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Borehole-integrated anisotropic processing of converted modes

Schlumberger, Gatwick, England, United Kingdom

Corresponding author: leaney@slb.com

The first 20% of the full text of this article appears below.

Processing multicomponent surface seismic data for converted mode imaging is geophysically demanding. The usual challenges confronting conventional P-wave processing are compounded by the problems of determining a second (shear) velocity field, asymmetric raypaths, much stronger anisotropy effects, and often increased attenuation.

In this paper we review our methodology to build and calibrate an anisotropic (VTI), anelastic model at a well and discuss how this model is used to process multicomponent data. One benefit of our calibrated model-based approach is that the viability of using other propagation modes such as PSs events can be easily assessed. Another benefit is that processing can happen directly in depth, although a more conventional time-based processing sequence is also enhanced with a simplified workflow that is consistent for moveout correction and CCP binning.

	Arguing for borehole data integration

 
Standard time processing of converted waves requires determining two effective velocity fields to moveout correct and stack the Pp and Ps data, assuming an initial value for vertical V_P/V_S. Once this is done, the processor often correlates geologic events on the two sections or volumes to obtain an improved vertical V_P/V_S ratio in order to properly bin the data into common conversion point (CCP) gathers. CCP binning, in turn, affects the Ps velocity analysis, so some iteration is needed. Alternatively, techniques now exist to scan the data for the necessary V_P/V_S ratios for CCP binning. Either procedure is interpretive and time consuming.

In deepwater OBC cases, the problem of CCP binning is exacerbated by the further asymmetry introduced by the water layer itself. This must be dealt with both for the Ps waves and the Pp waves. Although full 3-D redatuming is desirable, in practice it is not often applied. In such cases the effect of the water layer on binning must be addressed.

. . . [Full Text of this Article]