ABSTRACT
The ability to detect the presence of viable hydrocarbonbearing structures, with sufficient porosity, and with tolerable matrix and mass permeability, are among the challenges of the petroleum geologist, petrophysicist, and geophysicist, whose joint role may last far into the reservoir engineers’ production phase. In this chapter we will give examples of some of the basic ways of ‘seismically illuminating’ reservoirs at larger scale, sometimes extending over 100’s of km2 to depths of 5 km. (Small-scale dipole and monopole sonic logging was described in Chapter 12, because of its intimate connection to rock stress, borehole stability and mud pressure). The larger scale techniques illustrated in this chapter range from cross-well tomography, VSP 2D and 3D multi-azimuth walk-away surveys, 4C multicomponent surveys, AVO and AVOA for detecting fracture orientation, and 4D repeated surveys for tracking reservoir changes over time. One of the causes of such changes is the use of water flooding, which causes various coupled mechanisms, besides an advancing oil/water contact. 4D can also be used for monitoring the effects of compaction, and subsidence. In general, apart from a brief treatment of C-waves or converted P-S waves, we will leave a detailed description of the use of shear wave splitting and polarization for Chapter 15. This remarkable method for characterization of fractured reservoirs is a suitable finale, and a good introduction to the need for more geomechanics (in Chapter 16), for improved understanding of fractured reservoir behaviour.
