Background

Time-lapse (4D) seismic methods attempt to quantify the difference in the seismic response of the subsurface before and after human interference, mainly hydrocarbon production and fluid injection. Multiple theories and case studies have been published. To mention just a few of them, we refer the reader to Calvert (2005), Osdal et al. (2006), Gommesen et al. (2007), Ebaid et al. (2008), Dvorkin (2008b), Ghaderi and Landrø (2009), Trani et al. (2011), and Ghosh and Sen (2012). The main idea is to interpret the temporal changes observed in the seismic response of the subsurface in terms of hydrocarbon saturation, pore pressure, and temperature in order to ascertain bypassed pockets of hydrocarbons and, eventually, increase the recovery factor.

Perhaps the first glimpse into the physics of time-lapse monitoring was in Nur (1969) where the ultrasonic-wave compressional velocity was measured on a granite sample with just 1.5% porosity as the water was draining from the originally fully saturated sample (Figure 10.1). Later, Wang (1988) discovered that the velocity in rock samples saturated with heavy oil strongly decreases when the samples are heated.