Abstract
Fractured reservoirs have been encountered worldwide and in general they are profitably produced, however it is safe to say that none of them have been depleted efficiently. As the petroleum industry focuses less on exploration and in a market of rising costs it is becoming more important to recognize the presence of fractures early in the life of a field for optimal reservoir management. Fractures can significantly complicate the behavior of reservoir porosity and permeability, often resulting in numerous dry wells and higher production costs. A key strategy for fractured reservoir management is a quantitative description of the geology, geophysics and petrophysical attributes obtained from seismic methods during production and development.
3D multicomponent seismic surveys, where compressional waves excite shear-wave reflections (PS-waves), can provide complimentary surface-seismic information to help identify fracture properties early in the production history of a reservoir. Based on measurements of shear-wave azimuthal anisotropy, PS-waves can identify fracture density and strike, and because of their asymmetry they are also sensitive to fracture dip. Examples from both land and marine 3D PS-wave surveys demonstrate the potential of using these attributes to characterize subsurface stress variations that are important for open fracture development. The intermediate-scale seismic anisotropy properties obtained from PS-waves will be critical for solving specific production problems associated with different fractured reservoir types, and could improve reservoir modeling: production-history and pressure-test matching, and fluid-flow simulation. From an economic point of view, if PS-wave surveys acquired over the life of a field can prevent a small fraction of unproductive wells, they are worth the expense.
