Recent and future developments in marine acquisition technology (original) (raw)
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Some aspects of survey design for wide‐azimuth towed‐streamer acquisition
SEG Technical Program Expanded Abstracts 2007, 2007
Wide-azimuth towed-streamer acquisition emerged in the last two years as a step change in marine acquisition technology in the Gulf of Mexico. This came about because the risky exploration and development of deepwater subsalt reservoirs required seismic data to have better illumination, higher signalto-noise ratio, and improved resolution. Early results from the initial programs confirm that the expected benefits can be obtained. However, although the survey design principles for land and OBC wideazimuth programs are well understood, the fact that the towed-streamer implementation is still in its infancy means that survey design principles in that case are still evolving. The objective of this paper is to discuss some of those principles.
SEG Technical Program Expanded Abstracts 2006, 2006
marine-streamer data is affected by free-surface reflections. They strongly modulate the spectrum reducing energy at the so-called notch frequencies, f n = iv/2z {i = 0,1,…,Ǟ}, in which v is the water velocity and z is the source or receiver depth. As a result there is a very strong loss of useful low-frequency energy and usually a similar loss at higher frequencies. The ghost effect occurs both at the source and at the receiver. At the source, the upgoing part of the source wavefield is reflected off the free surface with inverted polarity before its delayed journey into the Earth. At the receiver, the upgoing part of the receiver wavefield is reflected off the free surface with inverted polarity before it travels down to the receiver again. The over/under acquisition method allows separation of the up-and downgoing wavefields at the source (or receiver) using a vertical pair of sources (or receivers) to determine wave direction. In this article, we present the results of two experiments conducted in the Gulf of Mexico in 2004 and 2006 to investigate the use of over/under sources and receivers.
12th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 15–18 August 2011, 2011
I n geologically complex areas, the limited azimuth range associated with single-vessel straight-line acquisition can result in the target reservoir being poorly and/or randomly illuminated by the deployed surface spread. While the source wavefront propagates in all directions, only a small proportion of the reflected wavefront is captured by the surface receiver spread. Driven primarily by the need to improve subsalt illumination in the Gulf of Mexico, the industry experimented with a number of multivessel geometries; most recently, coil shooting has been deployed over a number of complex geologies worldwide. The first coil shooting survey offshore Brazil was recently acquired with the goal of improving the imaging of the pre-salt target reservoirs for an exploration project. Coil shooting is a technique in which a single towed-streamer vessel shoots a circular “line”. This circular line is repeated inline and crossline to build up fold, offset, and azimuth distribution. This paper will present the survey design process and results, and additionally, present some of the challenges involved in planning and acquiring this unique geometry.
Second International Meeting for Applied Geoscience & Energy
New and innovative survey design solutions for marine towed streamer acquisition were recently introduced by Widmaier et al. (2019). One of the key technical elements was the concept of wide-tow multi-sources, i.e., the distribution of multiple sources along the front of a streamer spread. All the wide-tow source case studies acquired in recent years have made use of uniform multi-source and multi-streamer spreads (i.e., regular streamer and source separations), thus following the same industry standards as in marine seismic surveys with the typical narrow source configurations. However, uniform configurations may not always be feasible or optimal due to operational or geophysical constraints. In this article, we revisit the basics of the wide-tow multi-source method and make the step from a uniform to a non-uniform design. The first seismic survey using this novel method has recently been acquired in a challenging area offshore Malaysia.
Broadband Seismic Methods for Towed-streamer Acquisition
74th EAGE Conference and Exhibition incorporating EUROPEC 2012, 2012
One of the limiting factors in seismic resolution for marine towed-streamer acquisition is the ghost effect due to sources and receivers. The ghost is the reflection from the sea surface that interferes constructively or destructively with the primary reflections reducing the seismic bandwidth at the low end and the high end of the spectrum. Different acquisition and processing solutions were proposed during the years to address the ghost problem. In this paper we review these solutions and we introduce new slant streamertype acquisition with the processing based on prestack single-streamer deghosting.
Broadband Marine Towed Streamer Acquisition; South China Sea Case Study
ASEG Extended Abstracts, 2010
Summary The following paper details the analysis of a 2D broadband marine seismic project acquired offshore China. The deployment configuration included overunder sources and three streamers towed at different depths(5, 17 and 23m). This specific configuration allows for analysis of dual tow depth as a method for increasing bandwidth but also allows for evaluation of two distinct dual tow depth combination solutions over/under and sparse/under. This paper will review the theory behind the two combination techniques, compare the seismic datasets, and finalize with some conclusions on the relative benefits both in terms of seismic imaging and acquisition efficiency.
Steering on grid: An efficient way to reduce infill rate for towed-streamers surveys
First International Meeting for Applied Geoscience & Energy Expanded Abstracts
The cost and turnaround of a towed streamers 3D survey can be significantly impacted by the amount of acquired infills. Local variations of oceanic currents that modify the streamers drift create CMP coverage gaps. These gaps must be mainly filled in by costly infill lines otherwise the subsurface is not properly sampled. The steering strategy, i.e. the way seismic vessel navigators adapt the course of the vessel, is the predominant parameter to avoid gaps between adjacent lines and consequently optimize the infill rate. Steering devices and fan mode shooting can also contribute to this optimization but at a minor degree. On a number of surveys, Total has instigated an innovative strategy based on steering an offset group on the pre-defined CMP grid. This paper introduces the 'steering on grid' method and illustrates its pros and cons when compared to the standard steering for coverage methodology. This assessment was done during a single 3D survey, allowing evaluations within the same environmental frame.
Developments in Marine Seismic Acquisition: Wide-Tow and Beyond
International Petroleum Technology Conference, 2016
The future demands of exploration demand new techniques which increase the efficiency or quality, or even both of marine seismic data. This can be achieved by using the latest geophysical acquisition techniques and geometries in conjunction with developments in processing. By using recently developed deflectors large wide-tow streamer spreads have become possible which allow for regional 3D surveys to replace 2D surveys, at a relatively low cost increase, but reducing the asset development time by basing initial target evaluation on 3D, albeit low quality, rather than 2D. To gain conventional quality 3D survey the lines can be interleaved to halve the cross-line bin size at a later date where needed based on the initial interpretation. We can also look to incorporating wide spreads with more than two sources –this maintains the spatial sampling and hence quality-but requires shorter shotpoint intervals so that inline fold is maintained. This implies that shots will overlap and that ...