Patent attributes
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. Only the presence of the reservoir formation is highlighted; non-reservoir formations are not displayed.
