Processing/integration of simultaneously acquired 3D surface seismic and 3D VSP data

Abstract

VSP surveys use surface sources and borehole receivers and record both downgoing and upgoing wavefields. Different configurations of VSP surveys are possible and the various types of VSP data sets are valuable to the interpreter in areas where surface seismic data are of limited help. Common applications of zero-offset VSPs are correlating logs and seismic data, getting information about variations in seismic velocity with depth, and detecting multiples. Offset VSPs are usually recorded where subsurface structures are not well known, or are complex. Their images, which are of higher frequency than surface seismic, are used to obtain structural detail around boreholes. Multioffset or walkaway VSPs are a means of lateral reservoir definition away from the borehole. They combine the advantages of VSP (including the possibility of anisotropy determination) with the continuous profiling aspects of surface methods. However, these single or multioffset VSPs are usually obtained as 2D sections and these sections, though useful, cannot be used to construct a 3D data volume around the borehole. Different acquisition geometries are needed to achieve that objective. The first 3D VSP acquisition was attempted in 1986 by AGIP, and several have been acquired since then (Table 1). Simultaneous acquisition of 3D VSP and 3D surface seismic acquisition has been attempted on several occasions and the results have been encouraging in terms of cost effectiveness and the enhanced imaging of the subsurface. This innovative acquisition and analysis offers exciting possibilities for determining data attributes such as anisotropy, Q, and measurement of reflection and transmission amplitudes at the wellbore which can then be used to calibrate AVO attributes estimated from surface seismic 3D data. View this table: Table 1. Some highlights of 3D VSP history Although many 3D VSPs have been discussed in the literature, few articles go into detail about the processing (Gulati et al., 2002). Therefore, a paper …