PROJECT DESCRIPTION

Note:
The following is a revised submission of a proposal submitted for support of a Workshop on 3D seismic reflection imaging. This submission amplifies and extends number of themes described in the original proposal. In particular it adds a third day to the meeting that focuses on practical issues of survey design that directly relates to the capacity of the R/V Marcus G. Langseth.

Introduction

The capability of the U.S. academic marine geoscience fleet will be significantly improved with the addition of the research vessel R/V Marcus G. Langseth in early 2006. The Lansgeth, which until recently was collecting commercial quality 3D seismic data for Western Geco (as the Western Legend) will provide seismic acquisition capabilities well beyond those currently available to US scientists by allowing the systematic collection of high-quality 3D seismic data in a wide variety of environments globally. To date a small number of 3D seismic data acquisition cruises have been run in the US academic community using single streamer vessels acquiring 3D grids by multiple closely spaced lines. 3D data acquisition by this method is very inefficient and limitations such as minimal streamer navigation cause data quality to be less than desirable. The Langseth will make it possible for the academic community to acquire 3D seismic data in a time efficient manner and comparable in quality to industry exploration.

In the commercial sector the introduction of 3D seismic acquisition is credited with being one of the advances in technology that produced the three most significant increments in oil field discovery rate in the last fifty years (the other two are MCS profiling, and directional drilling). Best practices for 3D seismic data acquisition are now well understood and available in extensive literature, and processing software for 3D data is now readily available, very stable and there is a large body of experience in the exploration industry on the processing and analysis of 3D data sets. With the acquisition of the Langseth the academic sector is poised to take advantage of these developments and gain a similar major advance in scientific discoveries. At the same time, because of the very limited experience in our community with the 3D approach many scientists are not fully apprised of the range of new problems that become accessible to study with the 3D approach.

We propose to hold a symposium with the title "3-D Seismic Reflection Imaging: a new opportunity for Marine Geoscience Research." The main purpose is to highlight and examine the many opportunities for research that will become available with the introduction of 3D seismic acquisition capability as a routine methodology in the academic community and the broad impact that studies using the technique will have. We will discuss the academic 3D acquisition programs obtained to date, on the fast-spreading East Pacific Rise (EPR),in subduction zones of the Nankai Trough off Japan and the Barbados system (see Figure 1 below), and from gas hydrate environments (Blake Ridge and Hydrate Ridge) that have already proven their broad value (Tong et al., 2003; Bangs et al., 1999, 2004; Bangs et al., 2000; Gorman et al., 2002). They provide useful case studies for understanding the role 3D seismic images can play in advancing critical areas of basic research. We know now from this work that magma bodies images in the ARAD area of the EPR may be very small (a few hundred meters) and almost equi-dimensional in shape and cannot be resolved with 2D techniques. The scale of complexity of structure on the decollement of the subduction systems off Japan and Barbados and the gas hydrate systems of the Blake Ridge and Hydrate Ridge would never have been apparent from 2D images.

Figure 1. Amplitude of decollement reflection near the toe of the Barbados accretionary prism showing inferred zones of high porosity (bright yellow-orange patches).

We will also engage experts from the oil exploration industry who will showcase some of the studies of complex geological settings that have been illuminated by 3D imaging and analysis. The industry has advanced an extraordinary suite of visualization and image analysis tools that extract unprecedented geological inferences from 3D images in a way that is quite impossible with 2D data. Some of the most useful poststack attributes are instantaneous amplitude, phase, frequency, and Q. These instantaneous attributes, such as shown in the Figure below, have the potential to be powerful indicators of lithologic variations, event continuity, fracturing, and absorption. Prestack seismic attributes such as gradient, intercept, impedance, and P and S reflectivity, are extracted by AVO/AVA (amplitude versus offset or angle) analysis. This procedure has the potential to provide information about lithology, fluid saturation, porosity, and in the case of 3D data even about anisotropy of the targeted subsurface (Castagna, 1993; Yilmaz, 2001).

Figure 2. The interpretive value of instantaneous attributes applied to 3D data volumes (from Liner, 1999). Map view (a) and Time slice (b) on amplitudes are now standard displays. By using this information a detailed porosity map (e) can be derived from sparse logging-based porosity measurements.

Another important area of research that will be covered during the meeting is the current state of knowledge on possible responses of marine mammals to seismic sources, as well as current understanding on the most effective methods of mitigation. We will ask a leader in the field of marine mammal biology, such as Peter Tyack (WHOI), to bring the geophysical community up to date on the latest data regarding marine animal response to seismic sources, how these data are collected, and likely areas of future research. The Langseth when refit for academic work will be one of the best marine mammal observation platforms available to the US research community, and it is expected that the data collected in association with mitigation will be valuable, as well as possible dedicated use of the ship. As the environmental impact of seismic research has become a topic of increasing concern to scientists, environmental groups and the public, it is important that the geophysical community seeking to utilize the seismic capabilities of the Langseth understand the basic issues and scientific data available on the topic.

As a derivative issue, permits for seismic research, particularly in continental margin areas where whales are common have become increasingly difficult to obtain. Quite a bit of experience has been gained in many permitting requests over the last several years and the Workshop will present an opportunity to highlight these issues for potential users.

Leaders of major NSF programs including RIDGE, MARGINS, IODP (all of which have noted the need for 3D imaging in their planning documents) will participate in the symposium to insure their Programs' research objectives receive appropriate consideration. We will also invite scientists who are not themselves reflection seismologists but whose science would benefit by the use of 3D seismic data. Examples might include those interested in fluid flow in sedimentary sections, and biologists interested in the controls on distribution of mid-ocean ridge hydrothermal vents and their associated biota. By including both seismic specialists and non-specialists users of seismic data we will take the broadest perspective on current problems in the geosciences accessible to 3D seismic investigation.

One of the most potent opportunities provided by 3D imaging is the next dimension - 4D. The basic method uses 3D seismic images of the same volume acquired at several different times, perhaps a few years apart, and examines them for changes. To be effective it is essential that the images are all of similarly high quality and that the acquisition parameters closely match also. Hence a vessel of at least the capability of the Langseth is required. The differences between successive images then describe changes in the sub-surface. In oil production the 4D method is routinely used for mapping the draining of producing oil fields and identifying oil that has been by-passed during production. It has proven to be an essential tool to enhance recovery from existing fields. In academic research there are many possible objectives for 4D work, but just building on two of the existing 3D data sets, it is clear that many of the magma bodies imaged by Tong et al (2003) are too small to be thermally stable and would certainly evolve on periods of several years to decades, perhaps governing the location of hydrothermal systems and associated biota. Similarly, the heterogeneous response of the decollement surface in the Barbados prism (Bangs et al., 1999) likely responds to fluid pressure changes that cannot be static and may be implicated in triggering of earthquakes.

An important component of the Workshop will be a practical Clinic on the third day that will address specifics of survey design for particular scientific applications. We will engage the expertise of industry colleagues and the experience of those who have conducted surveys for research objectives to outline survey design strategies that match the scientific objectives to the best field practices. Workshop attendees will be invited to bring plans for 3D seismic survey programs and learn how to match those plans to survey design around the capability of the Langseth. This is designed to be a hands-on session for a sub-set of the total Workshop attendees who have near term plans for seismic studies.

Our hope is to attract a large international participation of perhaps one hundred. We have requested full travel and subsistence for sixty. For planning purposes, we have budgeted round trip airfare and ground transportation at $550 for 50 U.S. participants and $1250 for 10 International participants. We will divide the travel and subsistence costs so that junior scientists, post-docs and students receive a greater proportion of full costs that senior people who would be expected to derive a significant portion of their associated costs. We suggest full support for students, 75% for post-docs and junior scientists and 50% for senior scientists. Lamont-based participants will have minimal support costs and those from Woods Hole Oceanographic will not require air travel so we hope that attendance will be large. If attendance is not as expected and the above distribution leads to residual funds they can be applied towards the additional travel expenses reimbursements.

We will advertise in EOS and Geotimes because it has the greatest readership among anticipated attendees. Additionally, we will use the electronic distribution systems available through RIDGE2K, MARGINS, IODP and IRIS as well as make direct email announcements to key institutions nationally and internationally.

The proposed symposium will emphasize the breadth of the science problems that can be tackled more effectively using 3D imaging (including high-resolution approaches). The meeting will be held at Lamont-Doherty Earth Observatory. John Mutter of Lamont-Doherty and Greg Moore of the University of Hawaii will co-convene the symposium. Two days are scheduled for the meeting, September 8-10, 2005. The Symposium Organizing Committee* will ensure that invited participants provide a balance of scientific and technical disciplines, and institutional representation.

The outcome of the Workshop will be available on the Workshop Web site that will be developed well prior to the meeting date. The site will include a Workshop Proceedings as a record of the meeting and will include all material presented at the meeting including PowerPoint presentations and any background materials.

As a unique outcome we will produce a type of basic "how-to" manual or users guide for use of the Langseth that will give prospective users a basic idea of how to design a proposal for use of the vessel for 3D seismic work. This will derive both from the expertise of the Lamont-based vessel operations group as well as the Clinic session on the third day. It will include case studies of a range of surveys for different objectives in different settings. As a Web document it can be maintained permanently as part of the vessel operations and updated through experience as the community gains experience with use of the vessel in different environments. We have allocated two months of a post-doc (or equivalent) support for this outcome because this particular task requires a person with knowledge of seismic reflection research and time to dedicate to the task.

The Steering Committee will contribute a report to EOS that will point to the Web site for detailed information and the "how-to" manual.

*The Symposium Organizing Committee includes the two Co-Convenors, John Mutter (LDEO) and Greg Moore (University of Hawaii) and eleven others: Greg Mountain (Rutgers), John Diebold (LDEO), Nathan Bangs (University of Texas), Graham Kent (Scripps), Mike Coffin (University of Tokyo), Alastair Brown (consultant), Alberto Malinverno (Schlumberger), Mladen Nedimovic (LDEO), Suzanne Carbotte (LDEO), Maya Tolstoy (LDEO) Jacqueline Floyd (LDEO), and Steve Holbrook (University of Wyoming). All the US academic members of the Symposium Steering Committee met for about 90 minutes at the AGU on December 6th 2004 to plan the Symposium. Mike Purdy also attended.