The impact of converted wave data in unconventional reservoir evaluation

Unconventional resource plays involve the development of some unusual reservoirs, such as shales or other very tight formations with very low natural permeability. Reservoir development for these plays requires the identification of "sweet spots" for fracturing/production purposes, in what is usually a very inhomogeneous "reservoir". The nature of these sweet spots is somewhat elusive and we will choose to define the term as any portion of the reservoir that gives enhanced hydrocarbon production after optimization of the reservoir through some mechanical process such as hydraulic fracturing. The geophysical characterization of these sweet spots is highly dependent on the detailed rock properties of the shale, but most often takes the form of some highly optimized seismic attribute obtained after careful seismic processing and a seismic inversion. These seismic attributes may not be derived from p-wave data alone. In fact we will argue that the seismic attributes most often used in the identification of sweet spots in shale plays usually require a reasonably accurate determination of formation density which, in most circumstances, cannot be accurately estimated from p-wave data alone. We will then present the impact of converted waves and the additional information that they can bring to these developments when combined with other data.