Inferring Stratigraphy from Marine Seismic Data (1975)

ABSTRACT The conventional application of seismic data to mapping the depth and attitude of reflecting interfaces has been supplemented in recent years by measurements of velocity and amplitude, from which one hopes to gain some stratigraphic and lithologic information. Data patterns and angular relationships between events provide clues to lithology and geOlogiQalhi13tory. Such data can be interpreted in terms of elastic/ carbonate/evaporite lithology, competent or plastic rocks, rigid or compactable sediments, depositional processes and environment, direction of sediment source, periods of subsidence/growth/erosion, etc. Special attention is given to (1) resolution of events, (2) the measurement and interpretation of seismic velocity and (3) amplitude measurements. The interpreter must bring imagination and geological and geophysical knowledge together to discover possibilities while avoiding pitfalls of untenable geological conclusions or of misinterpreting seismic data" INTRODUCTION The traditional approach to reflection seismic interpretation has been to, pick reflection events and to map structure without saying anything about the nature of the rocks. It has been struggle enough to find coherent primary reflections, determine arrival times and attitudes, and calculate the locations and dips of the interfaces associated with them. Often the events mapped were discontinuous and we would assume that bedding is parallel and hence infer the arrival time and attitude of a disappeared event by extrapolating parallel to other event fragments the technique of phantoming. This technique often permitted the successful mapping of geological structure. Occasionally we would be able to follow one event and say with reasonable certainty that we were indeed following the same geological horizon. We may not have known the exact identification of the event which we might designate as the "boomer"," Horizon" A," "Miocene marker" "near base Tertiary" or similarly. The first successful reflection seismograph work near Oklahoma City was able to map a distinctive reflection, the contact between the thick low-velocity Sylvan shale and the thick high-velocity Viola limestone. However, the majority of geophysical work ended with the mapping of phantom horizons not specifically identified unless they could be tied to nearby well control. Higher-fidelity seismic systems have resulted fran electronic improvements, information theory, the digital revolution and time; these permit stabilizing reflection wavelets and shortening their duration so that more events can be seen as separate and distinct. Record section displays, especially in variable-area "mode and reduced size, permit us to comprehend more data simultaneously and so see relationships which formerly were not evident. Redundant recording, especially common-depth-point techniques, allow us to remove many of the interferences which formerly obscured primary reflections. Seismic analysis techniques have become more quantitative and we are able to see and measure features (Figure 1) in addition to arrival time and dip, which for many years constituted almost the whole of seismic interpretation.