R + D Case Histories
This project was commissioned by a major acquisition contractor, in order to understand the relationship between streamer tow width and seismic response. All the factors which could have a bearing on final data quality were analysed as a function of tow geometry using modelled data, calibrated against recorded 3D data where possible. The factors examined included array directivity, AVO, binfill, subsurface illumination, DMO and prestack migration responses. We then developed a unique set of tools to model the seismic response after data processing. Our client was able to build on an impressive cost advantage by demonstrating that the performance envelope of the acquisition system was well understood, and that the geometry design could be optimised for any target.
A fast-track volume from the first 3D survey in an underexplored basin showed an amplitude pattern which echoed the layout of the cross-spread source and receiver lines. Elastic modelling of the stack response showed that this footprint was caused by source-generated noise. The stack response of the noise was changing across the template as a function of the offset distribution in the CMP bins. We developed a process to attenuate this noise pattern after stack, which we called Adaptive Footprint Filtering. The project went on to investigate the effect of geometry design on the footprint, using both elastic modelling and 3D simulations derived from 2D data. This modelling predicted that the footprint would be greatly reduced using a parallel acquisition technique. Approximately 4000 sq Km of data were subsequently acquired over seven fields in the basin using the cost-effective, high quality acquisition designs developed in this project.
The objective of this project was to determine the best strategy for acquiring and processing towed streamer data across several potential license areas. The database for the study consisted of several regional lines acquired with offsets of up to 38Km. The quality of the base basalt and sub-basalt reflections in these data was compared for P-wave and P-SV processing. The same comparison was also made on a series of elastically modelled long-offset records, using basalt thicknesses ranging from a few hundred metres to several kilometres. From these analyses it was possible to predict those areas in which long offset P-SV acquisition would and would not help the interpretation, hence making best use of the seismic budget.
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