Processing and modelling of seismic reflection data acquired off the Durham coast

Abstract

Off the Durham coast, the Permian succession above the Coal Measures contains limestones and anhydrite bands with high seismic velocities and reflection coefficients. The consequent reduction in penetration of seismic energy makes it difficult to determine Coal Measures structure by the seismic reflection method. Seismic data sets acquired from this region by the National Coal Board in 1979 and 1982 are used to illustrate that satisfactory results are difficult to achieve. Synthetic seismograms, generated for a simplified geological section of the region, are also used to study various aspects of the overall problem of applying the seismic technique in the area. Standard and non-standard processing sequences are applied to the seismic data to enhance the quality of the stacked sections and the results are discussed. This processing showed that in the 1979 survey, in which a watergun source and a 600m streamer were used, some penetration was achieved but Coal Measures resolution on the final sections is poor. The 1982 data set, shot along a segment of the 1979 line using a sleeve exploder source and a 150m streamer, showed no Coal Measures after processing. Synthetic seismograms, generated using the reflectivity method and a broadband source wavelet, are processed to confirm that a streamer with a length of 360 to 400m towed at a depth of 5-7.5m will be optimal for future data acquisition in the area. It is also shown that the erosion of the surface of the limestone lowers the horizontal resolution of the Coal Measures. Scattering