With the dwindling number of easy discoveries and ever increasing demand of energy resources, the oil and gas exploration industries are moving to less conventional plays, deeper water, and more difficult terrains. The attendant cost of drilling and extraction has prompted the energy and service companies to invest heavily in seismic data acquisition and processing to harvest as much illumination information as possible about the subsurface. Fortunately, the exploration geophysics community during the past decade has witnessed the parallel emergence of a new exploration geophysics topic – seismic interferometry. Seismic interferometry is a means by which unused events, often discarded as coherent noise, can be recombined to give usable signal for existing imaging algorithms. For example, multiple reflections can be recycled as virtual primaries that can illuminate larger portions of the subsurface than seen by the recorded primaries.
In this lecture I will introduce the concepts underlying seismic interferometry and present the workflows for its implementations and practical applications. I will show various ways to harvest useful signal from portions of the data normally considered as noise in conventional processing. I will use several examples to illustrate the practical benefits of interferometry and other multiple imaging methods: increased subsalt illumination by multiple reflections, tripling of the aperture of usable refraction arrivals by supervirtual interferometry, significant widening of the illumination zone of VSP data by transforming multiples into primaries, and reduction of the cost of imaging by multisource phase encoded migration and waveform inversion.