Abstract: A monofrequency signal is used to record signature properties of subsurface reservoir formations. While recording conventional Vibroseis data after certain prescribed distances, the monofrequency signal is transmitted to evaluate the presence of reservoir rocks underneath that source location. When a compressional wave travels through a permeable and fluid-saturated reservoir formation, the Drag Wave travels through reservoir fluid interconnections at a slower velocity than the compressional wave in the rock matrix. Due to the Doppler Effect, a unique lower frequency is generated. This lower frequency becomes an indicator of the presence of reservoir formations. Its character depends on the tortuosity of pore interconnections, presence of pore fluids, and permeability. A transfer function is calculated to convert the swept frequency signal used for conventional seismic recording. This converted swept frequency signal is cross-correlated with the normally recorded signal.

Abstract: A monofrequency signal is used to record signature properties of subsurface reservoir formations. While recording conventional Vibroseis data after certain prescribed distances, the monofrequency signal is transmitted to evaluate the presence of reservoir rocks underneath that source location. When a compressional wave travels through a permeable and fluid-saturated reservoir formation, the Drag Wave travels through reservoir fluid interconnections at a slower velocity than the compressional wave in the rock matrix. Due to the Doppler Effect, a unique lower frequency is generated. This lower frequency becomes an indicator of the presence of reservoir formations. Its character depends on the tortuosity of pore interconnections, presence of pore fluids, and permeability. A transfer function is calculated to convert the swept frequency signal used for conventional seismic recording. This converted swept frequency signal is cross-correlated with the normally recorded signal.

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.