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Combined interpretation of PP and PS data provides direct access to elastic rock properties

Compagnie Générale de Géophysique, Massy, France

Corresponding author: RGarotta@compuserve.com

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

Multicomponent seismic has been around for more than 30 years but is still struggling to gain widespread acceptance. Although the benefits of shear-wave exploration are countless, only imaging through gas clouds is regularly implemented—a significant niche perhaps, but a niche nevertheless.

We believe that the main obstacle delaying the routine use of multicomponent exploration is not the cost but the lack of interpretation tools. Our reasoning is that because shear information cannot be easily integrated into the normal interpretation workflow, it is seldom used. This is the factor that renders the extra cost prohibitive.

However, we also contend that, if the right tools allow effortless extraction of the full shear-wave information, the added benefits will far outweigh the acquisition cost. In this paper we present one such tool and show that combined interpretation of PP and PS (converted-wave) data provides reliable estimates of elastic rock properties.

Shear-waves are insensitive to fluids, slower than pressure-waves, and polarized. These three properties suggest that shear-wave exploration has potential for: (1) imaging structure through gas clouds; (2) increased resolution; (3) fluid and lithology discrimination; (4) imaging low-acoustic impedance reservoirs; and (5) fracture detection by analysis of shear-wave splitting.

The difference in velocity between P and S waves is simultaneously responsible for the second benefit and the main impediment to combined PP and PS interpretation. The third benefit (and all others to a lesser extent) requires that PP and PS reflectivity for a given event be compared; however, the difference in arrival time makes this task far from trivial. Other issues, such as attenuation and anisotropy, also must be more effectively treated during processing before any associated benefits can be gleaned from the multicomponent data.

This paper focuses on reconciling the arrival times of the different wave modes and using this information to extract the . . . [Full Text of this Article]