The Use of Exploration 3D Data in Geohazard Assessment: Where does the Future Lie?

Abstract

Abstract Increasing use is being made of exploration 3D datssets in geohazards evaluations. This new attitude towards the use of exploration data has occurred whilst operators have been revising all their oilfield working practices. The streamlined approaches to exploration through to development have required site investigation practices to be refined to allow business plans to maintain the speed and momentum of their projects whilst ensuring safety. Using explorers's 3D data to screen potential well or platform locations or even pipeline routes the Site Investigation Specialist can ensure that inappropriate locations or routes are not surveyed whilst minimizing survey costs. Introduction 3D seismic data is not a new phenomenon. The 3D seismic approach has been available to the explorationist for over 20 years. Originally its cost and the length of time it took to process the data meant that the approach was perceived to be of use only to field development and not the exploration phase of prospect evaluation. However, over the last four years there has been a revolution in the turnaround time of 3D data from completion of acquisition to arrival of data for interpretation on the workstation. Whereas turnarounds were previously ofien greater than one year before arrival of first pass processed results, delivery is now regularly within four months of thefinal shot being fired. At the same time the reduction of unit acquisition costs have made the use of 3D data more attractive for use in initial exploration prospect identification. The latter aspect has been largely brought about by the breakthroughs in acquisition approach. Surveys are now being regularly acquired with eight or more streamers allowing ever greater acreage to be covered by 3D surveys faster than ever before and at a lower unit cost. This is well demonstrated in the west of Shetland arena of the UK continental shelf. Irr the beginning of 1990, althoughthe area had seen exploration activity for at least ten years, not one single 3D survey had been acquired. By the end of 1992 only two small 3D surveys over the Clair Field, totalling only 440 square Kilometres, had been acquired. 1993, however, marked a watershed. [n 1993 the number of streamers being towed on 3D surveys began to increase dramatically, this coincided with the 'faster - cheaper 3D' demands of the operators. It also coincided with a surge of renewed interest in the West of Shetland area. The result is that by the end of 1996 some 15500 square kilometres of 3D data will have been acquired in the area However, this explosion in 3D data coverage is not special to this area of the UK continental shelf. The story is repeated across the North Sea and especially in the Gulf of Mexico where either proprietary or speculative 3D datasets provide almost blanket coverage.