ABSTRACT Recent advances in seismic technology, while spectacular in accomplishment, have been tied only rather loosely to the underlying geology. As one example, 3D surveys have primarily progressed imaging of structures, but have had more limited success with stratigraphic objectives, particularly for Consolidated formations. Such applications are, however, starting to emerge as, for example, use of the Amoco Coherence methods in delineating channels on time slice presentations. At the same time, improvements in geologic understanding and newer tools such as basin models remain poorly coupled to seismic technology. Seismic stratigraphy remains at present a qualitative method—almost an art. Underlying all seismic methods, AVO, Tomography, Trace Inversions, VSP, etc ., are fundamental ideas which are quite simple. The basic geological mechanisms by which sedimentary rocks are formed and rearranged are also in themselves readily understood. In bringing together sea level changes, sediment flows and tectonic processes with Fresnel Zones, and Wave theory we attain remarkable insights into the information potential of seismic data and a new view of the role of such data. Interactive systems, 3D data, basin models, stratigraphic concepts, and other key technological directions, when effectively coordinated and integrated with one another, can offer the most definitive descriptions of the subsurface yet attainable for finding and defining hydrocarbon reservoirs. We consider here the early steps toward this technology “blending” by example rather than via theory. Such practical view suggests that even more exciting possibilities lie just ahead.

Abstract For over 30 years literature describing relations between well log velocities and densities have been only sporadic, uncoordinated and often excluded one or more key parameters such as lithology or geological age. Model relationships are presumed to hold and tested only qualitatively with little to no effort directed toward refining the models or quantitative reconciliation. In 1986 the concept of the sand/shale acoustic impedance cross-over on Zone II was introduced. Where Zone II exists, it separates strongly contrasting low acoustic impedance sands within shales from the more consolidated but still strongly contrasting high acoustic impedance sands within shales at greater depth. The inconsistent and highly muted reflections characterizing Zone II, and corresponding small fluid signatures make seismic definition especially difficult. Also, familiar tools such as seismogram synthesis and AVO studies give unreliable results in this environment. We also now recognize the relatively widespread occurrence of Zone II. Important potential for hydrocarbons has been established for Zone II—albeit mostly by accident. It remains largely unrecognized and unexplored except for obvious simple structures. Conscious and detailed seismic procedures in conjunction with appropriately organized cataloging of subsurface parameters offer the most effective methods for defining Zone II to date. Applying such techniques constitutes the Challenge, but the rewards could be great indeed.

Abstract In correlating seismic data with subsurface information, It often proves convenient to use normal incidence reflections as the analytic formalism. Recall that the one-dimensional approaches as represented by seismogram synthesis assume a flat-layered subsurface and so the vertical travel paths employed are also taken to be normal incidence. Where two and even three-dimensional simulations are employed, normal incidence rays are important because they approximate the CDP stacked traces guite well and under a wide variety of circumstances. Indeed, the usual field technigues for acguiring seismic data are geared toward satisfying this approximation. Nence it is worthwhile to review the acquisition criteria in order to note how relaxation of certain of them might provide additional information about the subsurface. A Figure and discussion from the familiar text by Dobrin (1) points out that a compressional wave incident on an acoustic impedance contrast (or boundary) generates both compressional and shear reflection and transmission components. Intuitively, the reason that such complex behavior occurs is analogous to the logic which suggests that fractures in rocks must stand vertically rather than horizontally.

Abstract In correlating seismic data with subsurface information, it often proves convenient to use normal incidence reflections as the analytic formalism. This publication covers shear waves, in both land and marine applications, as well as considerations, studies, and modeling techniques dealing with amplitude variation with offset.