Abstract: The propagation of a compressional wave in a reservoir rock causes the pore fluids to flow within the pores and pore connections; this internal flow of the pore fluid exhibits hysteretic and viscoelastic behavior. This nonlinear behavior is directly related to the viscosity of the pore fluids. Pore fluids that have higher viscosity like oil, after being disturbed due to a sudden change in pressure applied by a seismic impulse, require a larger time-constant to return to its original state of equilibrium. This larger time-constant generates lower seismic frequencies, and becomes the differentiating characteristic on a seismic image between the lower-viscosity pore fluid like water against the higher-viscosity pore fluid like oil. Mapping these lower frequencies on a seismic reflection image highlights the oil-bearing volume of the reservoir rock formations versus the volume of the reservoir rock formations saturated with water or gas.

Abstract: A method for determining the location and the orientation of the open natural fractures in an earth formation from the interaction of the two seismic signals, one signal transmitted into the formation from one wellbore and the second signal transmitted from the surface of the earth, the interaction of the two seismic signals as they simultaneously propagate through the fractured space is recorded in the second wellbore. The seismic signal transmitted from the surface is a lower frequency acoustic pulse of large amplitude identified as ‘modulation’ wave and the signal transmitted from the wellbore is a higher discrete frequency seismic signal, identified as ‘carrier’ wave. The interaction of the ‘carrier’ wave during the compression and rarefaction cycles of the ‘modulation’ signal is recorded.