It is now well recognised that certain types of construction development are, from a geotechnical viewpoint, potentially more hazardous than others. In particular, structures supported at shallow depth below ground level and with a significant ground-related component (such as highway projects, onshore) are particularly exposed to geotechnical risk. Based upon a summary of typical deepwater construction, this paper recognizes that deepwater oil- and gas-related developments may fall in this category. It presents an industry survey to examine current practice and identify deep offshore geotechnical risks and, following a brief review of risk analysis techniques, develops the preliminary stage of a risk analysis for an example deep offshore project. State-of-the-art techniques suitable for deep-water geotechnical investigation are reviewed in the context of hazard investigation and risk minimization
A recent industry-wide survey (Power 2001) has clearly illustrated that, for many aspects of deepwater developments, geotechnical risk is being underestimated or even ignored, with the result that project delays and cost overruns are incurred. One of the conclusions of the survey was that systematic risk evaluations were not being performed Consequently, potential risks were being overlooked, or, if acknowledged, were not being adequately communicated down the supply chain or addressed at the right level or at the right time.
The use of systematic geotechnical risk assessment techniques has gained widespread acceptance in the U K onshore construction industry over the last 5 years (Clayton, 2001a, 2001b), but has yet to take hold offshore.
It is the intention of this paper to illustrate the potential benefits of such an approach and to open the debate regarding the value of this methodology. To do this, it first reviews the typical structures and infrastructure used to develop a deepwater hydrocarbon accumulation and the potential impact of seabed soil conditions on their design, installation and operation.
It then describes the risk analysis, modelling and management techniques that are in common geotechnical usage and could be applied in an offshore context. The industry survey, that prompted this paper, is described and its findings summarised. An actual deepwater field development, currently under evaluation, is used to illustrate one approach to more systematic and cost-effective geotechnical risk assessment. Since an essential part of risk evaluation is the collection of the necessary site data, the current state-of-the-art in deepwater geotechnical data acquisition is also briefly summarised.
Finally some conclusions are drawn, and recommendations made on how a more rigorous approach to geotechnical risk assessment can help reduce:
Cost and time overruns
Health and Safety concerns
Adverse environmental impact
Typical deepwater structures and their geotechnical challenges
The majority of deepwater hydrocarbon developments are exploited by means of either subsea structures, or by a combination of subsea structures and floating production systems. A typical field layout is illustrated in the schematic Figure 1.