have focused on marine streamer data using acoustic or elastic inversion schemes for the inversion of P-wave data. In this paper, P- and S-wave velocities are inverted for using wide-angle multicomponent ocean-bottom cable (OBC) seismic data. Inversion is undertaken using a two-dimensional elastic algorithm operating in the time domain, which allows accurate modeling and inversion of the full elastic wavefield, including P- and mode-converted PS-waves and their respective amplitude variation with offset (AVO) responses. Results are presented from the application of this technique to an OBC seismic data set from the Alba Field, North Sea. After building an initial velocity model and extracting a seismic wavelet, the data are inverted instages. In the first stage, the intermediate wavelength P-wave velocity structure is recovered from the wide-angle data and then the short-scale detail from near-offset data using P-wave data on the [Formula: see text] (vertical geophone) component. In the second stage, intermediate wavelengths of S-wave velocity are inverted for, which exploits the information captured in the P-wave’s elastic AVO response. In the third stage, the earlier models are built on to invert mode-converted PS-wave events on the [Formula: see text] (horizontal geophone) component for S-wave velocity, targeting first shallow and then deeper structure. Inversion of [Formula: see text] alone has been able to delineate the Alba Field in P- and S-wave velocity, with the main field and outlier sands visible on the 2D results. Inversion of PS-wave data has demonstrated the potential of using converted waves to resolve shorter wavelength detail. Even at the low frequencies [Formula: see text] inverted here, improved spatial resolution was obtained by inverting S-wave data compared with P-wave data inversion results.

General surface multiple prediction: a flexible 3D SRME algorithm

Ideal 3D SRME (surface-related multiple elimination) has geometric requirements for its input data that are not met by marine streamer surveys. Ian Moore and Bill Dragoset offer a solution supported by field data examples which uses a modified algorithm based on a multidimensional nearest-neighbour search to find recorded traces that are closest, in a Euclidian sense, to the desired traces demanded by ideal 3D SRME.

First look at seismic data from a towed dual-sensor streamer

A pressure sensor in a towed streamer always records two wavefields that interfere with each other. The two wavefields are the upgoing pressure wavefield propagating directly to the pressure sensor from the Earth below, and the downgoing pressure wavefield reflected downwards from the free (sea) surface immediately above the streamer. Thus, every reflection wavelet recorded by conventional marine streamers is accompanied by a “ghost” reflection from the ocean's surface. The reflection wavelet is undesirably elongated, reducing temporal resolution. The consequence, as illustrated on the left of Figure 1, is that a series of receiver ghost notches is introduced into the frequency spectra. There has historically been a forced trade-off between towing shallow to record high-frequency (but noisy) data at the cost of reduced lower frequencies, or towing deep to record low frequencies at the cost of reduced higher frequencies.

A wide-azimuth streamer acquisition pilot project in the Gulf of Mexico

A 3D wide-azimuth (WAZ) marine streamer survey was designed to image deep objectives below a complex salt structure in a deepwater area of the Gulf of Mexico. Numerous technical and logistical challenges were considered in developing the design for this survey. The final candidate designs were tested with synthetic data modeling and imaging. The final selected wide-azimuth design was used for a survey acquired over the Friesian prospect in the Gulf of Mexico. We present some of the modeling studies supporting the wide-azimuth survey design, as well as acquisition and processing results from the Friesian WAZ pilot project.

Fourier reconstruction of marine-streamer data in four spatial coordinates

Many methods exist for interpolation of seismic data in one and two spatial dimensions, but few can interpolate properly in three or four spatial dimensions. Marine multi-streamer data typically are sampled relatively well in the midpoint and absolute offset coordinates but not in the azimuth because the crossline shot coordinate is significantly under sampled. We approach the problem of interpolation of marine-streamer data in four spatial dimensions by splitting the problem into a 1D interpolation along the densely sampled streamers and a 3D Fourier reconstruction for the remaining spatial coordinates. In Fourier reconstruction, the Fourier coefficients that synthesize the nonuniformly sampled seismic data are estimated in a least-squares inversion. The method is computationally efficient, requires no subsurface information, and can handle uniform grids with missing data as well as nonuniform grids or random sampling. The output grid of the 1D interpolation in the first step is arbitrary. When the output grid has uniform inline midpoints spacing, the 3D Fourier reconstruction in the second step is performed in the crossline midpoint, absolute offset, and azimuth coordinates. When the first step outputs to uniform absolute offset, the 3D Fourier reconstruction handles the crossline/inline midpoint and the azimuth coordinates. In both cases, the main innovation is the inclusion of the azimuthal coordinate in the Fourier reconstruction. The azimuth multiplicity must be increased for the method to be successful, which means that overlap shooting is required. We have tested the algorithm on synthetic streamer data for which the proposed method outperforms an approach where the azimuthal coordinate is ignored. Potential applications are interpolation of marine streamer data to decrease the crossline source sampling for the benefit of 3D multiple prediction and regularization to reduce sampling-related differences in processing of time-lapse data.

On “Delayed-shot 3D depth migration” ()

We present an alternative perspective on a key equation in the paper “Delayed-shot 3D depth migration” by Zhang et al. (2005). An alternative perspective indicates that a greater number of P-values are needed for a complete delayed-shot migration of typical marine-streamer data than those presented by Zhang et al. With the alternative equation, delayed-shot WEM migration is mathematically no more efficient than shot-WEM migration for typical marine streamer data.

Delayed-shot 3D depth migration

For 3D seismic imaging in structurally complex areas, the use of migration by wavefield extrapolation has become widespread. By its very nature, this family of migration methods operates on data sets that satisfy a wave equation in the context of a single, physically realizable field experiment, such as a common-shot record. However, common-shot migration of data recorded over dipping structures requires a migration aperture much larger than the recording aperture, resulting in extra computations. A different type of wave-equation record, the response to a linear or planar source, can be synthesized from all the common-shot records. Synthesizing these records from common-shot records involves slant-stack processing, or applying delays to the various shots; we call these records delayed-shot records. Delayed-shot records don't suffer from the aperture problems of common-shot records since their recording aperture is the length of the seismic survey. Consequently, delayed-shot records hold potential for efficient, accurate imaging by wavefield extrapolation. We present a formulation of delayed-shot migration in 2D and 3D (linear sources) and its application to 3D marine streamer data. This formulation includes a discussion of sampling theory issues associated with the formation of delayed-shot records. For typical marine data, 2D and 3D delayed-shot migration can be significantly more efficient than common-shot migration. Synthetic and real data examples show that delayed-shot migration produces images comparable to those from common-shot migration.

4D Ocean Bottom Seismic technology: an innovative tool for improved hydrocarbon recovery at Gullfaks

The Gullfaks Oil Field is located in the Norwegian sector of the Northern North Sea. Time-lapse (4D) seismic data have been used at Gullfaks since 1995 and have contributed significantly to the reservoir management of the field. Permanent field installations limit the area where new marine streamer surveys can be acquired; this restriction affects in 25% of the field. In 2001 an Ocean Bottom Seismic (OBS) pilot survey was acquired around the Gullfaks C (GFC) platform, to test whether the OBS technology could cover the ‘shadow zones’ around the permanent installations. The results from the 2001 OBS survey clearly show that the OBS data cover the ‘shadow zone’ and provide new 4D information around the GFC platform. Within the OBS area two new wells have been successfully drilled based on updated 4D information comparing streamer data from 1999 and OBS data from 2001. Based on the experience from the 2001 survey a new OBS survey was acquired in 2003 to cover the areas around the GFA and GFB platforms.

High-resolution seismic reflection surveying at paved areas using an S-wave type Land Streamer

High-resolution S-wave reflection surveying has been successfully conducted on paved areas using a Land Streamer originally designed by the author. The main feature of the Land Streamer tool is the non-stretch woven belt on which geophone units are mounted to form a multichannel geophone array similar to a marine streamer. Because it is easily towed by a vehicle or by hand, the tool leads to high performance in field measurements and resultant cost-effectiveness of high-resolution reflection surveys. Although each geophone unit is coupled to the pavement through a metallic baseplate instead of being firmly planted in the ground, the Land Streamer tool provides comparatively clean data, unaffected by traffic noise even on the pavement. Thus, the tool is capable of expanding the opportunity for S-wave reflection surveys in urban areas where many surfaces are paved and traffic noise is severe.A series of high-resolution S-wave reflection surveys on paved areas delineated detailed structures of surface layers shallower than 60 m, and proved the wide applicability of the tool to engineering, environmental applications, and earthquake disaster prevention projects.

Offset‐domain pseudoscreen prestack depth migration

The double square root equation for laterally varying media in midpoint‐offset coordinates provides a convenient framework for developing efficient 3‐D prestack wave‐equation depth migrations with screen propagators. Offset‐domain pseudoscreen prestack depth migration downward continues the source and receiver wavefields simultaneously in midpoint‐offset coordinates. Wavefield extrapolation is performed with a wavenumber‐domain phase shift in a constant background medium followed by a phase correction in the space domain that accommodates smooth lateral velocity variations. An extra wide‐angle compensation term is also applied to enhance steep dips in the presence of strong velocity contrasts. The algorithm is implemented using fast Fourier transforms and tri‐diagonal matrix solvers, resulting in a computationally efficient implementation. Combined with the common‐azimuth approximation, 3‐D pseudoscreen migration provides a fast wavefield extrapolation for 3‐D marine streamer data. Migration of the 2‐D Marmousi model shows that offset domain pseudoscreen migration provides a significant improvement over first‐arrival Kirchhoff migration for steeply dipping events in strong contrast heterogeneous media. For the 3‐D SEG‐EAGE C3 Narrow Angle synthetic dataset, image quality from offset‐domain pseudoscreen migration is comparable to shot‐record finite‐difference migration results, but with computation times more than 100 times faster for full aperture imaging of the same data volume.

A proposed polarity standard for multicomponent seismic data

This paper proposes a multicomponent acquisition and preprocessing polarity standard that will apply generally to the three Cartesian geophone components and the hydrophone or microphone components of a 2‐D or 3‐D multicomponent survey on land, at the sea bottom, acquired as a vertical seismic profile, vertical‐cable, or marine streamer survey. We use a four‐component ocean‐bottom data set for purposes of illustration and example. A primary objective is a consistent system of polarity specifications to facilitate consistent horizon correlation among multicomponent data sets and enable determination of correct reflectivity polarity.The basis of this standard is the current SEG polarity standard, first enunciated as a field‐recording standard for vertical geophone data and hydrophone streamer data. It is founded on a right‐handed coordinate system: z positive downward; x positive in the forward line direction in a 2‐D survey, or a specified direction in a 3‐D survey, usually that of the receiver‐cable lines; and y positive in the direction 90° clockwise from x. The polarities of these axes determine the polarity of ground motion in any component direction (e.g., downward ground motion recording as positive values on the vertical‐geophone trace). According also to this SEG standard, a pressure decrease is to be recorded as positive output on the hydrophone trace. We also recommend a cyclic indexing convention, [W, X, Y, Z] or [0, 1, 2, 3], to denote hydrophone or microphone (pressure), inline (radial) geophone, crossline (transverse) geophone, and vertical geophone, respectively.We distinguish among three kinds of polarity standard: acquisition, preprocessing, and final‐display standards. The acquisition standard (summarized in the preceding paragraph) relates instrument output solely to sense of ground motion (geophones) and of pressure change (hydrophones). Polarity considerations beyond this [involving, e.g., source type, wave type (P or S), direction of arrival, anisotropy, tap‐test adjustments, etc.] fall under preprocessing polarity standards. We largely defer any consideration of a display standard.

Reflection moveout inversion for horizontal transverse isotropy: Accuracy, limitation, and acquisition

Horizontal transverse isotropy (HTI) is the simplest azimuthally anisotropic model used to describe vertical fracturing in an isotropic matrix. Assuming that the subsurface is laterally homogeneous, and using the elliptical variation of P-wave NMO velocity with azimuth measured in at least three different source‐to‐receiver orientations, we can estimate three key parameters of HTI media: the vertical velocity, anisotropy, and the azimuth of the symmetry axis. Such parameter estimation is sensitive to the angular separation between the survey lines in 2-D acquisition or, equivalently, to source‐to‐receiver azimuths in 3-D acquisition and the set of azimuths used in the inversion procedure. The accuracy in estimating the azimuth, in particular, is also sensitive to the strength of anisotropy, while the accuracy in resolving vertical velocity and anisotropy is about the same for any strength of anisotropy. To maximize the accuracy and stability in parameter estimation, it is best to have the azimuths for the source‐to‐receiver directions 60° apart when only three directions are used. This requirement is feasible in land seismic data acquisition where wide azimuthal coverage can be designed. In marine streamer acquisition, however, the azimuthal data coverage is limited. Multiple survey directions are necessary to achieve such wide azimuthal coverage in streamer surveys. To perform the inversion using three azimuth directions, 60° apart, an HTI layer overlain by an azimuthally isotropic overburden should have a time thickness, relative to the total time, of at least the ratio of the error in the NMO (stacking) velocity to the interval anisotropy strength of the HTI layer. Having more than three source‐to‐receiver azimuths (e.g., full azimuthal coverage), however, provides a useful data redundancy that enhances the quality of the estimates, thus allowing acceptable parameter estimation at smaller relative thicknesses.

Reliability analysis in dynamic systems: Implications for positioning marine seismic networks

Real‐time integrated monitoring of reliability (the impact of undetected biases in positioning observations on the position of geophysical elements) during marine seismic surveys is essential to ensure there is no significant loss in the resolution of the processed seismic image. The B-method is currently the most rigorous testing procedure for bias identification. It has been used extensively in geodetic networks, but to date it has found very little application within a dynamic environment. Here the method is expanded for use in dynamic systems—especially in marine seismic positioning networks such as those represented by a multisource, multistreamer, multivessel acquisition system. With this approach, we have found completely rigorous reliability estimates based on an integrated navigation method. We conclude that although the reliability of a system is in general a consequence of the redundancy, its geometry, and the stochastic model of the observations, these factors affect internal and external reliability in rather different ways. A key contribution is the demonstration that simple, easily understandable, and explainable statistics can be used to give a more complete description of quality than that obtained from precision measures alone. Assessing precision alone may give a false sense of security regarding the quality of the location of a seismic spread. The exploration and production industry is now making increasing use of old and new marine streamer 3-D surveys as part of 4-D time lapse reservoir monitoring projects. A more rigorous approach to positioning data quality, such as the method described in this paper, may play a material role in the avoidance of interpretable artifacts in these projects.

Dual‐sensor OBC technology

Before the invention and successful implementation of the towed streamer in the late 1940s, the ocean‐bottom cable (OBC) method, and variations thereof, represented our only means for acquiring seismic data in marine areas. The marine streamer facilitated more rapid acquisition of 2-D data. Its widespread adoption relegated OBC to shallow waters where streamers could not be towed.

On: “The shape of a marine streamer in a cross current” by P. M. Krail and H. Brysk (GEOPHYSICS, 54, 302–308, March 1989).

The work of these authors represents a substantial advance in the technology of marine‐streamer position measurement, by providing a physically realistic fitting and interpolation model. Their work, however, confuses the issue of the equilibrium streamer shape, since they claim that “…currents caused the streamer to drift out of the line of travel of the vessel in a curved shape” (p. 302).

The shape of a marine streamer in a cross current

A serious problem in marine data collection (particularly 3‐D) is the necessity to assign to each hydrophone a precise location on the surface of the earth. The data available for this purpose can come from the vessel’s navigation system, a radio beacon (at the tail buoy), an acoustic transponder (at the head of the streamer and occasionally elsewhere), and magnetic compasses distributed over the length of the cable. The shape of the streamer is commonly reconstructed by fitting a curve’s tangents to the compass readings. The shape deduced in this fashion is highly sensitive to compass errors. As an alternative to the ad hoc numerical fit, we have derived the shape of the streamer in a cross current from physical principles. The mechanical equilibrium of tension and drag forces leads to differential equations which we integrate analytically to obtain a formal solution for the tension. A further analytic integration yields an equation (containing two integration constants) that relates arc length along the cable to the tangent angle. This equation can be matched to compass readings (for stability and minimum error) by a least‐squares estimation of the integration constants. A satisfactory fit is obtained with a representative data set. Parametric equations are also obtained for x and y along the cable (with the x-axis in the fluid flow direction), as functions of the tangent angle; they contain the same integration constants (evaluated by the previous procedure). Elimination of the angle between the two parametric equations yields the equation of the cable shape in Cartesian coordinates.

The shape of a marine streamer in a cross current : Krail, P.M. and H. Brysk, 1989. Geophysics, 54(3):302–308. Texaco, E&P Tech. Div., P.O. Box 770070, Houston, TX 77215-0070, USA

The shape of a marine streamer in a cross current : Krail, P.M. and H. Brysk, 1989. Geophysics, 54(3):302–308. Texaco, E&P Tech. Div., P.O. Box 770070, Houston, TX 77215-0070, USA

Vertical marine streamer

Dispositif de reception d'ondes acoustiques dans l'eau adapte, en position d'equilibre, a se tenir verticalement dans l'eau. Receiving apparatus adapted acoustic waves in the water, in the equilibrium position, to be held vertically in the water. Il comporte un element tubulaire (1) constitue de plusieurs sections (T, a T 6 ) raccordees et comportant des moyens de flottaison du cote d'une premiere extremite, des moyens de lestage (L) du cote de la seconde extremite, plusieurs recepteurs repartis a l'interieur de certaines sections (T, a T,) de l'element tubulaire et des ailerons de stabilisation (5) fixes a la seconde extremite de celui-ci. It comprises a tubular element (1) consists of several sections (T, to T 6) connected and having flotation means the side of a first end, means for ballasting (L) towards the second end, a plurality of receivers distributed within certain sections (T, T,) of the tubular element and stabilizing fins (5) fixed to the second end thereof. Un câble (3) relie l'element tubulaire a un vehicule de remorquage (4). A cable (3) connects the tubular element to a towing vehicle (4). Application a la prospection sismique par refraction par exemple. Application to the seismic refraction eg.

To: Special Report on “SEG Standards for marine seismic hydrophones and streamer cables (February 1987 GEOPHYSICS, p. 242–248)

To: Special Report on “SEG Standards for marine seismic hydrophones and streamer cables (February 1987 Geophysics, p. 242–248). The name of co‐author W. A. Knox was incorrectly given as “A. E. Knox.”