Marine Geophysical Site Investigation for Exploration Drilling Rigs: Survey Contracts Appraisal

Abstract

The very substantial change in the scope of equipment and services offered by the marine geophysical site investigation contractor during the last fifteen years, and the investment costs which this change inevitably must incur, is not in line with the nature of site-specific survey contract awards as practised by the majority of oil companies in the North Sea and many international areas. Comparisons are discussed between site-specific survey contracting in these areas and the situation which prevails in the USA, where there is a requirement to survey the whole of a leased block and present the results to a government-appointed controlling body for approval and comment. In the USA subsequent site-specific analysis can either make use of data acquired in the block survey or, if there is cause for concern, additional investigation of a very restricted area can be commissioned. The deficiencies of site-specific surveys in isolation are discussed in detail and a case is made for the more general adoption of a two-tiered programme of investigation with ‘regional’ coverage supported, where necessary, by separately commissioned site-specific surveys or drilling investigations designed to further define or substantiate the ‘regional’ observations.

This should subtantially improve the efficency, value and reliability of marine geophysical site investigations. It will also allow the site survey industry to eventually structure itself into a mix of a relatively small number of large, well-equipped and very efficient data acquisition vessels supported by smaller vessels and specialist project units.

With this sort of structure and the alleviation of the problems accompanying fast turnaround site-specific acquisition and reporting, there is scope for consideration of industry-accepted ‘codes of practice’ in line with the regulations which control site investigation procedures in civil engineering studies.

The years 1970-1985 have seen a major expansion in the number of contractors undertaking marine geophysical site investigation surveys, and in the range and complexity of instrumentation and hardware available. The period has also seen a substantial growth in continental shelf exploration, including movement into deeper water and away from the established areas of the USA, the North Sea, the Arabian Gulf, and South-East Asia. The commercial pressures on the contractor to exploit the market and keep pace with the technology have proved challenging, but the financial return on investment is highly unpredictable, though traditionally low. The number of survey companies which have been closed down, endured long periods of severe financial restriction or been subject to takeover and major restructuring, is perhaps too high to be regarded as healthy. If the survey contractor cannot expect an adequate financial return on his investment, then the interests of the equipment supplier/manufacturer and the oil exploration company/drilling contractor and civil engineering contractor must inevitably also suffer when out-of-date equipment becomes the norm and professional practices in acquisition and interpretation are limited by the contractor’s own commercial considerations.

This paper describes many of the commercial and technical factors which are considered by the contractor when preparing bids for surveys. The paper also updates and extends some of the points of discussion which closed the geophysical survey section of the 1979 Site Investigation Conference. Some comparisons are drawn between survey specifications and contract negotiation in Northern Europe and other parts of the world. The net result is an argument for a more rational and constructive approach by both the geophysical contractor and by the oil and engineering companies and governmental institutions which direct the scope of work issued.

The paper is structured around the industry of providing geophysical site investigation studies for marine exploration drilling rigs. No accounting is made of similar sur vey works which can accompany oil production construction and development.

It will be helpful first to state the two aims of the geophysical site investigation survey for exploration rigs:

• (1) To define and delineate those features which are a hazard to the safety and integrity of any drilling exploration structure or vessel within a specified area of operation.

• (2) To assemble and suitably present as much geological, geotechnical, hydrographic and environmental information as is practical within a certain budget, and agreed scope; and to aid the timely, efficient, safe siting of the rig and its subsequent spudding and early drilling phases.