Abstract

Three-dimensional seismic exploration data is now being used for a variety of engineering applications. This developing trend is being driven by the widespread availability of 3-D data and the industry's need for fasttracking of deepwater exploration and development projects. On the exploration drilling side, 3-D data are being selectively used for drilling hazards assessments. Important questions being asked by operators when deciding if 3-D data alone are sufficient for hazards assessments include: "What are the risks of not doing a high-resolution site survey?" "How much risk are we willing to accept?" The decision needs to be made on a case-by-ease basis considering the factors listed on Table 1. On the development planning side, 3-D data are being used to provide preliminary assessment of complex deepwater conditions. The philosophy here is to "do the best you can with whatever data are available," realizing that 3-D seismic exploration data alone are not adequate for final site or pipeline route selection or detailed characterization needed for design.

Among the most important benefits of using 3-D data include reducing the time and cost required to complete the exploration/development sequence. Three-dimensional seismic data can delay the need for or reduce the scope of sitesurvey work, and can help avoid field development delays caused by unexpectedly encountering difficult conditions after preliminary design has been completed. Limitations of 3-D data include reduced definition of conditions when compared with good quality high-resolution site-survey data.

Use of 3-D data for engineering applications is expected to increase dramatically in the near future, especially in deepwater areas where seafloor and shallow conditions can be complex. High-resolution 3-D data collection, introduced inthe Gulf of Mexico in 1996 to better define shallow conditions, is also expected to become common where seafloor conditions are complex.

Introduction

As technology improves and the petroleum business becomes more and more competitive, the clear trend is for operators to use 3-D seismic exploration data for engineering applications. Specifically, 3-D seismic exploration data are now routinelybeing used for preliminary site/route investigations and selectively for pre-drilling hazards assessments. Thesegrowing trends are especially noticeable in deepwater, remote, and complex areas.

There are clear benefits and clear limitations in using 3-D data for engineering applications. 3-D data are, in effect, a tool, and like any tool that is used appropriately, clearbenefits and added value can result. And, like any tool, its limitations need to be understood and respected to avoid unfavorable consequences resulting from misuse.

For preliminary site/route investigations the philosophy is: "do the best you can with what you've got". In other words, extract from the 3-D data as much preliminary information about site conditions as you can. Whatever the limitations and deficiencies are, this approach is almost certain to be better than the alternative: to begin conceptual or prelimiruuy design with virtually no information at all. Problems resulting from wrong assumptions about site conditions in complex deepwater areas can cascade through various design and planning efforts, and can multiply as the exploration/ development scenario progresses, often with very costly consequences.

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