Reducing exploration and development risk by diffraction imaging

While production from old and conventional fields on the decline, oil, and gas companies are looking intoincreasingly challenging areas-deep water, subsalt, and in unconventional carbonate reservoirs. Seismicimages in these environments are often of reduced quality, and new innovative seismic technologies are neededto reduce risk in these settings. Fault and fracture identification is, probably the biggest challenge for the seismicin carbonate and unconventional reservoirs. A major challenge in carbonate environments is to mapheterogeneities which have a strong impact on oil and gas production. In many carbonate reservoirs, matrixporosity contains the oil in place but the permeability is mainly provided by fracture corridors. In otherreservoirs, the oil in place is found primarily in karstic caves. Even using the most advanced imaging andinversion techniques, it is extremely difficult to identify small faults and characterize the distribution offractures. Well information can successfully locate faults and provide directional trends of fractures only nearthe wells. Unfortunately, the reliability of detection small and medium scale (less than the seismic wavelength)heterogeneities and possibility characterize their properties in conventional processing and imaging is generallylow. Conventional imaging methods which are biased towards smooth continuous reflectors are intrinsicallylimited when confronting challenges in detection and delineation of these subsurface elements. Seismicmigration treats reflection and diffraction differently (Khaidukov et al., 2004). While diffracted waves arefocused to a diffraction point at depth, the wavefront of the extrapolated reflected wave is not focused but istangent to the reflector. Focusing of the reflection would occur at the imaginary source point. In the migratedsection, we see reflectors as an envelope of the secondary fictitious diffraction. As a consequence, interpretationof seismic images is of limited use for the characterization of subsurface singularities and discontinuities. Inregular migration and inversion, scattered wavefronts from small scattering objects are usually masked by thestronger reflection energy and noise. Small-scale subsurface elements usually are not included in the estimatedvelocity model, and they may, therefore, be considered as defects or damaged regions of the velocity model.Information about structural discontinuities and small-scale subsurface elements is coded in diffracted waves,and they can be detected by diffraction imaging (Landa, 2012). Diffraction imaging aims to focus the diffractionenergy into its origins, namely, into subsurface discontinuities and local heterogeneities which created theregistered diffraction wavefield. The separation between reflective and diffractive components of the totalwavefield is at the core of the diffraction imaging.