The seismic method in the search for oil and gas: Current techniques and future developments

This paper gives a review of current seismic techniques and future developments, with an emphasis on the to-day\´s key issue: seismic inversion (deconvolution and migration). The introduction starts with a summary of acoustical echo-techniques and a description of typical features of the seismic industry. The close relationship, particularly with respect to the underlying theory, in the large variety of applications is emphasized. The widely used statistical model of a single seismic trace (time series related to one source/detector position) is introduced and the one-dimensional inversion techniques "seismic deconvolution" and "parametric trace inversion" are discussed. It is shown that for accurate deconvolution results the seismic time wavelet (source signal plus propagation influences) should be accurately known. It is also argued that if deterministic information of the sub-surface reflectivity is known (geologic information), then parametric trace inversion is the way to go. The one-dimensional discussion is finalized with a number of practical recommendations. The multidimensional model of seismic data is introduced with the aid of wave theory. A distinction is made between "one-way" and "two-way" models. It is shown that unlike two-way models, one-way models neglect multiple scattering along the depth coordinate. The multidimensional inversion techniques "seismic migration" and "inverse scattering" are discussed. It is shown that migration techniques aim for zero-offset reflectivity or acoustic impedance, in inverse scattering techniques separate estimates of velocity and density are computed. The underlying equations are given and the close correspondence is pointed out. The importance of the specification of macro subsurface models (propagation models) in any multidimensional seismic inversion technique is emphasized. Finally, a summary is given on the most important future developments in the seismic industry. For the reader, who is not familiar with the seismic method, it is recommended to start with the Appendix.