Recent advances in geophysical technology: introduction and review

Abstract

In many basins and especially those in NW Europe, 3D seismic data have become a necessary prerequisite to development, appraisal and, almost routinely, exploration drilling, but equally they are rarely seen as being sufficient. Why is this, when the majority of industry analysts recognize the value of 3D seismic data to an oil company’s exploration portfolio: are geophysicists too successful at marketing? Are we victims of promising too much, or should we see this hunger for ever more subsurface information as encouragement to refine existing technologies further and to develop new ones?In September 2002, the Geological Society meeting on exploration in volcanic margins heard about a successful strategy of ‘drilling the bumps’, which led to the discovery of the Marjun hydrocarbon accumulation, the first in Faroese waters. Petex 2002 was told that the biggest UK North Sea discovery for a decade had not used ‘geophysical malarkey’. Is seismic technology inadequate, or has it reached its limits as the targets get ever tougher?Evidently, as the remaining basins become covered by seismic surveys, the easy finds are becoming fewer. Having consumed roughly half the world’s proven reserves, new reserves must be found using ever more imaginative geological hypotheses, and remote sensing technologies will need to give access to ever more information and provide discrimination to test the hypotheses and reduce the risk.The quest for resolution is unrelenting and finer spatial sampling is providing significant improvements in imaging. Honouring well information requires more realistic, anisotropic velocity models for pre-stack depth migration which furnish images that are better representations of the drillable geology. The need to qualify the data in a seismic survey has resulted in so many auxiliary measurements of the acquisition system itself that the subsurface data are almost in a minority, but this brings improved, quantified repeatability, with the potential to drive down time-lapse seismic noise and reveal subtle, production-related reservoir changes. Qualified amplitudes and careful control during processing allow inversion for elastic parameters of the subsurface. With good petrophysical and geomechanical models, elastic inversions can benefit both the reservoir engineer and the driller and offer further potential for multi-component acquisition in reservoir characterization. Salt, basalt or complex tectonic overburdens pose their own challenges to imaging and encourage potential field measurements to complement seismic data in velocity model building and the prediction of reservoir rocks or fluids. Very long offsets and very low seismic frequencies may also have a rô le to play in these environments. Breakthroughs in data handling and visualization technology allow us to take full benefit of these improvements.The stimulus for innovation is as strong as ever and, even if the immediate economic context is uncertain, the industry is responding. This paper will review several of the current technology trends and offer some speculation on the road ahead.