Geohazard 3D Lessons from European Experience

Abstract

Abstract The paper discusses the use of 3D exploration seismic data for geohazard evaluation purposes. as based on a body of data from i] number of recent cases on the European continental shelf, Comparison is made with conventional high-resolution 2D site survey data, An assessment of the current impact of the technique on the market in Europe, which takes account of theviews of several operators. Introduction Over the past few years [here has been increasing interest in the use of exploration 3D seismic to improve the detection of shallow gas and other drilling hazards. The Fugro/Geoteam companies in Europe, especially Geoteam AS in Oslo, have been contracted on a range of projects to interpret existing exploration 3D seismic data for assessment. This has been undertaken using data from several North Sea area for various clients. the majority to date on the Norwegian continental shelf. Often the 3D data has been used in conjunction with acquisition and integration of conventional 2D high resolution (FIR) seismic site survey data, or other complementary seismicdata. but in some cases the shallow gas geohazard as assessment has been made, at the client's request. using only 3D seismic data. To optimise the exploration 3D seismic data, reprocessing work is currently underway on one central North Sea site to attempt to improve resolution To obtain a snapshot of the wider picture of the use of geohazard 3D in Europe, some views of operators have been sought. and the market impact this represents is discussed. A related activity has been the performance of a small number of trials conducted in full high-resolution 3D seismic acquisition for geohazard objectives. This approach is currently not standard geohazard survey practice and still in the development stage. it merits separate discussion and is outside the scope of this paper. Geoteam Experience Approach. A 3D seismic geohazard evaluation is typically commissioned before a site survey, to enable better planning and optimisation of the later data acquisition. It can, however, be performed alongside the interpretation of the 2D site survey data. to produce an integrated report. 3D evaluation is also leading, particularly in Norway, to a reduction in the amount of l-fR2D acquired. A complementary HR2D survey can then, if the site is suitable, be as limited as a crossed pair of lines at the location. 3D evaluation has also been used alone, if the area is sufficiently familiar, has suitable geology and has been densely sampled by previous drilling. Methodology. With reference to the usual types of supporting geological information (previous wells, regional geological information etc.) the 3D data is interpreted by picking significant horizons. from sectional and time slice views, and producing isochrons (i.e. structure maps) and reflection strength maps of these horizons. Modern workstations are utilised for the interpretation: Charisma in Norway, and Western OASIIS in the U.K.