Spatial Interpretation of Marine 3D Seismic Project Specifications: An Effective Way toReduce Costs
Authors: Monk D. , Hume J. 
Published: October 2008

One of the driving forces in technology development for 3D surveys has been the need to reduce acquisition and processing costs. Millions of dollars have been poured into developing more and more sophisticated technologies, larger numbers of cables in the water or channels on the ground andmore sophisticated source deployment methods. Many of these methods do indeed save money, but this is not achieved without a price being paid elsewhere.

Our aim in this paper is to suggest that rewriting 3D project specifications and contracts and developing a new method of interpreting quality attribute information, can alsoachieve major cost savings. Quality Attribute Information (QAI) coupled with proper planning of a 3D survey and an understanding of the likely results of acquisition compromises, are two of the most effective steps that can be taken to reduce survey costs while increasing data qualityand data interpretability.

The majority of 3D marine project specifications have their roots in the mid 80's where nearly all acquisition was of a linear nature. 3D surveys were collections of closely spaced2D lines. Much of the technology at the time was designed to take advantage of this situation. In marine acquisition, nearly all specifications were written to consider the data in shot sequence and heavy emphasis was placed on end of line quality statistics for QC purposes. In the 90's, acquisition geometries in land, marine and transition zone surveys are far more complex and linear assumptions need to be reexamined as they not only cloud the "geophysically significant" issues but often add to survey cost by causing crew shut downs in conditions where, when considered in a3D context, operations should continue.

3D survey specifications should be "objective oriented" (See for example Monk and Ridyard 1994), and should bebased on eliminating "geophysically significant" errors by interpreting quality attribute data in a spatial rather than a linear sense. In this paper we present some suggestions about the types of changes that need to be made in tenders, specifications and contracts to accommodate this approachand we provide examples showing the superior nature of this type of evaluation in different kinds of 3D survey projects.

In our model it is essential, for example, for the survey planner to understand the limitations of processing technology in a certain geographical area and to understand the interpreter's objectives. It is imperative that the tenderevaluators understand the possibility of the development of non-geological amplitude anomalies from certain acquisition geometries. It is essential for the interpreter to understand the built in compromises that have been incorporated in the survey design which can effect the [mal data quality and interpretability.

Discussion

The seismic industry has seen a progressive reduction in the cost for marine 3D seismic surveys over the last 10 years. While specific project costs are always dependent on the location and size of the survey, the availability of vessels, and prevailing weather conditions, it is possible to form an averaged cost I sq. km of seismic data acquired if informationis assessed over many surveys.